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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 <grpcpp/support/config.h>
#include "src/core/lib/gprpp/thd.h"
#include "src/core/lib/iomgr/resource_quota.h"
namespace grpc {
class ThreadManager {
public:
explicit ThreadManager(const char* name, grpc_resource_quota* resource_quota,
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 resources parameter indicates that the call actually
// has the resources available for performing the RPC's work. If it doesn't,
// the implementation should fail it appropriately.
//
// 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, bool resources) = 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();
// Max number of concurrent threads that were ever active in this thread
// manager so far. This is useful for debugging purposes (and in unit tests)
// to check if resource_quota is properly being enforced.
int GetMaxActiveThreadsSoFar();
private:
// Helper wrapper class around grpc_core::Thread. Takes a ThreadManager object
// and starts a new grpc_core::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()
//
// WHY IS THIS NEEDED?:
// When a thread terminates, some other thread *must* call Join() on that
// thread so that the resources are released. Having a WorkerThread wrapper
// will make this easier. Once Run() completes, each thread calls the
// following two functions:
// ThreadManager::CleanupCompletedThreads()
// ThreadManager::MarkAsCompleted()
//
// - MarkAsCompleted() puts the WorkerThread object in the ThreadManger's
// completed_threads_ list
// - CleanupCompletedThreads() calls "Join()" on the threads that are already
// in the completed_threads_ list (since a thread cannot call Join() on
// itself, it calls CleanupCompletedThreads() *before* calling
// MarkAsCompleted())
//
// TODO(sreek): Consider creating the threads 'detached' so that Join() need
// not be called (and the need for this WorkerThread class is eliminated)
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* const thd_mgr_;
grpc_core::Thread thd_;
};
// The main funtion in ThreadManager
void MainWorkLoop();
void MarkAsCompleted(WorkerThread* thd);
void CleanupCompletedThreads();
// Protects shutdown_, num_pollers_, num_threads_ and
// max_active_threads_sofar_
std::mutex mu_;
bool shutdown_;
std::condition_variable shutdown_cv_;
// The resource user object to use when requesting quota to create threads
//
// Note: The user of this ThreadManager object must create grpc_resource_quota
// object (that contains the actual max thread quota) and a grpc_resource_user
// object through which quota is requested whenver new threads need to be
// created
grpc_resource_user* resource_user_;
// 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 currently active (includes threads includes the
// threads that are currently polling i.e num_pollers_)
int num_threads_;
// See GetMaxActiveThreadsSoFar()'s description.
// To be more specific, this variable tracks the max value num_threads_ was
// ever set so far
int max_active_threads_sofar_;
std::mutex list_mu_;
std::list<WorkerThread*> completed_threads_;
};
} // namespace grpc
#endif // GRPC_INTERNAL_CPP_THREAD_MANAGER_H
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