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/*
*
* Copyright 2016 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.
*
*/
#ifndef GRPC_INTERNAL_CPP_THREAD_MANAGER_H
#define GRPC_INTERNAL_CPP_THREAD_MANAGER_H
#include <condition_variable>
#include <list>
#include <memory>
#include <mutex>
#include <thread>
#include <grpc++/support/config.h>
namespace grpc {
class ThreadManager {
public:
explicit ThreadManager(int min_pollers, int max_pollers);
virtual ~ThreadManager();
// Initializes and Starts the Rpc Manager threads
void Initialize();
// The return type of PollForWork() function
enum WorkStatus { WORK_FOUND, SHUTDOWN, TIMEOUT };
// "Polls" for new work.
// If the return value is WORK_FOUND:
// - The implementaion of PollForWork() MAY set some opaque identifier to
// (identify the work item found) via the '*tag' parameter
// - The implementaion MUST set the value of 'ok' to 'true' or 'false'. A
// value of 'false' indicates some implemenation specific error (that is
// neither SHUTDOWN nor TIMEOUT)
// - ThreadManager does not interpret the values of 'tag' and 'ok'
// - ThreadManager WILL call DoWork() and pass '*tag' and 'ok' as input to
// DoWork()
//
// If the return value is SHUTDOWN:,
// - ThreadManager WILL NOT call DoWork() and terminates the thead
//
// If the return value is TIMEOUT:,
// - ThreadManager WILL NOT call DoWork()
// - ThreadManager MAY terminate the thread depending on the current number
// of active poller threads and mix_pollers/max_pollers settings
// - Also, the value of timeout is specific to the derived class
// implementation
virtual WorkStatus PollForWork(void** tag, bool* ok) = 0;
// The implementation of DoWork() is supposed to perform the work found by
// PollForWork(). The tag and ok parameters are the same as returned by
// PollForWork()
//
// The implementation of DoWork() should also do any setup needed to ensure
// that the next call to PollForWork() (not necessarily by the current thread)
// actually finds some work
virtual void DoWork(void* tag, bool ok) = 0;
// Mark the ThreadManager as shutdown and begin draining the work. This is a
// non-blocking call and the caller should call Wait(), a blocking call which
// returns only once the shutdown is complete
virtual void Shutdown();
// Has Shutdown() been called
bool IsShutdown();
// A blocking call that returns only after the ThreadManager has shutdown and
// all the threads have drained all the outstanding work
virtual void Wait();
private:
// Helper wrapper class around std::thread. This takes a ThreadManager object
// and starts a new std::thread to calls the Run() function.
//
// The Run() function calls ThreadManager::MainWorkLoop() function and once
// that completes, it marks the WorkerThread completed by calling
// ThreadManager::MarkAsCompleted()
class WorkerThread {
public:
WorkerThread(ThreadManager* thd_mgr);
~WorkerThread();
private:
// Calls thd_mgr_->MainWorkLoop() and once that completes, calls
// thd_mgr_>MarkAsCompleted(this) to mark the thread as completed
void Run();
ThreadManager* thd_mgr_;
std::thread thd_;
};
// The main funtion in ThreadManager
void MainWorkLoop();
void MarkAsCompleted(WorkerThread* thd);
void CleanupCompletedThreads();
// Protects shutdown_, num_pollers_ and num_threads_
// TODO: sreek - Change num_pollers and num_threads_ to atomics
std::mutex mu_;
bool shutdown_;
std::condition_variable shutdown_cv_;
// Number of threads doing polling
int num_pollers_;
// The minimum and maximum number of threads that should be doing polling
int min_pollers_;
int max_pollers_;
// The total number of threads (includes threads includes the threads that are
// currently polling i.e num_pollers_)
int num_threads_;
std::mutex list_mu_;
std::list<WorkerThread*> completed_threads_;
};
} // namespace grpc
#endif // GRPC_INTERNAL_CPP_THREAD_MANAGER_H
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