Ewout van Bekkum | 5890193 | 2020-11-09 12:46:52 -0800 | [diff] [blame] | 1 | .. _module-pw_sync: |
| 2 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 3 | ======= |
Ewout van Bekkum | 5890193 | 2020-11-09 12:46:52 -0800 | [diff] [blame] | 4 | pw_sync |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 5 | ======= |
| 6 | The ``pw_sync`` module contains utilities for synchronizing between threads |
| 7 | and/or interrupts through signaling primitives and critical section lock |
| 8 | primitives. |
Ewout van Bekkum | 5890193 | 2020-11-09 12:46:52 -0800 | [diff] [blame] | 9 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 10 | .. contents:: |
| 11 | :local: |
| 12 | :depth: 2 |
| 13 | |
| 14 | .. Warning:: |
| 15 | This module is still under construction, the API is not yet stable. |
| 16 | |
| 17 | .. Note:: |
| 18 | The objects in this module do not have an Init() style public API which is |
| 19 | common in many RTOS C APIs. Instead, they rely on being able to invoke the |
| 20 | native initialization APIs for synchronization primitives during C++ |
| 21 | construction. |
| 22 | In order to support global statically constructed synchronization without |
| 23 | constexpr constructors, the user and/or backend **MUST** ensure that any |
| 24 | initialization required in your environment is done prior to the creation |
| 25 | and/or initialization of the native synchronization primitives |
| 26 | (e.g. kernel initialization). |
| 27 | |
| 28 | -------------------------------- |
| 29 | Critical Section Lock Primitives |
| 30 | -------------------------------- |
| 31 | The critical section lock primitives provided by this module comply with |
| 32 | `BasicLockable <https://en.cppreference.com/w/cpp/named_req/BasicLockable>`_, |
| 33 | `Lockable <https://en.cppreference.com/w/cpp/named_req/Lockable>`_, and where |
| 34 | relevant |
| 35 | `TimedLockable <https://en.cppreference.com/w/cpp/named_req/TimedLockable>`_ C++ |
| 36 | named requirements. This means that they are compatible with existing helpers in |
| 37 | the STL's ``<mutex>`` thread support library. For example `std::lock_guard <https://en.cppreference.com/w/cpp/thread/lock_guard>`_ |
| 38 | and `std::unique_lock <https://en.cppreference.com/w/cpp/thread/unique_lock>`_ can be directly used. |
| 39 | |
| 40 | Mutex |
| 41 | ===== |
| 42 | The Mutex is a synchronization primitive that can be used to protect shared data |
| 43 | from being simultaneously accessed by multiple threads. It offers exclusive, |
| 44 | non-recursive ownership semantics where priority inheritance is used to solve |
| 45 | the classic priority-inversion problem. |
| 46 | |
| 47 | The Mutex's API is C++11 STL |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 48 | `std::mutex <https://en.cppreference.com/w/cpp/thread/mutex>`_ like, |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 49 | meaning it is a |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 50 | `BasicLockable <https://en.cppreference.com/w/cpp/named_req/BasicLockable>`_ |
| 51 | and `Lockable <https://en.cppreference.com/w/cpp/named_req/Lockable>`_. |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 52 | |
| 53 | .. list-table:: |
| 54 | |
| 55 | * - *Supported on* |
| 56 | - *Backend module* |
| 57 | * - FreeRTOS |
| 58 | - :ref:`module-pw_sync_freertos` |
| 59 | * - ThreadX |
| 60 | - :ref:`module-pw_sync_threadx` |
| 61 | * - embOS |
| 62 | - :ref:`module-pw_sync_embos` |
| 63 | * - STL |
| 64 | - :ref:`module-pw_sync_stl` |
| 65 | * - Baremetal |
| 66 | - Planned |
| 67 | * - Zephyr |
| 68 | - Planned |
| 69 | * - CMSIS-RTOS API v2 & RTX5 |
| 70 | - Planned |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 71 | |
| 72 | C++ |
| 73 | --- |
| 74 | .. cpp:class:: pw::sync::Mutex |
| 75 | |
| 76 | .. cpp:function:: void lock() |
| 77 | |
| 78 | Locks the mutex, blocking indefinitely. Failures are fatal. |
| 79 | |
| 80 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 81 | locking is undefined behavior. |
| 82 | |
| 83 | .. cpp:function:: bool try_lock() |
| 84 | |
| 85 | Attempts to lock the mutex in a non-blocking manner. |
| 86 | Returns true if the mutex was successfully acquired. |
| 87 | |
| 88 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 89 | locking is undefined behavior. |
| 90 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 91 | .. cpp:function:: void unlock() |
| 92 | |
| 93 | Unlocks the mutex. Failures are fatal. |
| 94 | |
| 95 | **Precondition:** The mutex is held by this thread. |
| 96 | |
| 97 | |
| 98 | .. list-table:: |
| 99 | |
| 100 | * - *Safe to use in context* |
| 101 | - *Thread* |
| 102 | - *Interrupt* |
| 103 | - *NMI* |
| 104 | * - ``Mutex::Mutex`` |
| 105 | - ✔ |
| 106 | - |
| 107 | - |
| 108 | * - ``Mutex::~Mutex`` |
| 109 | - ✔ |
| 110 | - |
| 111 | - |
| 112 | * - ``void Mutex::lock`` |
| 113 | - ✔ |
| 114 | - |
| 115 | - |
| 116 | * - ``bool Mutex::try_lock`` |
| 117 | - ✔ |
| 118 | - |
| 119 | - |
| 120 | * - ``void Mutex::unlock`` |
| 121 | - ✔ |
| 122 | - |
| 123 | - |
| 124 | |
| 125 | Examples in C++ |
| 126 | ^^^^^^^^^^^^^^^ |
| 127 | .. code-block:: cpp |
| 128 | |
| 129 | #include "pw_sync/mutex.h" |
| 130 | |
| 131 | pw::sync::Mutex mutex; |
| 132 | |
| 133 | void ThreadSafeCriticalSection() { |
| 134 | mutex.lock(); |
| 135 | NotThreadSafeCriticalSection(); |
| 136 | mutex.unlock(); |
| 137 | } |
| 138 | |
| 139 | |
| 140 | Alternatively you can use C++'s RAII helpers to ensure you always unlock. |
| 141 | |
| 142 | .. code-block:: cpp |
| 143 | |
| 144 | #include <mutex> |
| 145 | |
| 146 | #include "pw_sync/mutex.h" |
| 147 | |
| 148 | pw::sync::Mutex mutex; |
| 149 | |
| 150 | void ThreadSafeCriticalSection() { |
| 151 | std::lock_guard lock(mutex); |
| 152 | NotThreadSafeCriticalSection(); |
| 153 | } |
| 154 | |
| 155 | |
| 156 | C |
| 157 | - |
| 158 | The Mutex must be created in C++, however it can be passed into C using the |
| 159 | ``pw_sync_Mutex`` opaque struct alias. |
| 160 | |
| 161 | .. cpp:function:: void pw_sync_Mutex_Lock(pw_sync_Mutex* mutex) |
| 162 | |
| 163 | Invokes the ``Mutex::lock`` member function on the given ``mutex``. |
| 164 | |
| 165 | .. cpp:function:: bool pw_sync_Mutex_TryLock(pw_sync_Mutex* mutex) |
| 166 | |
| 167 | Invokes the ``Mutex::try_lock`` member function on the given ``mutex``. |
| 168 | |
| 169 | .. cpp:function:: void pw_sync_Mutex_Unlock(pw_sync_Mutex* mutex) |
| 170 | |
| 171 | Invokes the ``Mutex::unlock`` member function on the given ``mutex``. |
| 172 | |
| 173 | .. list-table:: |
| 174 | |
| 175 | * - *Safe to use in context* |
| 176 | - *Thread* |
| 177 | - *Interrupt* |
| 178 | - *NMI* |
| 179 | * - ``void pw_sync_Mutex_Lock`` |
| 180 | - ✔ |
| 181 | - |
| 182 | - |
| 183 | * - ``bool pw_sync_Mutex_TryLock`` |
| 184 | - ✔ |
| 185 | - |
| 186 | - |
| 187 | * - ``void pw_sync_Mutex_Unlock`` |
| 188 | - ✔ |
| 189 | - |
| 190 | - |
| 191 | |
| 192 | Example in C |
| 193 | ^^^^^^^^^^^^ |
| 194 | .. code-block:: cpp |
| 195 | |
| 196 | #include "pw_sync/mutex.h" |
| 197 | |
| 198 | pw::sync::Mutex mutex; |
| 199 | |
| 200 | extern pw_sync_Mutex mutex; // This can only be created in C++. |
| 201 | |
| 202 | void ThreadSafeCriticalSection(void) { |
| 203 | pw_sync_Mutex_Lock(&mutex); |
| 204 | NotThreadSafeCriticalSection(); |
| 205 | pw_sync_Mutex_Unlock(&mutex); |
| 206 | } |
| 207 | |
| 208 | TimedMutex |
| 209 | ========== |
| 210 | The TimedMutex is an extension of the Mutex which offers timeout and deadline |
| 211 | based semantics. |
| 212 | |
| 213 | The TimedMutex's API is C++11 STL |
| 214 | `std::timed_mutex <https://en.cppreference.com/w/cpp/thread/timed_mutex>`_ like, |
| 215 | meaning it is a |
| 216 | `BasicLockable <https://en.cppreference.com/w/cpp/named_req/BasicLockable>`_, |
| 217 | `Lockable <https://en.cppreference.com/w/cpp/named_req/Lockable>`_, and |
| 218 | `TimedLockable <https://en.cppreference.com/w/cpp/named_req/TimedLockable>`_. |
| 219 | |
| 220 | Note that the ``TimedMutex`` is a derived ``Mutex`` class, meaning that |
| 221 | a ``TimedMutex`` can be used by someone who needs the basic ``Mutex``. This is |
| 222 | in stark contrast to the C++ STL's |
| 223 | `std::timed_mutex <https://en.cppreference.com/w/cpp/thread/timed_mutex>`_. |
| 224 | |
| 225 | |
| 226 | .. list-table:: |
| 227 | |
| 228 | * - *Supported on* |
| 229 | - *Backend module* |
| 230 | * - FreeRTOS |
| 231 | - :ref:`module-pw_sync_freertos` |
| 232 | * - ThreadX |
| 233 | - :ref:`module-pw_sync_threadx` |
| 234 | * - embOS |
| 235 | - :ref:`module-pw_sync_embos` |
| 236 | * - STL |
| 237 | - :ref:`module-pw_sync_stl` |
| 238 | * - Zephyr |
| 239 | - Planned |
| 240 | * - CMSIS-RTOS API v2 & RTX5 |
| 241 | - Planned |
| 242 | |
| 243 | C++ |
| 244 | --- |
| 245 | .. cpp:class:: pw::sync::TimedMutex |
| 246 | |
| 247 | .. cpp:function:: void lock() |
| 248 | |
| 249 | Locks the mutex, blocking indefinitely. Failures are fatal. |
| 250 | |
| 251 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 252 | locking is undefined behavior. |
| 253 | |
| 254 | .. cpp:function:: bool try_lock() |
| 255 | |
| 256 | Attempts to lock the mutex in a non-blocking manner. |
| 257 | Returns true if the mutex was successfully acquired. |
| 258 | |
| 259 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 260 | locking is undefined behavior. |
| 261 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 262 | .. cpp:function:: bool try_lock_for(chrono::SystemClock::duration for_at_least) |
| 263 | |
| 264 | Attempts to lock the mutex where, if needed, blocking for at least the |
| 265 | specified duration. |
| 266 | Returns true if the mutex was successfully acquired. |
| 267 | |
| 268 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 269 | locking is undefined behavior. |
| 270 | |
| 271 | .. cpp:function:: bool try_lock_until(chrono::SystemClock::time_point until_at_least) |
| 272 | |
| 273 | Attempts to lock the mutex where, if needed, blocking until at least the |
| 274 | specified time_point. |
| 275 | Returns true if the mutex was successfully acquired. |
| 276 | |
| 277 | **Precondition:** The lock isn't already held by this thread. Recursive |
| 278 | locking is undefined behavior. |
| 279 | |
| 280 | .. cpp:function:: void unlock() |
| 281 | |
| 282 | Unlocks the mutex. Failures are fatal. |
| 283 | |
| 284 | **Precondition:** The mutex is held by this thread. |
| 285 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 286 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 287 | .. list-table:: |
| 288 | |
| 289 | * - *Safe to use in context* |
| 290 | - *Thread* |
| 291 | - *Interrupt* |
| 292 | - *NMI* |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 293 | * - ``TimedMutex::TimedMutex`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 294 | - ✔ |
| 295 | - |
| 296 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 297 | * - ``TimedMutex::~TimedMutex`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 298 | - ✔ |
| 299 | - |
| 300 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 301 | * - ``void TimedMutex::lock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 302 | - ✔ |
| 303 | - |
| 304 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 305 | * - ``bool TimedMutex::try_lock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 306 | - ✔ |
| 307 | - |
| 308 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 309 | * - ``bool TimedMutex::try_lock_for`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 310 | - ✔ |
| 311 | - |
| 312 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 313 | * - ``bool TimedMutex::try_lock_until`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 314 | - ✔ |
| 315 | - |
| 316 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 317 | * - ``void TimedMutex::unlock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 318 | - ✔ |
| 319 | - |
| 320 | - |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 321 | |
| 322 | Examples in C++ |
| 323 | ^^^^^^^^^^^^^^^ |
| 324 | .. code-block:: cpp |
| 325 | |
| 326 | #include "pw_chrono/system_clock.h" |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 327 | #include "pw_sync/timed_mutex.h" |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 328 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 329 | pw::sync::TimedMutex mutex; |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 330 | |
| 331 | bool ThreadSafeCriticalSectionWithTimeout( |
| 332 | const SystemClock::duration timeout) { |
| 333 | if (!mutex.try_lock_for(timeout)) { |
| 334 | return false; |
| 335 | } |
| 336 | NotThreadSafeCriticalSection(); |
| 337 | mutex.unlock(); |
| 338 | return true; |
| 339 | } |
| 340 | |
| 341 | |
| 342 | Alternatively you can use C++'s RAII helpers to ensure you always unlock. |
| 343 | |
| 344 | .. code-block:: cpp |
| 345 | |
| 346 | #include <mutex> |
| 347 | |
| 348 | #include "pw_chrono/system_clock.h" |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 349 | #include "pw_sync/timed_mutex.h" |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 350 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 351 | pw::sync::TimedMutex mutex; |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 352 | |
| 353 | bool ThreadSafeCriticalSectionWithTimeout( |
| 354 | const SystemClock::duration timeout) { |
| 355 | std::unique_lock lock(mutex, std::defer_lock); |
| 356 | if (!lock.try_lock_for(timeout)) { |
| 357 | return false; |
| 358 | } |
| 359 | NotThreadSafeCriticalSection(); |
| 360 | return true; |
| 361 | } |
| 362 | |
| 363 | |
| 364 | |
| 365 | C |
| 366 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 367 | The TimedMutex must be created in C++, however it can be passed into C using the |
| 368 | ``pw_sync_TimedMutex`` opaque struct alias. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 369 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 370 | .. cpp:function:: void pw_sync_TimedMutex_Lock(pw_sync_TimedMutex* mutex) |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 371 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 372 | Invokes the ``TimedMutex::lock`` member function on the given ``mutex``. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 373 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 374 | .. cpp:function:: bool pw_sync_TimedMutex_TryLock(pw_sync_TimedMutex* mutex) |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 375 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 376 | Invokes the ``TimedMutex::try_lock`` member function on the given ``mutex``. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 377 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 378 | .. cpp:function:: bool pw_sync_TimedMutex_TryLockFor(pw_sync_TimedMutex* mutex, pw_chrono_SystemClock_Duration for_at_least) |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 379 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 380 | Invokes the ``TimedMutex::try_lock_for`` member function on the given ``mutex``. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 381 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 382 | .. cpp:function:: bool pw_sync_TimedMutex_TryLockUntil(pw_sync_TimedMutex* mutex, pw_chrono_SystemClock_TimePoint until_at_least) |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 383 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 384 | Invokes the ``TimedMutex::try_lock_until`` member function on the given ``mutex``. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 385 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 386 | .. cpp:function:: void pw_sync_TimedMutex_Unlock(pw_sync_TimedMutex* mutex) |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 387 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 388 | Invokes the ``TimedMutex::unlock`` member function on the given ``mutex``. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 389 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 390 | .. list-table:: |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 391 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 392 | * - *Safe to use in context* |
| 393 | - *Thread* |
| 394 | - *Interrupt* |
| 395 | - *NMI* |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 396 | * - ``void pw_sync_TimedMutex_Lock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 397 | - ✔ |
| 398 | - |
| 399 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 400 | * - ``bool pw_sync_TimedMutex_TryLock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 401 | - ✔ |
| 402 | - |
| 403 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 404 | * - ``bool pw_sync_TimedMutex_TryLockFor`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 405 | - ✔ |
| 406 | - |
| 407 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 408 | * - ``bool pw_sync_TimedMutex_TryLockUntil`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 409 | - ✔ |
| 410 | - |
| 411 | - |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 412 | * - ``void pw_sync_TimedMutex_Unlock`` |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 413 | - ✔ |
| 414 | - |
| 415 | - |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 416 | |
| 417 | Example in C |
| 418 | ^^^^^^^^^^^^ |
| 419 | .. code-block:: cpp |
| 420 | |
| 421 | #include "pw_chrono/system_clock.h" |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 422 | #include "pw_sync/timed_mutex.h" |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 423 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 424 | pw::sync::TimedMutex mutex; |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 425 | |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 426 | extern pw_sync_TimedMutex mutex; // This can only be created in C++. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 427 | |
| 428 | bool ThreadSafeCriticalSectionWithTimeout( |
| 429 | const pw_chrono_SystemClock_Duration timeout) { |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 430 | if (!pw_sync_TimedMutex_TryLockFor(&mutex, timeout)) { |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 431 | return false; |
| 432 | } |
| 433 | NotThreadSafeCriticalSection(); |
Ewout van Bekkum | 6f5b8fb | 2021-04-06 16:15:22 -0700 | [diff] [blame] | 434 | pw_sync_TimedMutex_Unlock(&mutex); |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 435 | return true; |
| 436 | } |
| 437 | |
| 438 | |
| 439 | InterruptSpinLock |
| 440 | ================= |
| 441 | The InterruptSpinLock is a synchronization primitive that can be used to protect |
| 442 | shared data from being simultaneously accessed by multiple threads and/or |
| 443 | interrupts as a targeted global lock, with the exception of Non-Maskable |
| 444 | Interrupts (NMIs). It offers exclusive, non-recursive ownership semantics where |
| 445 | IRQs up to a backend defined level of "NMIs" will be masked to solve |
| 446 | priority-inversion. |
| 447 | |
| 448 | This InterruptSpinLock relies on built-in local interrupt masking to make it |
| 449 | interrupt safe without requiring the caller to separately mask and unmask |
| 450 | interrupts when using this primitive. |
| 451 | |
| 452 | Unlike global interrupt locks, this also works safely and efficiently on SMP |
| 453 | systems. On systems which are not SMP, spinning is not required but some state |
| 454 | may still be used to detect recursion. |
| 455 | |
| 456 | The InterruptSpinLock is a |
| 457 | `BasicLockable <https://en.cppreference.com/w/cpp/named_req/BasicLockable>`_ |
| 458 | and |
| 459 | `Lockable <https://en.cppreference.com/w/cpp/named_req/Lockable>`_. |
| 460 | |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 461 | .. list-table:: |
| 462 | |
| 463 | * - *Supported on* |
| 464 | - *Backend module* |
| 465 | * - FreeRTOS |
| 466 | - :ref:`module-pw_sync_freertos` |
| 467 | * - ThreadX |
| 468 | - :ref:`module-pw_sync_threadx` |
| 469 | * - embOS |
| 470 | - :ref:`module-pw_sync_embos` |
| 471 | * - STL |
| 472 | - :ref:`module-pw_sync_stl` |
| 473 | * - Baremetal |
| 474 | - Planned, not ready for use |
| 475 | * - Zephyr |
| 476 | - Planned |
| 477 | * - CMSIS-RTOS API v2 & RTX5 |
| 478 | - Planned |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 479 | |
| 480 | C++ |
| 481 | --- |
| 482 | .. cpp:class:: pw::sync::InterruptSpinLock |
| 483 | |
| 484 | .. cpp:function:: void lock() |
| 485 | |
| 486 | Locks the spinlock, blocking indefinitely. Failures are fatal. |
| 487 | |
| 488 | **Precondition:** Recursive locking is undefined behavior. |
| 489 | |
| 490 | .. cpp:function:: bool try_lock() |
| 491 | |
| 492 | Attempts to lock the spinlock in a non-blocking manner. |
| 493 | Returns true if the spinlock was successfully acquired. |
| 494 | |
| 495 | **Precondition:** Recursive locking is undefined behavior. |
| 496 | |
| 497 | .. cpp:function:: void unlock() |
| 498 | |
| 499 | Unlocks the mutex. Failures are fatal. |
| 500 | |
| 501 | **Precondition:** The spinlock is held by the caller. |
| 502 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 503 | .. list-table:: |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 504 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 505 | * - *Safe to use in context* |
| 506 | - *Thread* |
| 507 | - *Interrupt* |
| 508 | - *NMI* |
| 509 | * - ``InterruptSpinLock::InterruptSpinLock`` |
| 510 | - ✔ |
| 511 | - ✔ |
| 512 | - |
| 513 | * - ``InterruptSpinLock::~InterruptSpinLock`` |
| 514 | - ✔ |
| 515 | - ✔ |
| 516 | - |
| 517 | * - ``void InterruptSpinLock::lock`` |
| 518 | - ✔ |
| 519 | - ✔ |
| 520 | - |
| 521 | * - ``bool InterruptSpinLock::try_lock`` |
| 522 | - ✔ |
| 523 | - ✔ |
| 524 | - |
| 525 | * - ``void InterruptSpinLock::unlock`` |
| 526 | - ✔ |
| 527 | - ✔ |
| 528 | - |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 529 | |
| 530 | Examples in C++ |
| 531 | ^^^^^^^^^^^^^^^ |
| 532 | .. code-block:: cpp |
| 533 | |
| 534 | #include "pw_sync/interrupt_spin_lock.h" |
| 535 | |
| 536 | pw::sync::InterruptSpinLock interrupt_spin_lock; |
| 537 | |
| 538 | void InterruptSafeCriticalSection() { |
| 539 | interrupt_spin_lock.lock(); |
| 540 | NotThreadSafeCriticalSection(); |
| 541 | interrupt_spin_lock.unlock(); |
| 542 | } |
| 543 | |
| 544 | |
| 545 | Alternatively you can use C++'s RAII helpers to ensure you always unlock. |
| 546 | |
| 547 | .. code-block:: cpp |
| 548 | |
| 549 | #include <mutex> |
| 550 | |
| 551 | #include "pw_sync/interrupt_spin_lock.h" |
| 552 | |
| 553 | pw::sync::InterruptSpinLock interrupt_spin_lock; |
| 554 | |
| 555 | void InterruptSafeCriticalSection() { |
| 556 | std::lock_guard lock(interrupt_spin_lock); |
| 557 | NotThreadSafeCriticalSection(); |
| 558 | } |
| 559 | |
| 560 | |
| 561 | C |
| 562 | - |
| 563 | The InterruptSpinLock must be created in C++, however it can be passed into C using the |
| 564 | ``pw_sync_InterruptSpinLock`` opaque struct alias. |
| 565 | |
| 566 | .. cpp:function:: void pw_sync_InterruptSpinLock_Lock(pw_sync_InterruptSpinLock* interrupt_spin_lock) |
| 567 | |
| 568 | Invokes the ``InterruptSpinLock::lock`` member function on the given ``interrupt_spin_lock``. |
| 569 | |
| 570 | .. cpp:function:: bool pw_sync_InterruptSpinLock_TryLock(pw_sync_InterruptSpinLock* interrupt_spin_lock) |
| 571 | |
| 572 | Invokes the ``InterruptSpinLock::try_lock`` member function on the given ``interrupt_spin_lock``. |
| 573 | |
| 574 | .. cpp:function:: void pw_sync_InterruptSpinLock_Unlock(pw_sync_InterruptSpinLock* interrupt_spin_lock) |
| 575 | |
| 576 | Invokes the ``InterruptSpinLock::unlock`` member function on the given ``interrupt_spin_lock``. |
| 577 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 578 | .. list-table:: |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 579 | |
Ewout van Bekkum | fe70066 | 2021-04-02 16:48:50 -0700 | [diff] [blame] | 580 | * - *Safe to use in context* |
| 581 | - *Thread* |
| 582 | - *Interrupt* |
| 583 | - *NMI* |
| 584 | * - ``void pw_sync_InterruptSpinLock_Lock`` |
| 585 | - ✔ |
| 586 | - ✔ |
| 587 | - |
| 588 | * - ``bool pw_sync_InterruptSpinLock_TryLock`` |
| 589 | - ✔ |
| 590 | - ✔ |
| 591 | - |
| 592 | * - ``void pw_sync_InterruptSpinLock_Unlock`` |
| 593 | - ✔ |
| 594 | - ✔ |
| 595 | - |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 596 | |
| 597 | Example in C |
| 598 | ^^^^^^^^^^^^ |
| 599 | .. code-block:: cpp |
| 600 | |
| 601 | #include "pw_chrono/system_clock.h" |
| 602 | #include "pw_sync/interrupt_spin_lock.h" |
| 603 | |
| 604 | pw::sync::InterruptSpinLock interrupt_spin_lock; |
| 605 | |
| 606 | extern pw_sync_InterruptSpinLock interrupt_spin_lock; // This can only be created in C++. |
| 607 | |
| 608 | void InterruptSafeCriticalSection(void) { |
| 609 | pw_sync_InterruptSpinLock_Lock(&interrupt_spin_lock); |
| 610 | NotThreadSafeCriticalSection(); |
| 611 | pw_sync_InterruptSpinLock_Unlock(&interrupt_spin_lock); |
| 612 | } |
| 613 | |
Ewout van Bekkum | cc9ef83 | 2021-04-08 08:51:16 -0700 | [diff] [blame] | 614 | Thread Safety Lock Annotations |
| 615 | ============================== |
| 616 | Pigweed's critical section lock primitives support Clang's thread safety |
| 617 | analysis extension for C++. The analysis is completely static at compile-time. |
| 618 | This is only supported when building with Clang. The annotations are no-ops when |
| 619 | using different compilers. |
| 620 | |
| 621 | Pigweed provides the ``pw_sync/lock_annotations.h`` header file with macro |
| 622 | definitions to allow developers to document the locking policies of |
| 623 | multi-threaded code. The annotations can also help program analysis tools to |
| 624 | identify potential thread safety issues. |
| 625 | |
| 626 | More information on Clang's thread safety analysis system can be found |
| 627 | `here <https://clang.llvm.org/docs/ThreadSafetyAnalysis.html>`_. |
| 628 | |
| 629 | Enabling Clang's Analysis |
| 630 | ------------------------- |
| 631 | In order to enable the analysis, Clang requires that the ``-Wthread-safety`` |
| 632 | compilation flag be used. In addition, if any STL components like |
| 633 | ``std::lock_guard`` are used, the STL's built in annotations have to be manually |
| 634 | enabled, typically by setting the ``_LIBCPP_ENABLE_THREAD_SAFETY_ANNOTATIONS`` |
| 635 | macro. |
| 636 | |
| 637 | If using GN, the ``pw_build:clang_thread_safety_warnings`` config is provided |
| 638 | to do this for you, when added to your clang toolchain definition's default |
| 639 | configs. |
| 640 | |
| 641 | Why use lock annotations? |
| 642 | ------------------------- |
| 643 | Lock annotations can help warn you about potential race conditions in your code |
| 644 | when using locks: you have to remember to grab lock(s) before entering a |
| 645 | critical section, yuou have to remember to unlock it when you leave, and you |
| 646 | have to avoid deadlocks. |
| 647 | |
| 648 | Clang's lock annotations let you inform the compiler and anyone reading your |
| 649 | code which variables are guarded by which locks, which locks should or cannot be |
| 650 | held when calling which function, which order locks should be acquired in, etc. |
| 651 | |
| 652 | Using Lock Annotations |
| 653 | ---------------------- |
| 654 | When referring to locks in the arguments of the attributes, you should |
| 655 | use variable names or more complex expressions (e.g. ``my_object->lock_``) |
| 656 | that evaluate to a concrete lock object whenever possible. If the lock |
| 657 | you want to refer to is not in scope, you may use a member pointer |
| 658 | (e.g. ``&MyClass::lock_``) to refer to a lock in some (unknown) object. |
| 659 | |
| 660 | Annotating Lock Usage |
| 661 | ^^^^^^^^^^^^^^^^^^^^^ |
| 662 | .. cpp:function:: PW_GUARDED_BY(x) |
| 663 | |
| 664 | Documents if a shared field or global variable needs to be protected by a |
| 665 | lock. ``PW_GUARDED_BY()`` allows the user to specify a particular lock that |
| 666 | should be held when accessing the annotated variable. |
| 667 | |
| 668 | Although this annotation (and ``PW_PT_GUARDED_BY``, below) cannot be applied |
| 669 | to local variables, a local variable and its associated lock can often be |
| 670 | combined into a small class or struct, thereby allowing the annotation. |
| 671 | |
| 672 | Example: |
| 673 | |
| 674 | .. code-block:: cpp |
| 675 | |
| 676 | class Foo { |
| 677 | Mutex mu_; |
| 678 | int p1_ PW_GUARDED_BY(mu_); |
| 679 | ... |
| 680 | }; |
| 681 | |
| 682 | .. cpp:function:: PW_PT_GUARDED_BY(x) |
| 683 | |
| 684 | Documents if the memory location pointed to by a pointer should be guarded |
| 685 | by a lock when dereferencing the pointer. |
| 686 | |
| 687 | Example: |
| 688 | |
| 689 | .. code-block:: cpp |
| 690 | |
| 691 | class Foo { |
| 692 | Mutex mu_; |
| 693 | int *p1_ PW_PT_GUARDED_BY(mu_); |
| 694 | ... |
| 695 | }; |
| 696 | |
| 697 | Note that a pointer variable to a shared memory location could itself be a |
| 698 | shared variable. |
| 699 | |
| 700 | Example: |
| 701 | |
| 702 | .. code-block:: cpp |
| 703 | |
| 704 | // `q_`, guarded by `mu1_`, points to a shared memory location that is |
| 705 | // guarded by `mu2_`: |
| 706 | int *q_ PW_GUARDED_BY(mu1_) PW_PT_GUARDED_BY(mu2_); |
| 707 | |
| 708 | .. cpp:function:: PW_ACQUIRED_AFTER(...) |
| 709 | .. cpp:function:: PW_ACQUIRED_BEFORE(...) |
| 710 | |
| 711 | Documents the acquisition order between locks that can be held |
| 712 | simultaneously by a thread. For any two locks that need to be annotated |
| 713 | to establish an acquisition order, only one of them needs the annotation. |
| 714 | (i.e. You don't have to annotate both locks with both ``PW_ACQUIRED_AFTER`` |
| 715 | and ``PW_ACQUIRED_BEFORE``.) |
| 716 | |
| 717 | As with ``PW_GUARDED_BY``, this is only applicable to locks that are shared |
| 718 | fields or global variables. |
| 719 | |
| 720 | Example: |
| 721 | |
| 722 | .. code-block:: cpp |
| 723 | |
| 724 | Mutex m1_; |
| 725 | Mutex m2_ PW_ACQUIRED_AFTER(m1_); |
| 726 | |
| 727 | .. cpp:function:: PW_EXCLUSIVE_LOCKS_REQUIRED(...) |
| 728 | .. cpp:function:: PW_SHARED_LOCKS_REQUIRED(...) |
| 729 | |
| 730 | Documents a function that expects a lock to be held prior to entry. |
| 731 | The lock is expected to be held both on entry to, and exit from, the |
| 732 | function. |
| 733 | |
| 734 | An exclusive lock allows read-write access to the guarded data member(s), and |
| 735 | only one thread can acquire a lock exclusively at any one time. A shared lock |
| 736 | allows read-only access, and any number of threads can acquire a shared lock |
| 737 | concurrently. |
| 738 | |
| 739 | Generally, non-const methods should be annotated with |
| 740 | ``PW_EXCLUSIVE_LOCKS_REQUIRED``, while const methods should be annotated with |
| 741 | ``PW_SHARED_LOCKS_REQUIRED``. |
| 742 | |
| 743 | Example: |
| 744 | |
| 745 | .. code-block:: cpp |
| 746 | |
| 747 | Mutex mu1, mu2; |
| 748 | int a PW_GUARDED_BY(mu1); |
| 749 | int b PW_GUARDED_BY(mu2); |
| 750 | |
| 751 | void foo() PW_EXCLUSIVE_LOCKS_REQUIRED(mu1, mu2) { ... } |
| 752 | void bar() const PW_SHARED_LOCKS_REQUIRED(mu1, mu2) { ... } |
| 753 | |
| 754 | .. cpp:function:: PW_LOCKS_EXCLUDED(...) |
| 755 | |
| 756 | Documents the locks acquired in the body of the function. These locks |
| 757 | cannot be held when calling this function (as Pigweed's default locks are |
| 758 | non-reentrant). |
| 759 | |
| 760 | Example: |
| 761 | |
| 762 | .. code-block:: cpp |
| 763 | |
| 764 | Mutex mu; |
| 765 | int a PW_GUARDED_BY(mu); |
| 766 | |
| 767 | void foo() PW_LOCKS_EXCLUDED(mu) { |
| 768 | mu.lock(); |
| 769 | ... |
| 770 | mu.unlock(); |
| 771 | } |
| 772 | |
| 773 | .. cpp:function:: PW_LOCK_RETURNED(...) |
| 774 | |
| 775 | Documents a function that returns a lock without acquiring it. For example, |
| 776 | a public getter method that returns a pointer to a private lock should |
| 777 | be annotated with ``PW_LOCK_RETURNED``. |
| 778 | |
| 779 | Example: |
| 780 | |
| 781 | .. code-block:: cpp |
| 782 | |
| 783 | class Foo { |
| 784 | public: |
| 785 | Mutex* mu() PW_LOCK_RETURNED(mu) { return μ } |
| 786 | |
| 787 | private: |
| 788 | Mutex mu; |
| 789 | }; |
| 790 | |
| 791 | .. cpp:function:: PW_NO_LOCK_SAFETY_ANALYSIS() |
| 792 | |
| 793 | Turns off thread safety checking within the body of a particular function. |
| 794 | This annotation is used to mark functions that are known to be correct, but |
| 795 | the locking behavior is more complicated than the analyzer can handle. |
| 796 | |
| 797 | Annotating Lock Objects |
| 798 | ^^^^^^^^^^^^^^^^^^^^^^^ |
| 799 | In order of lock usage annotation to work, the lock objects themselves need to |
| 800 | be annotated as well. In case you are providing your own lock or psuedo-lock |
| 801 | object, you can use the macros in this section to annotate it. |
| 802 | |
| 803 | As an example we've annotated a Lock and a RAII ScopedLocker object for you, see |
| 804 | the macro documentation after for more details: |
| 805 | |
| 806 | .. code-block:: cpp |
| 807 | |
| 808 | class PW_LOCKABLE("Lock") Lock { |
| 809 | public: |
| 810 | void Lock() PW_EXCLUSIVE_LOCK_FUNCTION(); |
| 811 | |
| 812 | void ReaderLock() PW_SHARED_LOCK_FUNCTION(); |
| 813 | |
| 814 | void Unlock() PW_UNLOCK_FUNCTION(); |
| 815 | |
| 816 | void ReaderUnlock() PW_SHARED_TRYLOCK_FUNCTION(); |
| 817 | |
| 818 | bool TryLock() PW_EXCLUSIVE_TRYLOCK_FUNCTION(true); |
| 819 | |
| 820 | bool ReaderTryLock() PW_SHARED_TRYLOCK_FUNCTION(true); |
| 821 | |
| 822 | void AssertHeld() PW_ASSERT_EXCLUSIVE_LOCK(); |
| 823 | |
| 824 | void AssertReaderHeld() PW_ASSERT_SHARED_LOCK(); |
| 825 | }; |
| 826 | |
| 827 | |
| 828 | // Tag types for selecting a constructor. |
| 829 | struct adopt_lock_t {} inline constexpr adopt_lock = {}; |
| 830 | struct defer_lock_t {} inline constexpr defer_lock = {}; |
| 831 | struct shared_lock_t {} inline constexpr shared_lock = {}; |
| 832 | |
| 833 | class PW_SCOPED_LOCKABLE ScopedLocker { |
| 834 | // Acquire lock, implicitly acquire *this and associate it with lock. |
| 835 | ScopedLocker(Lock *lock) PW_EXCLUSIVE_LOCK_FUNCTION(lock) |
| 836 | : lock_(lock), locked(true) { |
| 837 | lock->Lock(); |
| 838 | } |
| 839 | |
| 840 | // Assume lock is held, implicitly acquire *this and associate it with lock. |
| 841 | ScopedLocker(Lock *lock, adopt_lock_t) PW_EXCLUSIVE_LOCKS_REQUIRED(lock) |
| 842 | : lock_(lock), locked(true) {} |
| 843 | |
| 844 | // Acquire lock in shared mode, implicitly acquire *this and associate it |
| 845 | // with lock. |
| 846 | ScopedLocker(Lock *lock, shared_lock_t) PW_SHARED_LOCK_FUNCTION(lock) |
| 847 | : lock_(lock), locked(true) { |
| 848 | lock->ReaderLock(); |
| 849 | } |
| 850 | |
| 851 | // Assume lock is held in shared mode, implicitly acquire *this and associate |
| 852 | // it with lock. |
| 853 | ScopedLocker(Lock *lock, adopt_lock_t, shared_lock_t) |
| 854 | PW_SHARED_LOCKS_REQUIRED(lock) : lock_(lock), locked(true) {} |
| 855 | |
| 856 | // Assume lock is not held, implicitly acquire *this and associate it with |
| 857 | // lock. |
| 858 | ScopedLocker(Lock *lock, defer_lock_t) PW_LOCKS_EXCLUDED(lock) |
| 859 | : lock_(lock), locked(false) {} |
| 860 | |
| 861 | // Release *this and all associated locks, if they are still held. |
| 862 | // There is no warning if the scope was already unlocked before. |
| 863 | ~ScopedLocker() PW_UNLOCK_FUNCTION() { |
| 864 | if (locked) |
| 865 | lock_->GenericUnlock(); |
| 866 | } |
| 867 | |
| 868 | // Acquire all associated locks exclusively. |
| 869 | void Lock() PW_EXCLUSIVE_LOCK_FUNCTION() { |
| 870 | lock_->Lock(); |
| 871 | locked = true; |
| 872 | } |
| 873 | |
| 874 | // Try to acquire all associated locks exclusively. |
| 875 | bool TryLock() PW_EXCLUSIVE_TRYLOCK_FUNCTION(true) { |
| 876 | return locked = lock_->TryLock(); |
| 877 | } |
| 878 | |
| 879 | // Acquire all associated locks in shared mode. |
| 880 | void ReaderLock() PW_SHARED_LOCK_FUNCTION() { |
| 881 | lock_->ReaderLock(); |
| 882 | locked = true; |
| 883 | } |
| 884 | |
| 885 | // Try to acquire all associated locks in shared mode. |
| 886 | bool ReaderTryLock() PW_SHARED_TRYLOCK_FUNCTION(true) { |
| 887 | return locked = lock_->ReaderTryLock(); |
| 888 | } |
| 889 | |
| 890 | // Release all associated locks. Warn on double unlock. |
| 891 | void Unlock() PW_UNLOCK_FUNCTION() { |
| 892 | lock_->Unlock(); |
| 893 | locked = false; |
| 894 | } |
| 895 | |
| 896 | // Release all associated locks. Warn on double unlock. |
| 897 | void ReaderUnlock() PW_UNLOCK_FUNCTION() { |
| 898 | lock_->ReaderUnlock(); |
| 899 | locked = false; |
| 900 | } |
| 901 | |
| 902 | private: |
| 903 | Lock* lock_; |
| 904 | bool locked_; |
| 905 | }; |
| 906 | |
| 907 | .. cpp:function:: PW_LOCKABLE(name) |
| 908 | |
| 909 | Documents if a class/type is a lockable type (such as the ``pw::sync::Mutex`` |
| 910 | class). The name is used in the warning messages. This can also be useful on |
| 911 | classes which have locking like semantics but aren't actually locks. |
| 912 | |
| 913 | .. cpp:function:: PW_SCOPED_LOCKABLE() |
| 914 | |
| 915 | Documents if a class does RAII locking. The name is used in the warning |
| 916 | messages. |
| 917 | |
| 918 | The constructor should use ``LOCK_FUNCTION()`` to specify the lock that is |
| 919 | acquired, and the destructor should use ``UNLOCK_FUNCTION()`` with no |
| 920 | arguments; the analysis will assume that the destructor unlocks whatever the |
| 921 | constructor locked. |
| 922 | |
| 923 | .. cpp:function:: PW_EXCLUSIVE_LOCK_FUNCTION() |
| 924 | |
| 925 | Documents functions that acquire a lock in the body of a function, and do |
| 926 | not release it. |
| 927 | |
| 928 | .. cpp:function:: PW_SHARED_LOCK_FUNCTION() |
| 929 | |
| 930 | Documents functions that acquire a shared (reader) lock in the body of a |
| 931 | function, and do not release it. |
| 932 | |
| 933 | .. cpp:function:: PW_UNLOCK_FUNCTION() |
| 934 | |
| 935 | Documents functions that expect a lock to be held on entry to the function, |
| 936 | and release it in the body of the function. |
| 937 | |
| 938 | .. cpp:function:: PW_EXCLUSIVE_TRYLOCK_FUNCTION(try_success) |
| 939 | .. cpp:function:: PW_SHARED_TRYLOCK_FUNCTION(try_success) |
| 940 | |
| 941 | Documents functions that try to acquire a lock, and return success or failure |
| 942 | (or a non-boolean value that can be interpreted as a boolean). |
| 943 | The first argument should be ``true`` for functions that return ``true`` on |
| 944 | success, or ``false`` for functions that return `false` on success. The second |
| 945 | argument specifies the lock that is locked on success. If unspecified, this |
| 946 | lock is assumed to be ``this``. |
| 947 | |
| 948 | .. cpp:function:: PW_ASSERT_EXCLUSIVE_LOCK() |
| 949 | .. cpp:function:: PW_ASSERT_SHARED_LOCK() |
| 950 | |
| 951 | Documents functions that dynamically check to see if a lock is held, and fail |
| 952 | if it is not held. |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 953 | |
| 954 | -------------------- |
| 955 | Signaling Primitives |
| 956 | -------------------- |
| 957 | |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 958 | Native signaling primitives tend to vary more compared to critial section locks |
| 959 | across different platforms. For example, although common signaling primtives |
| 960 | like semaphores are in most if not all RTOSes and even POSIX, it was not in the |
| 961 | STL before C++20. Likewise many C++ developers are surprised that conditional |
| 962 | variables tend to not be natively supported on RTOSes. Although you can usually |
| 963 | build any signaling primitive based on other native signaling primitives, this |
| 964 | may come with non-trivial added overhead in ROM, RAM, and execution efficiency. |
| 965 | |
Ewout van Bekkum | f010606 | 2021-05-06 14:08:33 -0700 | [diff] [blame] | 966 | For this reason, Pigweed intends to provide some simpler signaling primitives |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 967 | which exist to solve a narrow programming need but can be implemented as |
| 968 | efficiently as possible for the platform that it is used on. |
| 969 | |
| 970 | This simpler but highly portable class of signaling primitives is intended to |
| 971 | ensure that a portability efficiency tradeoff does not have to be made up front. |
Ewout van Bekkum | f010606 | 2021-05-06 14:08:33 -0700 | [diff] [blame] | 972 | Today this is class of simpler signaling primitives is limited to the |
| 973 | ``pw::sync::ThreadNotification`` and ``pw::sync::TimedThreadNotification``. |
| 974 | |
| 975 | ThreadNotification |
| 976 | ================== |
| 977 | The ThreadNotification is a synchronization primitive that can be used to |
| 978 | permit a SINGLE thread to block and consume a latching, saturating |
| 979 | notification from multiple notifiers. |
| 980 | |
| 981 | .. Warning:: |
| 982 | This is a single consumer/waiter, multiple producer/notifier API! |
| 983 | The acquire APIs must only be invoked by a single consuming thread. As a |
| 984 | result, having multiple threads receiving notifications via the acquire API |
| 985 | is unsupported. |
| 986 | |
| 987 | This is effectively a subset of the ``pw::sync::BinarySemaphore`` API, except |
| 988 | that only a single thread can be notified and block at a time. |
| 989 | |
| 990 | The single consumer aspect of the API permits the use of a smaller and/or |
| 991 | faster native APIs such as direct thread signaling. This should be |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 992 | backed by the most efficient native primitive for a target, regardless of |
| 993 | whether that is a semaphore, event flag group, condition variable, or something |
| 994 | else. |
| 995 | |
Ewout van Bekkum | f010606 | 2021-05-06 14:08:33 -0700 | [diff] [blame] | 996 | Generic BinarySemaphore-based Backend |
| 997 | ------------------------------------- |
| 998 | This module provides a generic backend for ``pw::sync::ThreadNotification`` via |
| 999 | ``pw_sync:binary_semaphore_thread_notification`` which uses a |
| 1000 | ``pw::sync::BinarySemaphore`` as the backing primitive. See |
| 1001 | :ref:`BinarySemaphore <module-pw_sync-binary-semaphore>` for backend |
| 1002 | availability. |
| 1003 | |
| 1004 | Optimized Backend |
| 1005 | ----------------- |
| 1006 | .. list-table:: |
| 1007 | |
| 1008 | * - *Supported on* |
| 1009 | - *Optimized backend module* |
| 1010 | * - FreeRTOS |
| 1011 | - Planned |
| 1012 | * - ThreadX |
| 1013 | - Planned |
| 1014 | * - embOS |
| 1015 | - Planned |
| 1016 | * - STL |
| 1017 | - Not planned, use ``pw_sync:binary_semaphore_thread_notification`` |
| 1018 | * - Baremetal |
| 1019 | - Planned |
| 1020 | * - Zephyr |
| 1021 | - Planned |
| 1022 | * - CMSIS-RTOS API v2 & RTX5 |
| 1023 | - Planned |
| 1024 | |
| 1025 | C++ |
| 1026 | --- |
| 1027 | .. cpp:class:: pw::sync::ThreadNotification |
| 1028 | |
| 1029 | .. cpp:function:: void acquire() |
| 1030 | |
| 1031 | Blocks indefinitely until the thread is notified, i.e. until the |
| 1032 | notification latch can be cleared because it was set. |
| 1033 | |
| 1034 | Clears the notification latch. |
| 1035 | |
| 1036 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1037 | |
| 1038 | .. cpp:function:: bool try_acquire() |
| 1039 | |
| 1040 | Returns whether the thread has been notified, i.e. whether the notificion |
| 1041 | latch was set and resets the latch regardless. |
| 1042 | |
| 1043 | Clears the notification latch. |
| 1044 | |
| 1045 | Returns true if the thread was notified, meaning the the internal latch was |
| 1046 | reset successfully. |
| 1047 | |
| 1048 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1049 | |
| 1050 | .. cpp:function:: void release() |
| 1051 | |
| 1052 | Notifies the thread in a saturating manner, setting the notification latch. |
| 1053 | |
| 1054 | Raising the notification multiple time without it being acquired by the |
| 1055 | consuming thread is equivalent to raising the notification once to the |
| 1056 | thread. The notification is latched in case the thread was not waiting at |
| 1057 | the time. |
| 1058 | |
| 1059 | This is IRQ and thread safe. |
| 1060 | |
| 1061 | .. list-table:: |
| 1062 | |
| 1063 | * - *Safe to use in context* |
| 1064 | - *Thread* |
| 1065 | - *Interrupt* |
| 1066 | - *NMI* |
| 1067 | * - ``ThreadNotification::ThreadNotification`` |
| 1068 | - ✔ |
| 1069 | - |
| 1070 | - |
| 1071 | * - ``ThreadNotification::~ThreadNotification`` |
| 1072 | - ✔ |
| 1073 | - |
| 1074 | - |
| 1075 | * - ``void ThreadNotification::acquire`` |
| 1076 | - ✔ |
| 1077 | - |
| 1078 | - |
| 1079 | * - ``bool ThreadNotification::try_acquire`` |
| 1080 | - ✔ |
| 1081 | - |
| 1082 | - |
| 1083 | * - ``void ThreadNotification::release`` |
| 1084 | - ✔ |
| 1085 | - ✔ |
| 1086 | - |
| 1087 | |
| 1088 | Examples in C++ |
| 1089 | ^^^^^^^^^^^^^^^ |
| 1090 | .. code-block:: cpp |
| 1091 | |
| 1092 | #include "pw_sync/thread_notification.h" |
| 1093 | #include "pw_thread/thread_core.h" |
| 1094 | |
| 1095 | class FooHandler() : public pw::thread::ThreadCore { |
| 1096 | // Public API invoked by other threads and/or interrupts. |
| 1097 | void NewFooAvailable() { |
| 1098 | new_foo_notification_.release(); |
| 1099 | } |
| 1100 | |
| 1101 | private: |
| 1102 | pw::sync::ThreadNotification new_foo_notification_; |
| 1103 | |
| 1104 | // Thread function. |
| 1105 | void Run() override { |
| 1106 | while (true) { |
| 1107 | new_foo_notification_.acquire(); |
| 1108 | HandleFoo(); |
| 1109 | } |
| 1110 | } |
| 1111 | |
| 1112 | void HandleFoo(); |
| 1113 | } |
| 1114 | |
| 1115 | TimedThreadNotification |
| 1116 | ======================= |
| 1117 | The TimedThreadNotification is an extension of the ThreadNotification which |
| 1118 | offers timeout and deadline based semantics. |
| 1119 | |
| 1120 | .. Warning:: |
| 1121 | This is a single consumer/waiter, multiple producer/notifier API! |
| 1122 | The acquire APIs must only be invoked by a single consuming thread. As a |
| 1123 | result, having multiple threads receiving notifications via the acquire API |
| 1124 | is unsupported. |
| 1125 | |
| 1126 | Generic BinarySemaphore-based Backend |
| 1127 | ------------------------------------- |
| 1128 | This module provides a generic backend for ``pw::sync::TimedThreadNotification`` |
| 1129 | via ``pw_sync:binary_semaphore_timed_thread_notification`` which uses a |
| 1130 | ``pw::sync::BinarySemaphore`` as the backing primitive. See |
| 1131 | :ref:`BinarySemaphore <module-pw_sync-binary-semaphore>` for backend |
| 1132 | availability. |
| 1133 | |
| 1134 | Optimized Backend |
| 1135 | ----------------- |
| 1136 | .. list-table:: |
| 1137 | |
| 1138 | * - *Supported on* |
| 1139 | - *Backend module* |
| 1140 | * - FreeRTOS |
| 1141 | - Planned |
| 1142 | * - ThreadX |
| 1143 | - Planned |
| 1144 | * - embOS |
| 1145 | - Planned |
| 1146 | * - STL |
| 1147 | - Not planned, use ``pw_sync:binary_semaphore_thread_notification`` |
| 1148 | * - Zephyr |
| 1149 | - Planned |
| 1150 | * - CMSIS-RTOS API v2 & RTX5 |
| 1151 | - Planned |
| 1152 | |
| 1153 | C++ |
| 1154 | --- |
| 1155 | .. cpp:class:: pw::sync::TimedThreadNotification |
| 1156 | |
| 1157 | .. cpp:function:: void acquire() |
| 1158 | |
| 1159 | Blocks indefinitely until the thread is notified, i.e. until the |
| 1160 | notification latch can be cleared because it was set. |
| 1161 | |
| 1162 | Clears the notification latch. |
| 1163 | |
| 1164 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1165 | |
| 1166 | .. cpp:function:: bool try_acquire() |
| 1167 | |
| 1168 | Returns whether the thread has been notified, i.e. whether the notificion |
| 1169 | latch was set and resets the latch regardless. |
| 1170 | |
| 1171 | Clears the notification latch. |
| 1172 | |
| 1173 | Returns true if the thread was notified, meaning the the internal latch was |
| 1174 | reset successfully. |
| 1175 | |
| 1176 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1177 | |
| 1178 | .. cpp:function:: void release() |
| 1179 | |
| 1180 | Notifies the thread in a saturating manner, setting the notification latch. |
| 1181 | |
| 1182 | Raising the notification multiple time without it being acquired by the |
| 1183 | consuming thread is equivalent to raising the notification once to the |
| 1184 | thread. The notification is latched in case the thread was not waiting at |
| 1185 | the time. |
| 1186 | |
| 1187 | This is IRQ and thread safe. |
| 1188 | |
| 1189 | .. cpp:function:: bool try_acquire_for(chrono::SystemClock::duration timeout) |
| 1190 | |
| 1191 | Blocks until the specified timeout duration has elapsed or the thread |
| 1192 | has been notified (i.e. notification latch can be cleared because it was |
| 1193 | set), whichever comes first. |
| 1194 | |
| 1195 | Clears the notification latch. |
| 1196 | |
| 1197 | Returns true if the thread was notified, meaning the the internal latch was |
| 1198 | reset successfully. |
| 1199 | |
| 1200 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1201 | |
| 1202 | .. cpp:function:: bool try_acquire_until(chrono::SystemClock::time_point deadline) |
| 1203 | |
| 1204 | Blocks until the specified deadline time has been reached the thread has |
| 1205 | been notified (i.e. notification latch can be cleared because it was set), |
| 1206 | whichever comes first. |
| 1207 | |
| 1208 | Clears the notification latch. |
| 1209 | |
| 1210 | Returns true if the thread was notified, meaning the the internal latch was |
| 1211 | reset successfully. |
| 1212 | |
| 1213 | **IMPORTANT:** This should only be used by a single consumer thread. |
| 1214 | |
| 1215 | .. list-table:: |
| 1216 | |
| 1217 | * - *Safe to use in context* |
| 1218 | - *Thread* |
| 1219 | - *Interrupt* |
| 1220 | - *NMI* |
| 1221 | * - ``ThreadNotification::ThreadNotification`` |
| 1222 | - ✔ |
| 1223 | - |
| 1224 | - |
| 1225 | * - ``ThreadNotification::~ThreadNotification`` |
| 1226 | - ✔ |
| 1227 | - |
| 1228 | - |
| 1229 | * - ``void ThreadNotification::acquire`` |
| 1230 | - ✔ |
| 1231 | - |
| 1232 | - |
| 1233 | * - ``bool ThreadNotification::try_acquire`` |
| 1234 | - ✔ |
| 1235 | - |
| 1236 | - |
| 1237 | * - ``bool ThreadNotification::try_acquire_for`` |
| 1238 | - ✔ |
| 1239 | - |
| 1240 | - |
| 1241 | * - ``bool ThreadNotification::try_acquire_until`` |
| 1242 | - ✔ |
| 1243 | - |
| 1244 | - |
| 1245 | * - ``void ThreadNotification::release`` |
| 1246 | - ✔ |
| 1247 | - ✔ |
| 1248 | - |
| 1249 | |
| 1250 | Examples in C++ |
| 1251 | ^^^^^^^^^^^^^^^ |
| 1252 | .. code-block:: cpp |
| 1253 | |
| 1254 | #include "pw_sync/timed_thread_notification.h" |
| 1255 | #include "pw_thread/thread_core.h" |
| 1256 | |
| 1257 | class FooHandler() : public pw::thread::ThreadCore { |
| 1258 | // Public API invoked by other threads and/or interrupts. |
| 1259 | void NewFooAvailable() { |
| 1260 | new_foo_notification_.release(); |
| 1261 | } |
| 1262 | |
| 1263 | private: |
| 1264 | pw::sync::TimedThreadNotification new_foo_notification_; |
| 1265 | |
| 1266 | // Thread function. |
| 1267 | void Run() override { |
| 1268 | while (true) { |
| 1269 | if (new_foo_notification_.try_acquire_for(kNotificationTimeout)) { |
| 1270 | HandleFoo(); |
| 1271 | } |
| 1272 | DoOtherStuff(); |
| 1273 | } |
| 1274 | } |
| 1275 | |
| 1276 | void HandleFoo(); |
| 1277 | void DoOtherStuff(); |
| 1278 | } |
| 1279 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 1280 | CountingSemaphore |
| 1281 | ================= |
| 1282 | The CountingSemaphore is a synchronization primitive that can be used for |
| 1283 | counting events and/or resource management where receiver(s) can block on |
| 1284 | acquire until notifier(s) signal by invoking release. |
| 1285 | |
| 1286 | Note that unlike Mutexes, priority inheritance is not used by semaphores meaning |
| 1287 | semaphores are subject to unbounded priority inversions. Due to this, Pigweed |
| 1288 | does not recommend semaphores for mutual exclusion. |
| 1289 | |
| 1290 | The CountingSemaphore is initialized to being empty or having no tokens. |
| 1291 | |
| 1292 | The entire API is thread safe, but only a subset is interrupt safe. None of it |
| 1293 | is NMI safe. |
| 1294 | |
| 1295 | .. Warning:: |
| 1296 | Releasing multiple tokens is often not natively supported, meaning you may |
| 1297 | end up invoking the native kernel API many times, i.e. once per token you |
| 1298 | are releasing! |
| 1299 | |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 1300 | .. list-table:: |
| 1301 | |
| 1302 | * - *Supported on* |
| 1303 | - *Backend module* |
| 1304 | * - FreeRTOS |
| 1305 | - :ref:`module-pw_sync_freertos` |
| 1306 | * - ThreadX |
| 1307 | - :ref:`module-pw_sync_threadx` |
| 1308 | * - embOS |
| 1309 | - :ref:`module-pw_sync_embos` |
| 1310 | * - STL |
| 1311 | - :ref:`module-pw_sync_stl` |
| 1312 | * - Zephyr |
| 1313 | - Planned |
| 1314 | * - CMSIS-RTOS API v2 & RTX5 |
| 1315 | - Planned |
| 1316 | |
Ewout van Bekkum | f010606 | 2021-05-06 14:08:33 -0700 | [diff] [blame] | 1317 | .. _module-pw_sync-binary-semaphore: |
| 1318 | |
Ewout van Bekkum | f84638b | 2021-03-12 16:09:08 -0800 | [diff] [blame] | 1319 | BinarySemaphore |
| 1320 | =============== |
| 1321 | BinarySemaphore is a specialization of CountingSemaphore with an arbitrary token |
| 1322 | limit of 1. Note that that ``max()`` is >= 1, meaning it may be released up to |
| 1323 | ``max()`` times but only acquired once for those N releases. |
| 1324 | |
| 1325 | Implementations of BinarySemaphore are typically more efficient than the |
| 1326 | default implementation of CountingSemaphore. |
| 1327 | |
| 1328 | The BinarySemaphore is initialized to being empty or having no tokens. |
| 1329 | |
| 1330 | The entire API is thread safe, but only a subset is interrupt safe. None of it |
| 1331 | is NMI safe. |
Ewout van Bekkum | 3b9eca4 | 2021-04-02 14:54:02 -0700 | [diff] [blame] | 1332 | |
| 1333 | .. list-table:: |
| 1334 | |
| 1335 | * - *Supported on* |
| 1336 | - *Backend module* |
| 1337 | * - FreeRTOS |
| 1338 | - :ref:`module-pw_sync_freertos` |
| 1339 | * - ThreadX |
| 1340 | - :ref:`module-pw_sync_threadx` |
| 1341 | * - embOS |
| 1342 | - :ref:`module-pw_sync_embos` |
| 1343 | * - STL |
| 1344 | - :ref:`module-pw_sync_stl` |
| 1345 | * - Zephyr |
| 1346 | - Planned |
| 1347 | * - CMSIS-RTOS API v2 & RTX5 |
| 1348 | - Planned |
| 1349 | |
Ewout van Bekkum | cc756c8 | 2021-05-12 07:57:43 -0700 | [diff] [blame] | 1350 | Conditional Variables |
| 1351 | ===================== |
| 1352 | We've decided for now to skip on conditional variables. These are constructs, |
| 1353 | which are typically not natively available on RTOSes. CVs would have to be |
| 1354 | backed by a multiple hidden semaphore(s) in addition to the explicit public |
| 1355 | mutex. In other words a CV typically ends up as a a composition of |
| 1356 | synchronization primitives on RTOSes. That being said, one could implement them |
| 1357 | using our semaphore and mutex layers and we may consider providing this in the |
| 1358 | future. However for most of our resource constrained customers they will mostly |
| 1359 | likely be using semaphores more often than CVs. |