| |
| :mod:`threading` --- Higher-level threading interface |
| ===================================================== |
| |
| .. module:: threading |
| :synopsis: Higher-level threading interface. |
| |
| |
| This module constructs higher-level threading interfaces on top of the lower |
| level :mod:`thread` module. |
| |
| The :mod:`dummy_threading` module is provided for situations where |
| :mod:`threading` cannot be used because :mod:`thread` is missing. |
| |
| This module defines the following functions and objects: |
| |
| |
| .. function:: activeCount() |
| |
| Return the number of :class:`Thread` objects currently alive. The returned |
| count is equal to the length of the list returned by :func:`enumerate`. |
| |
| |
| .. function:: Condition() |
| :noindex: |
| |
| A factory function that returns a new condition variable object. A condition |
| variable allows one or more threads to wait until they are notified by another |
| thread. |
| |
| |
| .. function:: currentThread() |
| |
| Return the current :class:`Thread` object, corresponding to the caller's thread |
| of control. If the caller's thread of control was not created through the |
| :mod:`threading` module, a dummy thread object with limited functionality is |
| returned. |
| |
| |
| .. function:: enumerate() |
| |
| Return a list of all :class:`Thread` objects currently alive. The list includes |
| daemonic threads, dummy thread objects created by :func:`currentThread`, and the |
| main thread. It excludes terminated threads and threads that have not yet been |
| started. |
| |
| |
| .. function:: Event() |
| :noindex: |
| |
| A factory function that returns a new event object. An event manages a flag |
| that can be set to true with the :meth:`set` method and reset to false with the |
| :meth:`clear` method. The :meth:`wait` method blocks until the flag is true. |
| |
| |
| .. class:: local |
| |
| A class that represents thread-local data. Thread-local data are data whose |
| values are thread specific. To manage thread-local data, just create an |
| instance of :class:`local` (or a subclass) and store attributes on it:: |
| |
| mydata = threading.local() |
| mydata.x = 1 |
| |
| The instance's values will be different for separate threads. |
| |
| For more details and extensive examples, see the documentation string of the |
| :mod:`_threading_local` module. |
| |
| |
| .. function:: Lock() |
| |
| A factory function that returns a new primitive lock object. Once a thread has |
| acquired it, subsequent attempts to acquire it block, until it is released; any |
| thread may release it. |
| |
| |
| .. function:: RLock() |
| |
| A factory function that returns a new reentrant lock object. A reentrant lock |
| must be released by the thread that acquired it. Once a thread has acquired a |
| reentrant lock, the same thread may acquire it again without blocking; the |
| thread must release it once for each time it has acquired it. |
| |
| |
| .. function:: Semaphore([value]) |
| :noindex: |
| |
| A factory function that returns a new semaphore object. A semaphore manages a |
| counter representing the number of :meth:`release` calls minus the number of |
| :meth:`acquire` calls, plus an initial value. The :meth:`acquire` method blocks |
| if necessary until it can return without making the counter negative. If not |
| given, *value* defaults to 1. |
| |
| |
| .. function:: BoundedSemaphore([value]) |
| |
| A factory function that returns a new bounded semaphore object. A bounded |
| semaphore checks to make sure its current value doesn't exceed its initial |
| value. If it does, :exc:`ValueError` is raised. In most situations semaphores |
| are used to guard resources with limited capacity. If the semaphore is released |
| too many times it's a sign of a bug. If not given, *value* defaults to 1. |
| |
| |
| .. class:: Thread |
| |
| A class that represents a thread of control. This class can be safely |
| subclassed in a limited fashion. |
| |
| |
| .. class:: Timer |
| |
| A thread that executes a function after a specified interval has passed. |
| |
| |
| .. function:: settrace(func) |
| |
| .. index:: single: trace function |
| |
| Set a trace function for all threads started from the :mod:`threading` module. |
| The *func* will be passed to :func:`sys.settrace` for each thread, before its |
| :meth:`run` method is called. |
| |
| |
| .. function:: setprofile(func) |
| |
| .. index:: single: profile function |
| |
| Set a profile function for all threads started from the :mod:`threading` module. |
| The *func* will be passed to :func:`sys.setprofile` for each thread, before its |
| :meth:`run` method is called. |
| |
| |
| .. function:: stack_size([size]) |
| |
| Return the thread stack size used when creating new threads. The optional |
| *size* argument specifies the stack size to be used for subsequently created |
| threads, and must be 0 (use platform or configured default) or a positive |
| integer value of at least 32,768 (32kB). If changing the thread stack size is |
| unsupported, a :exc:`ThreadError` is raised. If the specified stack size is |
| invalid, a :exc:`ValueError` is raised and the stack size is unmodified. 32kB |
| is currently the minimum supported stack size value to guarantee sufficient |
| stack space for the interpreter itself. Note that some platforms may have |
| particular restrictions on values for the stack size, such as requiring a |
| minimum stack size > 32kB or requiring allocation in multiples of the system |
| memory page size - platform documentation should be referred to for more |
| information (4kB pages are common; using multiples of 4096 for the stack size is |
| the suggested approach in the absence of more specific information). |
| Availability: Windows, systems with POSIX threads. |
| |
| |
| Detailed interfaces for the objects are documented below. |
| |
| The design of this module is loosely based on Java's threading model. However, |
| where Java makes locks and condition variables basic behavior of every object, |
| they are separate objects in Python. Python's :class:`Thread` class supports a |
| subset of the behavior of Java's Thread class; currently, there are no |
| priorities, no thread groups, and threads cannot be destroyed, stopped, |
| suspended, resumed, or interrupted. The static methods of Java's Thread class, |
| when implemented, are mapped to module-level functions. |
| |
| All of the methods described below are executed atomically. |
| |
| |
| .. _lock-objects: |
| |
| Lock Objects |
| ------------ |
| |
| A primitive lock is a synchronization primitive that is not owned by a |
| particular thread when locked. In Python, it is currently the lowest level |
| synchronization primitive available, implemented directly by the :mod:`thread` |
| extension module. |
| |
| A primitive lock is in one of two states, "locked" or "unlocked". It is created |
| in the unlocked state. It has two basic methods, :meth:`acquire` and |
| :meth:`release`. When the state is unlocked, :meth:`acquire` changes the state |
| to locked and returns immediately. When the state is locked, :meth:`acquire` |
| blocks until a call to :meth:`release` in another thread changes it to unlocked, |
| then the :meth:`acquire` call resets it to locked and returns. The |
| :meth:`release` method should only be called in the locked state; it changes the |
| state to unlocked and returns immediately. If an attempt is made to release an |
| unlocked lock, a :exc:`RuntimeError` will be raised. |
| |
| When more than one thread is blocked in :meth:`acquire` waiting for the state to |
| turn to unlocked, only one thread proceeds when a :meth:`release` call resets |
| the state to unlocked; which one of the waiting threads proceeds is not defined, |
| and may vary across implementations. |
| |
| All methods are executed atomically. |
| |
| |
| .. method:: Lock.acquire([blocking=1]) |
| |
| Acquire a lock, blocking or non-blocking. |
| |
| When invoked without arguments, block until the lock is unlocked, then set it to |
| locked, and return true. |
| |
| When invoked with the *blocking* argument set to true, do the same thing as when |
| called without arguments, and return true. |
| |
| When invoked with the *blocking* argument set to false, do not block. If a call |
| without an argument would block, return false immediately; otherwise, do the |
| same thing as when called without arguments, and return true. |
| |
| |
| .. method:: Lock.release() |
| |
| Release a lock. |
| |
| When the lock is locked, reset it to unlocked, and return. If any other threads |
| are blocked waiting for the lock to become unlocked, allow exactly one of them |
| to proceed. |
| |
| Do not call this method when the lock is unlocked. |
| |
| There is no return value. |
| |
| |
| .. _rlock-objects: |
| |
| RLock Objects |
| ------------- |
| |
| A reentrant lock is a synchronization primitive that may be acquired multiple |
| times by the same thread. Internally, it uses the concepts of "owning thread" |
| and "recursion level" in addition to the locked/unlocked state used by primitive |
| locks. In the locked state, some thread owns the lock; in the unlocked state, |
| no thread owns it. |
| |
| To lock the lock, a thread calls its :meth:`acquire` method; this returns once |
| the thread owns the lock. To unlock the lock, a thread calls its |
| :meth:`release` method. :meth:`acquire`/:meth:`release` call pairs may be |
| nested; only the final :meth:`release` (the :meth:`release` of the outermost |
| pair) resets the lock to unlocked and allows another thread blocked in |
| :meth:`acquire` to proceed. |
| |
| |
| .. method:: RLock.acquire([blocking=1]) |
| |
| Acquire a lock, blocking or non-blocking. |
| |
| When invoked without arguments: if this thread already owns the lock, increment |
| the recursion level by one, and return immediately. Otherwise, if another |
| thread owns the lock, block until the lock is unlocked. Once the lock is |
| unlocked (not owned by any thread), then grab ownership, set the recursion level |
| to one, and return. If more than one thread is blocked waiting until the lock |
| is unlocked, only one at a time will be able to grab ownership of the lock. |
| There is no return value in this case. |
| |
| When invoked with the *blocking* argument set to true, do the same thing as when |
| called without arguments, and return true. |
| |
| When invoked with the *blocking* argument set to false, do not block. If a call |
| without an argument would block, return false immediately; otherwise, do the |
| same thing as when called without arguments, and return true. |
| |
| |
| .. method:: RLock.release() |
| |
| Release a lock, decrementing the recursion level. If after the decrement it is |
| zero, reset the lock to unlocked (not owned by any thread), and if any other |
| threads are blocked waiting for the lock to become unlocked, allow exactly one |
| of them to proceed. If after the decrement the recursion level is still |
| nonzero, the lock remains locked and owned by the calling thread. |
| |
| Only call this method when the calling thread owns the lock. A |
| :exc:`RuntimeError` is raised if this method is called when the lock is |
| unlocked. |
| |
| There is no return value. |
| |
| |
| .. _condition-objects: |
| |
| Condition Objects |
| ----------------- |
| |
| A condition variable is always associated with some kind of lock; this can be |
| passed in or one will be created by default. (Passing one in is useful when |
| several condition variables must share the same lock.) |
| |
| A condition variable has :meth:`acquire` and :meth:`release` methods that call |
| the corresponding methods of the associated lock. It also has a :meth:`wait` |
| method, and :meth:`notify` and :meth:`notifyAll` methods. These three must only |
| be called when the calling thread has acquired the lock, otherwise a |
| :exc:`RuntimeError` is raised. |
| |
| The :meth:`wait` method releases the lock, and then blocks until it is awakened |
| by a :meth:`notify` or :meth:`notifyAll` call for the same condition variable in |
| another thread. Once awakened, it re-acquires the lock and returns. It is also |
| possible to specify a timeout. |
| |
| The :meth:`notify` method wakes up one of the threads waiting for the condition |
| variable, if any are waiting. The :meth:`notifyAll` method wakes up all threads |
| waiting for the condition variable. |
| |
| Note: the :meth:`notify` and :meth:`notifyAll` methods don't release the lock; |
| this means that the thread or threads awakened will not return from their |
| :meth:`wait` call immediately, but only when the thread that called |
| :meth:`notify` or :meth:`notifyAll` finally relinquishes ownership of the lock. |
| |
| Tip: the typical programming style using condition variables uses the lock to |
| synchronize access to some shared state; threads that are interested in a |
| particular change of state call :meth:`wait` repeatedly until they see the |
| desired state, while threads that modify the state call :meth:`notify` or |
| :meth:`notifyAll` when they change the state in such a way that it could |
| possibly be a desired state for one of the waiters. For example, the following |
| code is a generic producer-consumer situation with unlimited buffer capacity:: |
| |
| # Consume one item |
| cv.acquire() |
| while not an_item_is_available(): |
| cv.wait() |
| get_an_available_item() |
| cv.release() |
| |
| # Produce one item |
| cv.acquire() |
| make_an_item_available() |
| cv.notify() |
| cv.release() |
| |
| To choose between :meth:`notify` and :meth:`notifyAll`, consider whether one |
| state change can be interesting for only one or several waiting threads. E.g. |
| in a typical producer-consumer situation, adding one item to the buffer only |
| needs to wake up one consumer thread. |
| |
| |
| .. class:: Condition([lock]) |
| |
| If the *lock* argument is given and not ``None``, it must be a :class:`Lock` or |
| :class:`RLock` object, and it is used as the underlying lock. Otherwise, a new |
| :class:`RLock` object is created and used as the underlying lock. |
| |
| |
| .. method:: Condition.acquire(*args) |
| |
| Acquire the underlying lock. This method calls the corresponding method on the |
| underlying lock; the return value is whatever that method returns. |
| |
| |
| .. method:: Condition.release() |
| |
| Release the underlying lock. This method calls the corresponding method on the |
| underlying lock; there is no return value. |
| |
| |
| .. method:: Condition.wait([timeout]) |
| |
| Wait until notified or until a timeout occurs. If the calling thread has not |
| acquired the lock when this method is called, a :exc:`RuntimeError` is raised. |
| |
| This method releases the underlying lock, and then blocks until it is awakened |
| by a :meth:`notify` or :meth:`notifyAll` call for the same condition variable in |
| another thread, or until the optional timeout occurs. Once awakened or timed |
| out, it re-acquires the lock and returns. |
| |
| When the *timeout* argument is present and not ``None``, it should be a floating |
| point number specifying a timeout for the operation in seconds (or fractions |
| thereof). |
| |
| When the underlying lock is an :class:`RLock`, it is not released using its |
| :meth:`release` method, since this may not actually unlock the lock when it was |
| acquired multiple times recursively. Instead, an internal interface of the |
| :class:`RLock` class is used, which really unlocks it even when it has been |
| recursively acquired several times. Another internal interface is then used to |
| restore the recursion level when the lock is reacquired. |
| |
| |
| .. method:: Condition.notify() |
| |
| Wake up a thread waiting on this condition, if any. Wait until notified or until |
| a timeout occurs. If the calling thread has not acquired the lock when this |
| method is called, a :exc:`RuntimeError` is raised. |
| |
| This method wakes up one of the threads waiting for the condition variable, if |
| any are waiting; it is a no-op if no threads are waiting. |
| |
| The current implementation wakes up exactly one thread, if any are waiting. |
| However, it's not safe to rely on this behavior. A future, optimized |
| implementation may occasionally wake up more than one thread. |
| |
| Note: the awakened thread does not actually return from its :meth:`wait` call |
| until it can reacquire the lock. Since :meth:`notify` does not release the |
| lock, its caller should. |
| |
| |
| .. method:: Condition.notifyAll() |
| |
| Wake up all threads waiting on this condition. This method acts like |
| :meth:`notify`, but wakes up all waiting threads instead of one. If the calling |
| thread has not acquired the lock when this method is called, a |
| :exc:`RuntimeError` is raised. |
| |
| |
| .. _semaphore-objects: |
| |
| Semaphore Objects |
| ----------------- |
| |
| This is one of the oldest synchronization primitives in the history of computer |
| science, invented by the early Dutch computer scientist Edsger W. Dijkstra (he |
| used :meth:`P` and :meth:`V` instead of :meth:`acquire` and :meth:`release`). |
| |
| A semaphore manages an internal counter which is decremented by each |
| :meth:`acquire` call and incremented by each :meth:`release` call. The counter |
| can never go below zero; when :meth:`acquire` finds that it is zero, it blocks, |
| waiting until some other thread calls :meth:`release`. |
| |
| |
| .. class:: Semaphore([value]) |
| |
| The optional argument gives the initial *value* for the internal counter; it |
| defaults to ``1``. If the *value* given is less than 0, :exc:`ValueError` is |
| raised. |
| |
| |
| .. method:: Semaphore.acquire([blocking]) |
| |
| Acquire a semaphore. |
| |
| When invoked without arguments: if the internal counter is larger than zero on |
| entry, decrement it by one and return immediately. If it is zero on entry, |
| block, waiting until some other thread has called :meth:`release` to make it |
| larger than zero. This is done with proper interlocking so that if multiple |
| :meth:`acquire` calls are blocked, :meth:`release` will wake exactly one of them |
| up. The implementation may pick one at random, so the order in which blocked |
| threads are awakened should not be relied on. There is no return value in this |
| case. |
| |
| When invoked with *blocking* set to true, do the same thing as when called |
| without arguments, and return true. |
| |
| When invoked with *blocking* set to false, do not block. If a call without an |
| argument would block, return false immediately; otherwise, do the same thing as |
| when called without arguments, and return true. |
| |
| |
| .. method:: Semaphore.release() |
| |
| Release a semaphore, incrementing the internal counter by one. When it was zero |
| on entry and another thread is waiting for it to become larger than zero again, |
| wake up that thread. |
| |
| |
| .. _semaphore-examples: |
| |
| :class:`Semaphore` Example |
| ^^^^^^^^^^^^^^^^^^^^^^^^^^ |
| |
| Semaphores are often used to guard resources with limited capacity, for example, |
| a database server. In any situation where the size of the resource size is |
| fixed, you should use a bounded semaphore. Before spawning any worker threads, |
| your main thread would initialize the semaphore:: |
| |
| maxconnections = 5 |
| ... |
| pool_sema = BoundedSemaphore(value=maxconnections) |
| |
| Once spawned, worker threads call the semaphore's acquire and release methods |
| when they need to connect to the server:: |
| |
| pool_sema.acquire() |
| conn = connectdb() |
| ... use connection ... |
| conn.close() |
| pool_sema.release() |
| |
| The use of a bounded semaphore reduces the chance that a programming error which |
| causes the semaphore to be released more than it's acquired will go undetected. |
| |
| |
| .. _event-objects: |
| |
| Event Objects |
| ------------- |
| |
| This is one of the simplest mechanisms for communication between threads: one |
| thread signals an event and other threads wait for it. |
| |
| An event object manages an internal flag that can be set to true with the |
| :meth:`set` method and reset to false with the :meth:`clear` method. The |
| :meth:`wait` method blocks until the flag is true. |
| |
| |
| .. class:: Event() |
| |
| The internal flag is initially false. |
| |
| |
| .. method:: Event.isSet() |
| |
| Return true if and only if the internal flag is true. |
| |
| |
| .. method:: Event.set() |
| |
| Set the internal flag to true. All threads waiting for it to become true are |
| awakened. Threads that call :meth:`wait` once the flag is true will not block at |
| all. |
| |
| |
| .. method:: Event.clear() |
| |
| Reset the internal flag to false. Subsequently, threads calling :meth:`wait` |
| will block until :meth:`set` is called to set the internal flag to true again. |
| |
| |
| .. method:: Event.wait([timeout]) |
| |
| Block until the internal flag is true. If the internal flag is true on entry, |
| return immediately. Otherwise, block until another thread calls :meth:`set` to |
| set the flag to true, or until the optional timeout occurs. |
| |
| When the timeout argument is present and not ``None``, it should be a floating |
| point number specifying a timeout for the operation in seconds (or fractions |
| thereof). |
| |
| |
| .. _thread-objects: |
| |
| Thread Objects |
| -------------- |
| |
| This class represents an activity that is run in a separate thread of control. |
| There are two ways to specify the activity: by passing a callable object to the |
| constructor, or by overriding the :meth:`run` method in a subclass. No other |
| methods (except for the constructor) should be overridden in a subclass. In |
| other words, *only* override the :meth:`__init__` and :meth:`run` methods of |
| this class. |
| |
| Once a thread object is created, its activity must be started by calling the |
| thread's :meth:`start` method. This invokes the :meth:`run` method in a |
| separate thread of control. |
| |
| Once the thread's activity is started, the thread is considered 'alive'. It |
| stops being alive when its :meth:`run` method terminates -- either normally, or |
| by raising an unhandled exception. The :meth:`isAlive` method tests whether the |
| thread is alive. |
| |
| Other threads can call a thread's :meth:`join` method. This blocks the calling |
| thread until the thread whose :meth:`join` method is called is terminated. |
| |
| A thread has a name. The name can be passed to the constructor, set with the |
| :meth:`setName` method, and retrieved with the :meth:`getName` method. |
| |
| A thread can be flagged as a "daemon thread". The significance of this flag is |
| that the entire Python program exits when only daemon threads are left. The |
| initial value is inherited from the creating thread. The flag can be set with |
| the :meth:`setDaemon` method and retrieved with the :meth:`isDaemon` method. |
| |
| There is a "main thread" object; this corresponds to the initial thread of |
| control in the Python program. It is not a daemon thread. |
| |
| There is the possibility that "dummy thread objects" are created. These are |
| thread objects corresponding to "alien threads", which are threads of control |
| started outside the threading module, such as directly from C code. Dummy |
| thread objects have limited functionality; they are always considered alive and |
| daemonic, and cannot be :meth:`join`\ ed. They are never deleted, since it is |
| impossible to detect the termination of alien threads. |
| |
| |
| .. class:: Thread(group=None, target=None, name=None, args=(), kwargs={}) |
| |
| This constructor should always be called with keyword arguments. Arguments are: |
| |
| *group* should be ``None``; reserved for future extension when a |
| :class:`ThreadGroup` class is implemented. |
| |
| *target* is the callable object to be invoked by the :meth:`run` method. |
| Defaults to ``None``, meaning nothing is called. |
| |
| *name* is the thread name. By default, a unique name is constructed of the form |
| "Thread-*N*" where *N* is a small decimal number. |
| |
| *args* is the argument tuple for the target invocation. Defaults to ``()``. |
| |
| *kwargs* is a dictionary of keyword arguments for the target invocation. |
| Defaults to ``{}``. |
| |
| If the subclass overrides the constructor, it must make sure to invoke the base |
| class constructor (``Thread.__init__()``) before doing anything else to the |
| thread. |
| |
| |
| .. method:: Thread.start() |
| |
| Start the thread's activity. |
| |
| It must be called at most once per thread object. It arranges for the object's |
| :meth:`run` method to be invoked in a separate thread of control. |
| |
| This method will raise a :exc:`RuntimeException` if called more than once on the |
| same thread object. |
| |
| |
| .. method:: Thread.run() |
| |
| Method representing the thread's activity. |
| |
| You may override this method in a subclass. The standard :meth:`run` method |
| invokes the callable object passed to the object's constructor as the *target* |
| argument, if any, with sequential and keyword arguments taken from the *args* |
| and *kwargs* arguments, respectively. |
| |
| |
| .. method:: Thread.join([timeout]) |
| |
| Wait until the thread terminates. This blocks the calling thread until the |
| thread whose :meth:`join` method is called terminates -- either normally or |
| through an unhandled exception -- or until the optional timeout occurs. |
| |
| When the *timeout* argument is present and not ``None``, it should be a floating |
| point number specifying a timeout for the operation in seconds (or fractions |
| thereof). As :meth:`join` always returns ``None``, you must call |
| :meth:`isAlive` to decide whether a timeout happened. |
| |
| When the *timeout* argument is not present or ``None``, the operation will block |
| until the thread terminates. |
| |
| A thread can be :meth:`join`\ ed many times. |
| |
| :meth:`join` may throw a :exc:`RuntimeError`, if an attempt is made to join the |
| current thread as that would cause a deadlock. It is also an error to |
| :meth:`join` a thread before it has been started and attempts to do so raises |
| same exception. |
| |
| |
| .. method:: Thread.getName() |
| |
| Return the thread's name. |
| |
| |
| .. method:: Thread.setName(name) |
| |
| Set the thread's name. |
| |
| The name is a string used for identification purposes only. It has no semantics. |
| Multiple threads may be given the same name. The initial name is set by the |
| constructor. |
| |
| |
| .. method:: Thread.isAlive() |
| |
| Return whether the thread is alive. |
| |
| Roughly, a thread is alive from the moment the :meth:`start` method returns |
| until its :meth:`run` method terminates. The module function :func:`enumerate` |
| returns a list of all alive threads. |
| |
| |
| .. method:: Thread.isDaemon() |
| |
| Return the thread's daemon flag. |
| |
| |
| .. method:: Thread.setDaemon(daemonic) |
| |
| Set the thread's daemon flag to the Boolean value *daemonic*. This must be |
| called before :meth:`start` is called, otherwise :exc:`RuntimeError` is raised. |
| |
| The initial value is inherited from the creating thread. |
| |
| The entire Python program exits when no alive non-daemon threads are left. |
| |
| |
| .. _timer-objects: |
| |
| Timer Objects |
| ------------- |
| |
| This class represents an action that should be run only after a certain amount |
| of time has passed --- a timer. :class:`Timer` is a subclass of :class:`Thread` |
| and as such also functions as an example of creating custom threads. |
| |
| Timers are started, as with threads, by calling their :meth:`start` method. The |
| timer can be stopped (before its action has begun) by calling the :meth:`cancel` |
| method. The interval the timer will wait before executing its action may not be |
| exactly the same as the interval specified by the user. |
| |
| For example:: |
| |
| def hello(): |
| print "hello, world" |
| |
| t = Timer(30.0, hello) |
| t.start() # after 30 seconds, "hello, world" will be printed |
| |
| |
| .. class:: Timer(interval, function, args=[], kwargs={}) |
| |
| Create a timer that will run *function* with arguments *args* and keyword |
| arguments *kwargs*, after *interval* seconds have passed. |
| |
| |
| .. method:: Timer.cancel() |
| |
| Stop the timer, and cancel the execution of the timer's action. This will only |
| work if the timer is still in its waiting stage. |
| |
| |
| .. _with-locks: |
| |
| Using locks, conditions, and semaphores in the :keyword:`with` statement |
| ------------------------------------------------------------------------ |
| |
| All of the objects provided by this module that have :meth:`acquire` and |
| :meth:`release` methods can be used as context managers for a :keyword:`with` |
| statement. The :meth:`acquire` method will be called when the block is entered, |
| and :meth:`release` will be called when the block is exited. |
| |
| Currently, :class:`Lock`, :class:`RLock`, :class:`Condition`, |
| :class:`Semaphore`, and :class:`BoundedSemaphore` objects may be used as |
| :keyword:`with` statement context managers. For example:: |
| |
| from __future__ import with_statement |
| import threading |
| |
| some_rlock = threading.RLock() |
| |
| with some_rlock: |
| print "some_rlock is locked while this executes" |
| |