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/*
* 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 "../private/SkSemaphore.h"
#if defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_IOS)
#include <mach/mach.h>
struct SkBaseSemaphore::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 SkBaseSemaphore::OSSemaphore {
HANDLE fSemaphore;
OSSemaphore() {
fSemaphore = CreateSemaphore(nullptr /*security attributes, optional*/,
0 /*initial count*/,
MAXLONG /*max count*/,
nullptr /*name, optional*/);
}
~OSSemaphore() { CloseHandle(fSemaphore); }
void signal(int n) {
ReleaseSemaphore(fSemaphore, n, nullptr/*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 SkBaseSemaphore::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
///////////////////////////////////////////////////////////////////////////////
void SkBaseSemaphore::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 = sk_atomic_fetch_add(&fCount, n, sk_memory_order_release);
int toSignal = SkTMin(-prev, n);
if (toSignal > 0) {
this->osSignal(toSignal);
}
}
static SkBaseSemaphore::OSSemaphore* semaphore(SkBaseSemaphore* semaphore) {
return semaphore->fOSSemaphore.get([](){ return new SkBaseSemaphore::OSSemaphore(); });
}
void SkBaseSemaphore::osSignal(int n) { semaphore(this)->signal(n); }
void SkBaseSemaphore::osWait() { semaphore(this)->wait(); }
void SkBaseSemaphore::deleteSemaphore() {
delete (OSSemaphore*) fOSSemaphore;
}
///////////////////////////////////////////////////////////////////////////////
SkSemaphore::SkSemaphore(){ fBaseSemaphore = {0, {0}}; }
SkSemaphore::~SkSemaphore() { fBaseSemaphore.deleteSemaphore(); }
void SkSemaphore::wait() { fBaseSemaphore.wait(); }
void SkSemaphore::signal(int n) {fBaseSemaphore.signal(n); }
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