Modernize SkMutex and SkSemaphore.
- use <atomic>
- fuse SkMutex and SkBaseMutex
- fuse SkSemaphore and SkBaseSemaphore
Still TODO:
- replace SK_DECLARE_STATIC_MUTEX(name) with static SkMutex name
I just didn't want to bother fixing all that up until I know this CL sticks.
BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1947153002
No public API changes.
TBR=reed@google.com
Committed: https://skia.googlesource.com/skia/+/427c2819d9237d7d7729c59238036cfc73c072ea
Review-Url: https://codereview.chromium.org/1947153002
diff --git a/include/ports/SkFontConfigInterface.h b/include/ports/SkFontConfigInterface.h
index 72cad0a..9f98e35 100644
--- a/include/ports/SkFontConfigInterface.h
+++ b/include/ports/SkFontConfigInterface.h
@@ -13,7 +13,6 @@
#include "SkRefCnt.h"
#include "SkTypeface.h"
-struct SkBaseMutex;
class SkFontMgr;
/**
diff --git a/include/private/SkMutex.h b/include/private/SkMutex.h
index 8c78e12..3b0e1c4 100644
--- a/include/private/SkMutex.h
+++ b/include/private/SkMutex.h
@@ -8,33 +8,16 @@
#ifndef SkMutex_DEFINED
#define SkMutex_DEFINED
-// This file is not part of the public Skia API.
#include "../private/SkSemaphore.h"
+#include "../private/SkThreadID.h"
#include "SkTypes.h"
-#ifdef SK_DEBUG
- #include "../private/SkThreadID.h"
-#endif
+#define SK_DECLARE_STATIC_MUTEX(name) static SkBaseMutex name;
-#define SK_MUTEX_SEMAPHORE_INIT {1, {0}}
+class SkBaseMutex {
+public:
+ constexpr SkBaseMutex() = default;
-#ifdef SK_DEBUG
- #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT, 0}
-#else
- #define SK_BASE_MUTEX_INIT {SK_MUTEX_SEMAPHORE_INIT}
-#endif
-
-// Using POD-style initialization prevents the generation of a static initializer.
-//
-// Without magic statics there are no thread safety guarantees on initialization
-// of local statics (even POD). As a result, it is illegal to use
-// SK_DECLARE_STATIC_MUTEX in a function.
-//
-// Because SkBaseMutex is not a primitive, a static SkBaseMutex cannot be
-// initialized in a class with this macro.
-#define SK_DECLARE_STATIC_MUTEX(name) namespace {} static SkBaseMutex name = SK_BASE_MUTEX_INIT;
-
-struct SkBaseMutex {
void acquire() {
fSemaphore.wait();
SkDEBUGCODE(fOwner = SkGetThreadID();)
@@ -50,20 +33,15 @@
SkASSERT(fOwner == SkGetThreadID());
}
- SkBaseSemaphore fSemaphore;
- SkDEBUGCODE(SkThreadID fOwner;)
+protected:
+ SkBaseSemaphore fSemaphore{1};
+ SkDEBUGCODE(SkThreadID fOwner{kIllegalThreadID};)
};
-// This needs to use subclassing instead of encapsulation to make SkAutoMutexAcquire to work.
class SkMutex : public SkBaseMutex {
public:
- SkMutex () {
- fSemaphore = SK_MUTEX_SEMAPHORE_INIT;
- SkDEBUGCODE(fOwner = kIllegalThreadID);
- }
- ~SkMutex () { fSemaphore.deleteSemaphore(); }
- SkMutex(const SkMutex&) = delete;
- SkMutex& operator=(const SkMutex&) = delete;
+ using SkBaseMutex::SkBaseMutex;
+ ~SkMutex() { fSemaphore.cleanup(); }
};
template <typename Lock>
diff --git a/include/private/SkSemaphore.h b/include/private/SkSemaphore.h
index cb2f58d..3da2b99 100644
--- a/include/private/SkSemaphore.h
+++ b/include/private/SkSemaphore.h
@@ -8,43 +8,27 @@
#ifndef SkSemaphore_DEFINED
#define SkSemaphore_DEFINED
+#include "../private/SkOnce.h"
#include "SkTypes.h"
-#include "../private/SkAtomics.h"
-#include "../private/SkOncePtr.h"
+#include <atomic>
-struct SkBaseSemaphore {
+class SkBaseSemaphore {
+public:
+ constexpr SkBaseSemaphore(int count = 0)
+ : fCount(count), fOSSemaphore(nullptr) {}
- // Increment the counter by 1.
- // This is a specialization for supporting SkMutex.
- void signal() {
- // Since this fetches the value before the add, 0 indicates that this thread is running and
- // no threads are waiting, -1 and below means that threads are waiting, but only signal 1
- // thread to run.
- if (sk_atomic_fetch_add(&fCount, 1, sk_memory_order_release) < 0) {
- this->osSignal(1);
- }
- }
-
- // Increment the counter N times.
- // Generally it's better to call signal(N) instead of signal() N times.
- void signal(int N);
+ // Increment the counter n times.
+ // Generally it's better to call signal(n) instead of signal() n times.
+ void signal(int n = 1);
// Decrement the counter by 1,
// then if the counter is <= 0, sleep this thread until the counter is > 0.
- void wait() {
- // Since this fetches the value before the subtract, zero and below means that there are no
- // resources left, so the thread needs to wait.
- if (sk_atomic_fetch_sub(&fCount, 1, sk_memory_order_acquire) <= 0) {
- this->osWait();
- }
- }
+ void wait();
- struct OSSemaphore;
+ // SkBaseSemaphore has no destructor. Call this to clean it up.
+ void cleanup();
- void osSignal(int n);
- void osWait();
- void deleteSemaphore();
-
+private:
// This implementation follows the general strategy of
// 'A Lightweight Semaphore with Partial Spinning'
// found here
@@ -54,33 +38,46 @@
// We wrap an OS-provided semaphore with a user-space atomic counter that
// lets us avoid interacting with the OS semaphore unless strictly required:
// moving the count from >0 to <=0 or vice-versa, i.e. sleeping or waking threads.
- int fCount;
- SkBaseOncePtr<OSSemaphore> fOSSemaphore;
+ struct OSSemaphore;
+
+ void osSignal(int n);
+ void osWait();
+
+ std::atomic<int> fCount;
+ SkOnce fOSSemaphoreOnce;
+ OSSemaphore* fOSSemaphore;
};
-/**
- * SkSemaphore is a fast mostly-user-space semaphore.
- *
- * A semaphore is logically an atomic integer with a few special properties:
- * - The integer always starts at 0.
- * - You can only increment or decrement it, never read or write it.
- * - Increment is spelled 'signal()'; decrement is spelled 'wait()'.
- * - If a call to wait() decrements the counter to <= 0,
- * the calling thread sleeps until another thread signal()s it back above 0.
- */
-class SkSemaphore : SkNoncopyable {
+class SkSemaphore : public SkBaseSemaphore {
public:
- // Initializes the counter to 0.
- // (Though all current implementations could start from an arbitrary value.)
- SkSemaphore();
- ~SkSemaphore();
-
- void wait();
-
- void signal(int n = 1);
-
-private:
- SkBaseSemaphore fBaseSemaphore;
+ using SkBaseSemaphore::SkBaseSemaphore;
+ ~SkSemaphore() { this->cleanup(); }
};
+inline void SkBaseSemaphore::signal(int n) {
+ int prev = fCount.fetch_add(n, std::memory_order_release);
+
+ // We only want to call the OS semaphore when our logical count crosses
+ // from <= 0 to >0 (when we need to wake sleeping threads).
+ //
+ // This is easiest to think about with specific examples of prev and n.
+ // If n == 5 and prev == -3, there are 3 threads sleeping and we signal
+ // SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2.
+ //
+ // If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0,
+ // so we don't call the OS semaphore, leaving the count at (prev + n).
+ int toSignal = SkTMin(-prev, n);
+ if (toSignal > 0) {
+ this->osSignal(toSignal);
+ }
+}
+
+inline void SkBaseSemaphore::wait() {
+ // Since this fetches the value before the subtract, zero and below means that there are no
+ // resources left, so the thread needs to wait.
+ if (fCount.fetch_sub(1, std::memory_order_acquire) <= 0) {
+ this->osWait();
+ }
+}
+
#endif//SkSemaphore_DEFINED
diff --git a/src/core/SkSemaphore.cpp b/src/core/SkSemaphore.cpp
index da422e2..2286c0b 100644
--- a/src/core/SkSemaphore.cpp
+++ b/src/core/SkSemaphore.cpp
@@ -57,43 +57,16 @@
///////////////////////////////////////////////////////////////////////////////
-void SkBaseSemaphore::signal(int n) {
- SkASSERT(n >= 0);
-
- // We only want to call the OS semaphore when our logical count crosses
- // from <= 0 to >0 (when we need to wake sleeping threads).
- //
- // This is easiest to think about with specific examples of prev and n.
- // If n == 5 and prev == -3, there are 3 threads sleeping and we signal
- // SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2.
- //
- // If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0,
- // so we don't call the OS semaphore, leaving the count at (prev + n).
- int prev = sk_atomic_fetch_add(&fCount, n, sk_memory_order_release);
- int toSignal = SkTMin(-prev, n);
- if (toSignal > 0) {
- this->osSignal(toSignal);
- }
+void SkBaseSemaphore::osSignal(int n) {
+ fOSSemaphoreOnce([this] { fOSSemaphore = new OSSemaphore; });
+ fOSSemaphore->signal(n);
}
-static SkBaseSemaphore::OSSemaphore* semaphore(SkBaseSemaphore* semaphore) {
- return semaphore->fOSSemaphore.get([](){ return new SkBaseSemaphore::OSSemaphore(); });
+void SkBaseSemaphore::osWait() {
+ fOSSemaphoreOnce([this] { fOSSemaphore = new OSSemaphore; });
+ fOSSemaphore->wait();
}
-void SkBaseSemaphore::osSignal(int n) { semaphore(this)->signal(n); }
-
-void SkBaseSemaphore::osWait() { semaphore(this)->wait(); }
-
-void SkBaseSemaphore::deleteSemaphore() {
- delete (OSSemaphore*) fOSSemaphore;
+void SkBaseSemaphore::cleanup() {
+ delete fOSSemaphore;
}
-
-///////////////////////////////////////////////////////////////////////////////
-
-SkSemaphore::SkSemaphore(){ fBaseSemaphore = {0, {0}}; }
-
-SkSemaphore::~SkSemaphore() { fBaseSemaphore.deleteSemaphore(); }
-
-void SkSemaphore::wait() { fBaseSemaphore.wait(); }
-
-void SkSemaphore::signal(int n) {fBaseSemaphore.signal(n); }