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/*
* Copyright 2017 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#include "SkExecutor.h"
#include "SkMakeUnique.h"
#include "SkMutex.h"
#include "SkSemaphore.h"
#include "SkSpinlock.h"
#include "SkTArray.h"
#include <deque>
#include <thread>
#if defined(SK_BUILD_FOR_WIN)
#include "SkLeanWindows.h"
static int num_cores() {
SYSTEM_INFO sysinfo;
GetNativeSystemInfo(&sysinfo);
return (int)sysinfo.dwNumberOfProcessors;
}
#else
#include <unistd.h>
static int num_cores() {
return (int)sysconf(_SC_NPROCESSORS_ONLN);
}
#endif
SkExecutor::~SkExecutor() {}
// The default default SkExecutor is an SkTrivialExecutor, which just runs the work right away.
class SkTrivialExecutor final : public SkExecutor {
void add(std::function<void(void)> work) override {
work();
}
};
static SkTrivialExecutor gTrivial;
static SkExecutor* gDefaultExecutor = &gTrivial;
SkExecutor& SkExecutor::GetDefault() {
return *gDefaultExecutor;
}
void SkExecutor::SetDefault(SkExecutor* executor) {
gDefaultExecutor = executor ? executor : &gTrivial;
}
// We'll always push_back() new work, but pop from the front of deques or the back of SkTArray.
static inline std::function<void(void)> pop(std::deque<std::function<void(void)>>* list) {
std::function<void(void)> fn = std::move(list->front());
list->pop_front();
return fn;
}
static inline std::function<void(void)> pop(SkTArray<std::function<void(void)>>* list) {
std::function<void(void)> fn = std::move(list->back());
list->pop_back();
return fn;
}
// An SkThreadPool is an executor that runs work on a fixed pool of OS threads.
template <typename WorkList>
class SkThreadPool final : public SkExecutor {
public:
explicit SkThreadPool(int threads) {
for (int i = 0; i < threads; i++) {
fThreads.emplace_back(&Loop, this);
}
}
~SkThreadPool() override {
// Signal each thread that it's time to shut down.
for (int i = 0; i < fThreads.count(); i++) {
this->add(nullptr);
}
// Wait for each thread to shut down.
for (int i = 0; i < fThreads.count(); i++) {
fThreads[i].join();
}
}
virtual void add(std::function<void(void)> work) override {
// Add some work to our pile of work to do.
{
SkAutoExclusive lock(fWorkLock);
fWork.emplace_back(std::move(work));
}
// Tell the Loop() threads to pick it up.
fWorkAvailable.signal(1);
}
virtual void borrow() override {
// If there is work waiting, do it.
if (fWorkAvailable.try_wait()) {
SkAssertResult(this->do_work());
}
}
private:
// This method should be called only when fWorkAvailable indicates there's work to do.
bool do_work() {
std::function<void(void)> work;
{
SkAutoExclusive lock(fWorkLock);
SkASSERT(!fWork.empty()); // TODO: if (fWork.empty()) { return true; } ?
work = pop(&fWork);
}
if (!work) {
return false; // This is Loop()'s signal to shut down.
}
work();
return true;
}
static void Loop(void* ctx) {
auto pool = (SkThreadPool*)ctx;
do {
pool->fWorkAvailable.wait();
} while (pool->do_work());
}
// Both SkMutex and SkSpinlock can work here.
using Lock = SkMutex;
SkTArray<std::thread> fThreads;
WorkList fWork;
Lock fWorkLock;
SkSemaphore fWorkAvailable;
};
std::unique_ptr<SkExecutor> SkExecutor::MakeFIFOThreadPool(int threads) {
using WorkList = std::deque<std::function<void(void)>>;
return skstd::make_unique<SkThreadPool<WorkList>>(threads > 0 ? threads : num_cores());
}
std::unique_ptr<SkExecutor> SkExecutor::MakeLIFOThreadPool(int threads) {
using WorkList = SkTArray<std::function<void(void)>>;
return skstd::make_unique<SkThreadPool<WorkList>>(threads > 0 ? threads : num_cores());
}
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