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#include "SkTaskGroup.h"
#include "SkCondVar.h"
#include "SkLazyPtr.h"
#include "SkTDArray.h"
#include "SkThread.h"
#include "SkThreadUtils.h"
#if defined(SK_BUILD_FOR_WIN32)
static inline int num_cores() {
SYSTEM_INFO sysinfo;
GetSystemInfo(&sysinfo);
return sysinfo.dwNumberOfProcessors;
}
#else
#include <unistd.h>
static inline int num_cores() {
return (int) sysconf(_SC_NPROCESSORS_ONLN);
}
#endif
namespace {
static int gThreadCount = 0;
class ThreadPool : SkNoncopyable {
public:
static void Add(SkRunnable* task, int32_t* pending) {
Global()->add(task, pending);
}
static void Wait(int32_t* pending) {
while (sk_acquire_load(pending) > 0) { // Pairs with sk_atomic_dec here or in Loop.
// Lend a hand until our SkTaskGroup of interest is done.
ThreadPool* pool = Global();
Work work;
{
AutoLock lock(&pool->fReady);
if (pool->fWork.isEmpty()) {
// Someone has picked up all the work (including ours). How nice of them!
// (They may still be working on it, so we can't assert *pending == 0 here.)
continue;
}
pool->fWork.pop(&work);
}
// This Work isn't necessarily part of our SkTaskGroup of interest, but that's fine.
// We threads gotta stick together. We're always making forward progress.
work.task->run();
sk_atomic_dec(work.pending); // Release pairs with the sk_acquire_load() just above.
}
}
private:
struct AutoLock {
AutoLock(SkCondVar* c) : fC(c) { fC->lock(); }
~AutoLock() { fC->unlock(); }
private:
SkCondVar* fC;
};
struct Work {
SkRunnable* task; // A task to ->run(),
int32_t* pending; // then sk_atomic_dec(pending) afterwards.
};
static ThreadPool* Create() { return SkNEW(ThreadPool); }
static void Destroy(ThreadPool* p) { SkDELETE(p); }
static ThreadPool* Global() {
SK_DECLARE_STATIC_LAZY_PTR(ThreadPool, global, Create, Destroy);
return global.get();
}
ThreadPool() : fDraining(false) {
const int threads = gThreadCount ? gThreadCount : num_cores();
for (int i = 0; i < threads; i++) {
fThreads.push(SkNEW_ARGS(SkThread, (&ThreadPool::Loop, this)));
fThreads.top()->start();
}
}
~ThreadPool() {
SkASSERT(fWork.isEmpty()); // All SkTaskGroups should be destroyed by now.
{
AutoLock lock(&fReady);
fDraining = true;
fReady.broadcast();
}
for (int i = 0; i < fThreads.count(); i++) {
fThreads[i]->join();
}
SkASSERT(fWork.isEmpty()); // Can't hurt to double check.
fThreads.deleteAll();
}
void add(SkRunnable* task, int32_t* pending) {
Work work = { task, pending };
sk_atomic_inc(pending); // No barrier needed.
{
AutoLock lock(&fReady);
fWork.push(work);
fReady.signal();
}
}
static void Loop(void* arg) {
ThreadPool* pool = (ThreadPool*)arg;
Work work;
while (true) {
{
AutoLock lock(&pool->fReady);
while (pool->fWork.isEmpty()) {
if (pool->fDraining) {
return;
}
pool->fReady.wait();
}
pool->fWork.pop(&work);
}
work.task->run();
sk_atomic_dec(work.pending); // Release pairs with sk_acquire_load() in Wait().
}
}
SkTDArray<Work> fWork;
SkTDArray<SkThread*> fThreads;
SkCondVar fReady;
bool fDraining;
};
} // namespace
void SkTaskGroup::SetThreadCount(int n) { gThreadCount = n; }
SkTaskGroup::SkTaskGroup() : fPending(0) {}
void SkTaskGroup::add(SkRunnable* task) { ThreadPool::Add(task, &fPending); }
void SkTaskGroup::wait() { ThreadPool::Wait(&fPending); }
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