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/*
*
* Copyright 2015 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
#include "src/cpp/server/dynamic_thread_pool.h"
#include <mutex>
#include <grpc/support/log.h>
#include "src/core/lib/gprpp/thd.h"
namespace grpc {
DynamicThreadPool::DynamicThread::DynamicThread(DynamicThreadPool* pool)
: pool_(pool),
thd_("grpcpp_dynamic_pool",
[](void* th) {
static_cast<DynamicThreadPool::DynamicThread*>(th)->ThreadFunc();
},
this) {
thd_.Start();
}
DynamicThreadPool::DynamicThread::~DynamicThread() { thd_.Join(); }
void DynamicThreadPool::DynamicThread::ThreadFunc() {
pool_->ThreadFunc();
// Now that we have killed ourselves, we should reduce the thread count
std::unique_lock<std::mutex> lock(pool_->mu_);
pool_->nthreads_--;
// Move ourselves to dead list
pool_->dead_threads_.push_back(this);
if ((pool_->shutdown_) && (pool_->nthreads_ == 0)) {
pool_->shutdown_cv_.notify_one();
}
}
void DynamicThreadPool::ThreadFunc() {
for (;;) {
// Wait until work is available or we are shutting down.
std::unique_lock<std::mutex> lock(mu_);
if (!shutdown_ && callbacks_.empty()) {
// If there are too many threads waiting, then quit this thread
if (threads_waiting_ >= reserve_threads_) {
break;
}
threads_waiting_++;
cv_.wait(lock);
threads_waiting_--;
}
// Drain callbacks before considering shutdown to ensure all work
// gets completed.
if (!callbacks_.empty()) {
auto cb = callbacks_.front();
callbacks_.pop();
lock.unlock();
cb();
} else if (shutdown_) {
break;
}
}
}
DynamicThreadPool::DynamicThreadPool(int reserve_threads)
: shutdown_(false),
reserve_threads_(reserve_threads),
nthreads_(0),
threads_waiting_(0) {
for (int i = 0; i < reserve_threads_; i++) {
std::lock_guard<std::mutex> lock(mu_);
nthreads_++;
new DynamicThread(this);
}
}
void DynamicThreadPool::ReapThreads(std::list<DynamicThread*>* tlist) {
for (auto t = tlist->begin(); t != tlist->end(); t = tlist->erase(t)) {
delete *t;
}
}
DynamicThreadPool::~DynamicThreadPool() {
std::unique_lock<std::mutex> lock(mu_);
shutdown_ = true;
cv_.notify_all();
while (nthreads_ != 0) {
shutdown_cv_.wait(lock);
}
ReapThreads(&dead_threads_);
}
void DynamicThreadPool::Add(const std::function<void()>& callback) {
std::lock_guard<std::mutex> lock(mu_);
// Add works to the callbacks list
callbacks_.push(callback);
// Increase pool size or notify as needed
if (threads_waiting_ == 0) {
// Kick off a new thread
nthreads_++;
new DynamicThread(this);
} else {
cv_.notify_one();
}
// Also use this chance to harvest dead threads
if (!dead_threads_.empty()) {
ReapThreads(&dead_threads_);
}
}
} // namespace grpc
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