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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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