1 /* 2 * Copyright 2015 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8 #include "../private/SkSemaphore.h" 9 10 #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS) 11 #include <mach/mach.h> 12 struct SkBaseSemaphore::OSSemaphore { 13 semaphore_t fSemaphore; 14 15 OSSemaphore() { 16 semaphore_create(mach_task_self(), &fSemaphore, SYNC_POLICY_LIFO, 0/*initial count*/); 17 } 18 ~OSSemaphore() { semaphore_destroy(mach_task_self(), fSemaphore); } 19 20 void signal(int n) { while (n --> 0) { semaphore_signal(fSemaphore); } } 21 void wait() { semaphore_wait(fSemaphore); } 22 }; 23 #elif defined(SK_BUILD_FOR_WIN32) 24 struct SkBaseSemaphore::OSSemaphore { 25 HANDLE fSemaphore; 26 27 OSSemaphore() { 28 fSemaphore = CreateSemaphore(nullptr /*security attributes, optional*/, 29 0 /*initial count*/, 30 MAXLONG /*max count*/, 31 nullptr /*name, optional*/); 32 } 33 ~OSSemaphore() { CloseHandle(fSemaphore); } 34 35 void signal(int n) { 36 ReleaseSemaphore(fSemaphore, n, nullptr/*returns previous count, optional*/); 37 } 38 void wait() { WaitForSingleObject(fSemaphore, INFINITE/*timeout in ms*/); } 39 }; 40 #else 41 // It's important we test for Mach before this. This code will compile but not work there. 42 #include <errno.h> 43 #include <semaphore.h> 44 struct SkBaseSemaphore::OSSemaphore { 45 sem_t fSemaphore; 46 47 OSSemaphore() { sem_init(&fSemaphore, 0/*cross process?*/, 0/*initial count*/); } 48 ~OSSemaphore() { sem_destroy(&fSemaphore); } 49 50 void signal(int n) { while (n --> 0) { sem_post(&fSemaphore); } } 51 void wait() { 52 // Try until we're not interrupted. 53 while(sem_wait(&fSemaphore) == -1 && errno == EINTR); 54 } 55 }; 56 #endif 57 58 /////////////////////////////////////////////////////////////////////////////// 59 60 void SkBaseSemaphore::signal(int n) { 61 SkASSERT(n >= 0); 62 63 // We only want to call the OS semaphore when our logical count crosses 64 // from <= 0 to >0 (when we need to wake sleeping threads). 65 // 66 // This is easiest to think about with specific examples of prev and n. 67 // If n == 5 and prev == -3, there are 3 threads sleeping and we signal 68 // SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2. 69 // 70 // If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0, 71 // so we don't call the OS semaphore, leaving the count at (prev + n). 72 int prev = sk_atomic_fetch_add(&fCount, n, sk_memory_order_release); 73 int toSignal = SkTMin(-prev, n); 74 if (toSignal > 0) { 75 this->osSignal(toSignal); 76 } 77 } 78 79 static SkBaseSemaphore::OSSemaphore* semaphore(SkBaseSemaphore* semaphore) { 80 return semaphore->fOSSemaphore.get([](){ return new SkBaseSemaphore::OSSemaphore(); }); 81 } 82 83 void SkBaseSemaphore::osSignal(int n) { semaphore(this)->signal(n); } 84 85 void SkBaseSemaphore::osWait() { semaphore(this)->wait(); } 86 87 void SkBaseSemaphore::deleteSemaphore() { 88 delete (OSSemaphore*) fOSSemaphore; 89 } 90 91 /////////////////////////////////////////////////////////////////////////////// 92 93 SkSemaphore::SkSemaphore(){ fBaseSemaphore = {0, {0}}; } 94 95 SkSemaphore::~SkSemaphore() { fBaseSemaphore.deleteSemaphore(); } 96 97 void SkSemaphore::wait() { fBaseSemaphore.wait(); } 98 99 void SkSemaphore::signal(int n) {fBaseSemaphore.signal(n); } 100
