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| 1 /* | 1 /* |
| 2 * Copyright 2015 Google Inc. | 2 * Copyright 2015 Google Inc. |
| 3 * | 3 * |
| 4 * Use of this source code is governed by a BSD-style license that can be | 4 * Use of this source code is governed by a BSD-style license that can be |
| 5 * found in the LICENSE file. | 5 * found in the LICENSE file. |
| 6 */ | 6 */ |
| 7 | 7 |
| 8 #include "SkSemaphore.h" | 8 #include "SkSemaphore.h" |
| 9 | 9 |
| 10 #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS) | 10 #if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS) |
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| 48 ~OSSemaphore() { sem_destroy(&fSemaphore); } | 48 ~OSSemaphore() { sem_destroy(&fSemaphore); } |
| 49 | 49 |
| 50 void signal(int n) { while (n --> 0) { sem_post(&fSemaphore); } } | 50 void signal(int n) { while (n --> 0) { sem_post(&fSemaphore); } } |
| 51 void wait() { | 51 void wait() { |
| 52 // Try until we're not interrupted. | 52 // Try until we're not interrupted. |
| 53 while(sem_wait(&fSemaphore) == -1 && errno == EINTR); | 53 while(sem_wait(&fSemaphore) == -1 && errno == EINTR); |
| 54 } | 54 } |
| 55 }; | 55 }; |
| 56 #endif | 56 #endif |
| 57 | 57 |
| 58 SkSemaphore::SkSemaphore() : fCount(0), fOSSemaphore(SkNEW(OSSemaphore)) {} | 58 SkSemaphore::SkSemaphore() : fCount(0), fOSSemaphore(new OSSemaphore) {} |
| 59 SkSemaphore::~SkSemaphore() { SkDELETE(fOSSemaphore); } | 59 SkSemaphore::~SkSemaphore() { delete fOSSemaphore; } |
| 60 | 60 |
| 61 void SkSemaphore::signal(int n) { | 61 void SkSemaphore::signal(int n) { |
| 62 SkASSERT(n >= 0); | 62 SkASSERT(n >= 0); |
| 63 | 63 |
| 64 // We only want to call the OS semaphore when our logical count crosses | 64 // We only want to call the OS semaphore when our logical count crosses |
| 65 // from <= 0 to >0 (when we need to wake sleeping threads). | 65 // from <= 0 to >0 (when we need to wake sleeping threads). |
| 66 // | 66 // |
| 67 // This is easiest to think about with specific examples of prev and n. | 67 // This is easiest to think about with specific examples of prev and n. |
| 68 // If n == 5 and prev == -3, there are 3 threads sleeping and we signal | 68 // If n == 5 and prev == -3, there are 3 threads sleeping and we signal |
| 69 // SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2. | 69 // SkTMin(-(-3), 5) == 3 times on the OS semaphore, leaving the count at 2. |
| 70 // | 70 // |
| 71 // If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0, | 71 // If prev >= 0, no threads are waiting, SkTMin(-prev, n) is always <= 0, |
| 72 // so we don't call the OS semaphore, leaving the count at (prev + n). | 72 // so we don't call the OS semaphore, leaving the count at (prev + n). |
| 73 int prev = fCount.fetch_add(n, sk_memory_order_release); | 73 int prev = fCount.fetch_add(n, sk_memory_order_release); |
| 74 int toSignal = SkTMin(-prev, n); | 74 int toSignal = SkTMin(-prev, n); |
| 75 if (toSignal > 0) { | 75 if (toSignal > 0) { |
| 76 fOSSemaphore->signal(toSignal); | 76 fOSSemaphore->signal(toSignal); |
| 77 } | 77 } |
| 78 } | 78 } |
| 79 | 79 |
| 80 void SkSemaphore::wait() { | 80 void SkSemaphore::wait() { |
| 81 // We only wait() on the OS semaphore if the count drops <= 0, | 81 // We only wait() on the OS semaphore if the count drops <= 0, |
| 82 // i.e. when we need to make this thread sleep to wait for it to go back up. | 82 // i.e. when we need to make this thread sleep to wait for it to go back up. |
| 83 if (fCount.fetch_add(-1, sk_memory_order_acquire) <= 0) { | 83 if (fCount.fetch_add(-1, sk_memory_order_acquire) <= 0) { |
| 84 fOSSemaphore->wait(); | 84 fOSSemaphore->wait(); |
| 85 } | 85 } |
| 86 } | 86 } |
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