Current File : //proc/self/root/backups/router/usr/local/include/kea/asiolink/io_service_thread_pool.h
// Copyright (C) 2022-2024 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef IOSERVICE_THREAD_POOL_H
#define IOSERVICE_THREAD_POOL_H
#include <asiolink/io_service.h>
#include <util/unlock_guard.h>
#include <boost/shared_ptr.hpp>
#include <condition_variable>
#include <list>
#include <mutex>
#include <thread>
namespace isc {
namespace asiolink {
/// @brief Implements a pausable pool of IOService driven threads.
class IoServiceThreadPool {
public:
/// @brief Describes the possible operational state of the thread pool.
enum class State {
STOPPED, /// Pool is not operational.
RUNNING, /// Pool is populated with running threads.
PAUSED, /// Pool is populated with threads that are paused.
};
/// @brief Constructor
///
/// @param io_service IOService that will drive the pool's IO. If empty, it
/// create its own instance.
/// @param pool_size Maximum number of threads in the pool. Currently the
/// number of threads is fixed at this value.
/// @param defer_start If true, creation of the threads is deferred until
/// a subsequent call to @ref run(). In this case the pool's operational
/// state post construction is STOPPED. If false, the constructor will
/// invoke run() to transition the pool into the RUNNING state.
IoServiceThreadPool(asiolink::IOServicePtr io_service, size_t pool_size,
bool defer_start = false);
/// @brief Destructor
///
/// Ensures the thread pool is stopped prior to destruction.
~IoServiceThreadPool();
/// @brief Transitions the pool from STOPPED or PAUSED to RUNNING.
///
/// When called from the STOPPED state, the pool threads are created and
/// begin processing events.
/// When called from the PAUSED state, the pool threads are released
/// from PAUSED and resume processing events.
/// Has no effect if the pool is already in the RUNNING state.
void run();
/// @brief Transitions the pool from RUNNING to PAUSED.
///
/// Pool threads suspend event processing and pause until they
/// are released to either resume running or stop.
/// Has no effect if the pool is already in the PAUSED or STOPPED
/// state.
void pause();
/// @brief Transitions the pool from RUNNING or PAUSED to STOPPED.
///
/// Stops thread event processing and then destroys the pool's threads
/// Has no effect if the pool is already in the STOPPED state.
void stop();
/// @brief Check if the thread pool is running.
///
/// @return True if the thread pool is running, false otherwise.
bool isRunning() {
return (getState() == State::RUNNING);
}
/// @brief Check if the thread pool is paused.
///
/// @return True if the thread pool is paused, false otherwise.
bool isPaused() {
return (getState() == State::PAUSED);
}
/// @brief Check if the thread pool is stopped.
///
/// @return True if the thread pool is stopped, false otherwise.
bool isStopped() {
return (getState() == State::STOPPED);
}
/// @brief Check current thread permissions to transition to the new PAUSED
/// state.
///
/// This function throws @ref MultiThreadingInvalidOperation if the calling
/// thread is one of the worker threads. This would prevent a dead-lock if
/// the calling thread would try to perform a thread pool state transition
/// to PAUSED state.
///
/// @throw MultiThreadingInvalidOperation if the state transition is done on
/// any of the worker threads.
void checkPausePermissions();
private:
/// @brief Check current thread permissions to transition to the new state.
///
/// This function throws @ref MultiThreadingInvalidOperation if the calling
/// thread is one of the worker threads. This would prevent a dead-lock if
/// the calling thread would try to perform a thread pool state transition.
///
/// @param state The new transition state for the pool.
/// @throw MultiThreadingInvalidOperation if the state transition is done on
/// any of the worker threads.
void checkPermissions(State state);
/// @brief Check specified thread id against own threads.
///
/// @return true if thread is owned, false otherwise.
bool checkThreadId(std::thread::id id);
/// @brief Thread-safe change of the pool's run state.
///
/// Transitions a pool from one run state to another:
///
/// When moving from STOPPED or PAUSED to RUNNING:
/// -# Sets state to RUNNING.
/// -# Notifies threads of state change.
/// -# Restarts the IOService.
/// -# Creates the threads if they do not yet exist (true only
/// when transitioning from STOPPED).
/// -# Waits until all threads are running.
/// -# Sets the count of exited threads to 0.
/// -# Returns to caller.
///
/// When moving from RUNNING or PAUSED to STOPPED:
/// -# Sets state to STOPPED
/// -# Notifies threads of state change.
/// -# Polls the IOService to flush handlers.
/// -# Stops the IOService.
/// -# Waits until all threads have exited the work function.
/// -# Joins and destroys the threads.
/// -# Returns to caller.
///
/// When moving from RUNNING to PAUSED:
/// -# Sets state to PAUSED
/// -# Notifies threads of state change.
/// -# Polls the IOService to flush handlers.
/// -# Stops the IOService.
/// -# Waits until all threads have paused.
/// -# Returns to caller.
///
/// @param state The new transition state for the pool.
/// @throw MultiThreadingInvalidOperation if the state transition is done on
/// any of the worker threads.
void setState(State state);
/// @brief Thread-safe fetch of the pool's operational state.
///
/// @return Thread pool state.
State getState();
/// @brief Validates whether the pool can change to a given state.
///
/// @param state new state for the pool.
/// @return true if the change is valid, false otherwise.
/// @note Must be called from a thread-safe context.
bool validateStateChange(State state) const;
/// @brief Text representation of a given state.
///
/// @param state The state for the pool.
/// @return The text representation of a given state.
static std::string stateToText(State state);
/// @brief Work function executed by each thread in the pool.
///
/// Implements the run state responsibilities for a given thread.
/// It executes a run loop until the pool is stopped. At the top
/// of each iteration of the loop the pool's run state is checked
/// and when it is:
///
/// RUNNING:
/// -# The count of threads running is incremented.
/// -# If the count has reached the number of threads in pool the
/// main thread is notified.
/// -# IOService::run() is invoked.
/// -# When IOService::run() returns, the count of threads running
/// is decremented.
///
/// PAUSED:
/// -# The count of threads paused is incremented.
/// -# If the count has reached the number of threads in pool the
/// main thread is notified.
/// -# Thread blocks until notified the pool's run state is no
/// longer PAUSED.
/// -# The count of threads paused is decremented.
///
/// STOPPED:
/// -# The run loop is exited.
/// -# The count of threads exited is incremented.
/// -# If the count has reached the number of threads in pool the
/// main thread is notified.
/// -# The function exits.
void threadWork();
public:
/// @brief Fetches the IOService that drives the pool.
///
/// @return the pointer to the IOService.
asiolink::IOServicePtr getIOService() const;
/// @brief Fetches the maximum size of the thread pool.
///
/// @return the maximum size of the thread pool.
uint16_t getPoolSize() const;
/// @brief Fetches the number of threads in the pool.
///
/// @return the number of running threads.
uint16_t getThreadCount() const;
private:
/// @brief Maximum number of threads in the thread pool.
size_t pool_size_;
/// @brief Pointer to private IOService used in multi-threaded mode.
asiolink::IOServicePtr io_service_;
/// @brief Tracks the operational state of the pool.
State run_state_;
/// @brief Mutex to protect the internal state.
std::mutex mutex_;
/// @brief Condition variable used by threads for synchronization.
std::condition_variable thread_cv_;
/// @brief Condition variable used by main thread to wait on threads
/// state transitions.
std::condition_variable main_cv_;
/// @brief Number of threads currently paused.
size_t paused_;
/// @brief Number of threads currently running.
size_t running_;
/// @brief Number of threads that have exited the work function.
size_t exited_;
/// @brief Pool of threads used to service connections in multi-threaded
/// mode.
std::list<boost::shared_ptr<std::thread> > threads_;
};
/// @brief Defines a pointer to a thread pool.
typedef boost::shared_ptr<IoServiceThreadPool> IoServiceThreadPoolPtr;
} // end of namespace isc::asiolink
} // end of namespace isc
#endif
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