| /* |
| * Copyright 2015 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #include "SkSemaphore.h" |
| |
| #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS) |
| #include <mach/mach.h> |
| struct SkSemaphore::OSSemaphore { |
| semaphore_t fSemaphore; |
| |
| OSSemaphore() { |
| semaphore_create(mach_task_self(), &fSemaphore, SYNC_POLICY_LIFO, 0/*initial count*/); |
| } |
| ~OSSemaphore() { semaphore_destroy(mach_task_self(), fSemaphore); } |
| |
| void signal(int n) { while (n --> 0) { semaphore_signal(fSemaphore); } } |
| void wait() { semaphore_wait(fSemaphore); } |
| }; |
| #elif defined(SK_BUILD_FOR_WIN32) |
| struct SkSemaphore::OSSemaphore { |
| HANDLE fSemaphore; |
| |
| OSSemaphore() { |
| fSemaphore = CreateSemaphore(NULL /*security attributes, optional*/, |
| 0 /*initial count*/, |
| MAXLONG /*max count*/, |
| NULL /*name, optional*/); |
| } |
| ~OSSemaphore() { CloseHandle(fSemaphore); } |
| |
| void signal(int n) { |
| ReleaseSemaphore(fSemaphore, n, NULL/*returns previous count, optional*/); |
| } |
| void wait() { WaitForSingleObject(fSemaphore, INFINITE/*timeout in ms*/); } |
| }; |
| #else |
| // It's important we test for Mach before this. This code will compile but not work there. |
| #include <errno.h> |
| #include <semaphore.h> |
| struct SkSemaphore::OSSemaphore { |
| sem_t fSemaphore; |
| |
| OSSemaphore() { sem_init(&fSemaphore, 0/*cross process?*/, 0/*initial count*/); } |
| ~OSSemaphore() { sem_destroy(&fSemaphore); } |
| |
| void signal(int n) { while (n --> 0) { sem_post(&fSemaphore); } } |
| void wait() { |
| // Try until we're not interrupted. |
| while(sem_wait(&fSemaphore) == -1 && errno == EINTR); |
| } |
| }; |
| #endif |
| |
| SkSemaphore::SkSemaphore() : fCount(0), fOSSemaphore(SkNEW(OSSemaphore)) {} |
| SkSemaphore::~SkSemaphore() { SkDELETE(fOSSemaphore); } |
| |
| void SkSemaphore::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 = fCount.fetch_add(n, sk_memory_order_release); |
| int toSignal = SkTMin(-prev, n); |
| if (toSignal > 0) { |
| fOSSemaphore->signal(toSignal); |
| } |
| } |
| |
| void SkSemaphore::wait() { |
| // We only wait() on the OS semaphore if the count drops <= 0, |
| // i.e. when we need to make this thread sleep to wait for it to go back up. |
| if (fCount.fetch_add(-1, sk_memory_order_acquire) <= 0) { |
| fOSSemaphore->wait(); |
| } |
| } |