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
OSSemaphoreSkBaseSemaphore::OSSemaphore15 OSSemaphore() {
16 semaphore_create(mach_task_self(), &fSemaphore, SYNC_POLICY_LIFO, 0/*initial count*/);
17 }
~OSSemaphoreSkBaseSemaphore::OSSemaphore18 ~OSSemaphore() { semaphore_destroy(mach_task_self(), fSemaphore); }
19
signalSkBaseSemaphore::OSSemaphore20 void signal(int n) { while (n --> 0) { semaphore_signal(fSemaphore); } }
waitSkBaseSemaphore::OSSemaphore21 void wait() { semaphore_wait(fSemaphore); }
22 };
23 #elif defined(SK_BUILD_FOR_WIN32)
24 struct SkBaseSemaphore::OSSemaphore {
25 HANDLE fSemaphore;
26
OSSemaphoreSkBaseSemaphore::OSSemaphore27 OSSemaphore() {
28 fSemaphore = CreateSemaphore(nullptr /*security attributes, optional*/,
29 0 /*initial count*/,
30 MAXLONG /*max count*/,
31 nullptr /*name, optional*/);
32 }
~OSSemaphoreSkBaseSemaphore::OSSemaphore33 ~OSSemaphore() { CloseHandle(fSemaphore); }
34
signalSkBaseSemaphore::OSSemaphore35 void signal(int n) {
36 ReleaseSemaphore(fSemaphore, n, nullptr/*returns previous count, optional*/);
37 }
waitSkBaseSemaphore::OSSemaphore38 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
OSSemaphoreSkBaseSemaphore::OSSemaphore47 OSSemaphore() { sem_init(&fSemaphore, 0/*cross process?*/, 0/*initial count*/); }
~OSSemaphoreSkBaseSemaphore::OSSemaphore48 ~OSSemaphore() { sem_destroy(&fSemaphore); }
49
signalSkBaseSemaphore::OSSemaphore50 void signal(int n) { while (n --> 0) { sem_post(&fSemaphore); } }
waitSkBaseSemaphore::OSSemaphore51 void wait() {
52 // Try until we're not interrupted.
53 while(sem_wait(&fSemaphore) == -1 && errno == EINTR);
54 }
55 };
56 #endif
57
58 ///////////////////////////////////////////////////////////////////////////////
59
signal(int n)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
semaphore(SkBaseSemaphore * semaphore)79 static SkBaseSemaphore::OSSemaphore* semaphore(SkBaseSemaphore* semaphore) {
80 return semaphore->fOSSemaphore.get([](){ return new SkBaseSemaphore::OSSemaphore(); });
81 }
82
osSignal(int n)83 void SkBaseSemaphore::osSignal(int n) { semaphore(this)->signal(n); }
84
osWait()85 void SkBaseSemaphore::osWait() { semaphore(this)->wait(); }
86
deleteSemaphore()87 void SkBaseSemaphore::deleteSemaphore() {
88 delete (OSSemaphore*) fOSSemaphore;
89 }
90
91 ///////////////////////////////////////////////////////////////////////////////
92
SkSemaphore()93 SkSemaphore::SkSemaphore(){ fBaseSemaphore = {0, {0}}; }
94
~SkSemaphore()95 SkSemaphore::~SkSemaphore() { fBaseSemaphore.deleteSemaphore(); }
96
wait()97 void SkSemaphore::wait() { fBaseSemaphore.wait(); }
98
signal(int n)99 void SkSemaphore::signal(int n) {fBaseSemaphore.signal(n); }
100