基於C++11實現線程池的工作原理.
目錄
不久前寫過一篇線程池，那時候剛用C++寫東西不久，很多C++標准庫里面的東西沒怎么用，今天基於C++11重新實現了一個線程池。
簡介
線程池（thread pool）：一種線程的使用模式，線程過多會帶來調度開銷，進而影響緩存局部性和整體性能。而線程池維護着多個線程，等待着監督管理者分配可並發執行的任務。這避免了在處理短時間任務時創建與銷毀線程的代價。線程池不僅能夠保證內核的充分利用，還能防止過分調度。可用線程數量應該取決於可用的並發處理器、處理器內核、內存、網絡sockets等的數量。
線程池的組成
1、線程池管理器
創建一定數量的線程，啟動線程，調配任務，管理着線程池。
本篇線程池目前只需要啟動(start())，停止方法(stop())，及任務添加方法(addTask).
start()創建一定數量的線程池,進行線程循環.
stop()停止所有線程循環，回收所有資源.
addTask()添加任務.
2、工作線程
線程池中線程，在線程池中等待並執行分配的任務.
本篇選用條件變量實現等待與通知機制.
3、任務接口，
添加任務的接口,以供工作線程調度任務的執行。
4、任務隊列
用於存放沒有處理的任務。提供一種緩沖機制
同時任務隊列具有調度功能，高優先級的任務放在任務隊列前面;本篇選用priority_queue 與pair的結合用作任務優先隊列的結構.
線程池工作的四種情況.
假設我們的線程池大小為3，任務隊列目前不做大小限制.
1、主程序當前沒有任務要執行，線程池中的任務隊列為空閑狀態.
此情況下所有工作線程處於空閑的等待狀態，任務緩沖隊列為空.
2、主程序添加小於等於線程池中線程數量的任務.
此情況基於情形1，所有工作線程已處在等待狀態，主線程開始添加三個任務，添加后通知(notif())喚醒線程池中的線程開始取(take())任務執行. 此時的任務緩沖隊列還是空。
3、主程序添加任務數量大於當前線程池中線程數量的任務.
此情況發生情形2后面，所有工作線程都在工作中，主線程開始添加第四個任務，添加后發現現在線程池中的線程用完了,於是存入任務緩沖隊列。工作線程空閑后主動從任務隊列取任務執行.
4、主程序添加任務數量大於當前線程池中線程數量的任務,且任務緩沖隊列已滿.
此情況發生情形3且設置了任務緩沖隊列大小后面，主程序添加第N個任務，添加后發現池子中的線程用完了，任務緩沖隊列也滿了，於是進入等待狀態、等待任務緩沖隊列中的任務騰空通知。
但是要注意這種情形會阻塞主線程,本篇暫不限制任務隊列大小,必要時再來優化.
實現
等待通知機制通過條件變量實現，Logger和CurrentThread,用於調試，可以無視.
#ifndef _THREADPOOL_HH
#define _THREADPOOL_HH
#include <vector>
#include <utility>
#include <queue>
#include <thread>
#include <functional>
#include <mutex>
#include "Condition.hh"
class ThreadPool{
public:
static const int kInitThreadsSize = 3;
enum taskPriorityE { level0, level1, level2, };
typedef std::function<void()> Task;
typedef std::pair<taskPriorityE, Task> TaskPair;
ThreadPool();
~ThreadPool();
void start();
void stop();
void addTask(const Task&);
void addTask(const TaskPair&);
private:
ThreadPool(const ThreadPool&);//禁止復制拷貝.
const ThreadPool& operator=(const ThreadPool&);
struct TaskPriorityCmp
{
bool operator()(const ThreadPool::TaskPair p1, const ThreadPool::TaskPair p2)
{
return p1.first > p2.first; //first的小值優先
}
};
void threadLoop();
Task take();
typedef std::vector<std::thread*> Threads;
typedef std::priority_queue<TaskPair, std::vector<TaskPair>, TaskPriorityCmp> Tasks;
Threads m_threads;
Tasks m_tasks;
std::mutex m_mutex;
Condition m_cond;
bool m_isStarted;
};
#endif
//Cpp
#include <assert.h>
#include "Logger.hh" // debug
#include "CurrentThread.hh" // debug
#include "ThreadPool.hh"
ThreadPool::ThreadPool()
:m_mutex(),
m_cond(m_mutex),
m_isStarted(false)
{
}
ThreadPool::~ThreadPool()
{
if(m_isStarted)
{
stop();
}
}
void ThreadPool::start()
{
assert(m_threads.empty());
m_isStarted = true;
m_threads.reserve(kInitThreadsSize);
for (int i = 0; i < kInitThreadsSize; ++i)
{
m_threads.push_back(new std::thread(std::bind(&ThreadPool::threadLoop, this)));
}
}
void ThreadPool::stop()
{
LOG_TRACE << "ThreadPool::stop() stop.";
{
std::unique_lock<std::mutex> lock(m_mutex);
m_isStarted = false;
m_cond.notifyAll();
LOG_TRACE << "ThreadPool::stop() notifyAll().";
}
for (Threads::iterator it = m_threads.begin(); it != m_threads.end() ; ++it)
{
(*it)->join();
delete *it;
}
m_threads.clear();
}
void ThreadPool::threadLoop()
{
LOG_TRACE << "ThreadPool::threadLoop() tid : " << CurrentThread::tid() << " start.";
while(m_isStarted)
{
Task task = take();
if(task)
{
task();
}
}
LOG_TRACE << "ThreadPool::threadLoop() tid : " << CurrentThread::tid() << " exit.";
}
void ThreadPool::addTask(const Task& task)
{
std::unique_lock<std::mutex> lock(m_mutex);
/*while(m_tasks.isFull())
{//when m_tasks have maxsize
cond2.wait();
}
*/
TaskPair taskPair(level2, task);
m_tasks.push(taskPair);
m_cond.notify();
}
void ThreadPool::addTask(const TaskPair& taskPair)
{
std::unique_lock<std::mutex> lock(m_mutex);
/*while(m_tasks.isFull())
{//when m_tasks have maxsize
cond2.wait();
}
*/
m_tasks.push(taskPair);
m_cond.notify();
}
ThreadPool::Task ThreadPool::take()
{
std::unique_lock<std::mutex> lock(m_mutex);
//always use a while-loop, due to spurious wakeup
while(m_tasks.empty() && m_isStarted)
{
LOG_TRACE << "ThreadPool::take() tid : " << CurrentThread::tid() << " wait.";
m_cond.wait(lock);
}
LOG_TRACE << "ThreadPool::take() tid : " << CurrentThread::tid() << " wakeup.";
Task task;
Tasks::size_type size = m_tasks.size();
if(!m_tasks.empty() && m_isStarted)
{
task = m_tasks.top().second;
m_tasks.pop();
assert(size - 1 == m_tasks.size());
/*if (TaskQueueSize_ > 0)
{
cond2.notify();
}*/
}
return task;
}
測試程序
start() 、stop()
測試線程池基本的創建退出工作，及檢測資源是否正常回收.
int main()
{
{
ThreadPool threadPool;
threadPool.start();
getchar();
}
getchar();
return 0;
}
./test.out
2018-11-25 16:50:36.054805 [TRACE] [ThreadPool.cpp:53] [threadLoop] ThreadPool::threadLoop() tid : 3680 start.
2018-11-25 16:50:36.054855 [TRACE] [ThreadPool.cpp:72] [take] ThreadPool::take() tid : 3680 wait.
2018-11-25 16:50:36.055633 [TRACE] [ThreadPool.cpp:53] [threadLoop] ThreadPool::threadLoop() tid : 3679 start.
2018-11-25 16:50:36.055676 [TRACE] [ThreadPool.cpp:72] [take] ThreadPool::take() tid : 3679 wait.
2018-11-25 16:50:36.055641 [TRACE] [ThreadPool.cpp:53] [threadLoop] ThreadPool::threadLoop() tid : 3681 start.
2018-11-25 16:50:36.055701 [TRACE] [ThreadPool.cpp:72] [take] ThreadPool::take() tid : 3681 wait.
2018-11-25 16:50:36.055736 [TRACE] [ThreadPool.cpp:53] [threadLoop] ThreadPool::threadLoop() tid : 3682 start.
2018-11-25 16:50:36.055746 [TRACE] [ThreadPool.cpp:72] [take] ThreadPool::take() tid : 3682 wait.
2018-11-25 16:51:01.411792 [TRACE] [ThreadPool.cpp:36] [stop] ThreadPool::stop() stop.
2018-11-25 16:51:01.411863 [TRACE] [ThreadPool.cpp:39] [stop] ThreadPool::stop() notifyAll().
2018-11-25 16:51:01.411877 [TRACE] [ThreadPool.cpp:76] [take] ThreadPool::take() tid : 3680 wakeup.
2018-11-25 16:51:01.411883 [TRACE] [ThreadPool.cpp:62] [threadLoop] ThreadPool::threadLoop() tid : 3680 exit.
2018-11-25 16:51:01.412062 [TRACE] [ThreadPool.cpp:76] [take] ThreadPool::take() tid : 3682 wakeup.
2018-11-25 16:51:01.412110 [TRACE] [ThreadPool.cpp:62] [threadLoop] ThreadPool::threadLoop() tid : 3682 exit.
2018-11-25 16:51:01.413052 [TRACE] [ThreadPool.cpp:76] [take] ThreadPool::take() tid : 3679 wakeup.
2018-11-25 16:51:01.413098 [TRACE] [ThreadPool.cpp:62] [threadLoop] ThreadPool::threadLoop() tid : 3679 exit.
2018-11-25 16:51:01.413112 [TRACE] [ThreadPool.cpp:76] [take] ThreadPool::take() tid : 3681 wakeup.
2018-11-25 16:51:01.413141 [TRACE] [ThreadPool.cpp:62] [threadLoop] ThreadPool::threadLoop() tid : 3681 exit.
addTask()、PriorityTaskQueue
測試添加任務接口，及優先任務隊列.
主線程首先添加了5個普通任務、 1s后添加一個高優先級任務，當前3個線程中的最先一個空閑后，會最先執行后面添加的priorityFunc().
std::mutex g_mutex;
void priorityFunc()
{
for (int i = 1; i < 4; ++i)
{
std::this_thread::sleep_for(std::chrono::seconds(1));
std::lock_guard<std::mutex> lock(g_mutex);
LOG_DEBUG << "priorityFunc() [" << i << "at thread [ " << CurrentThread::tid() << "] output";// << std::endl;
}
}
void testFunc()
{
// loop to print character after a random period of time
for (int i = 1; i < 4; ++i)
{
std::this_thread::sleep_for(std::chrono::seconds(1));
std::lock_guard<std::mutex> lock(g_mutex);
LOG_DEBUG << "testFunc() [" << i << "] at thread [ " << CurrentThread::tid() << "] output";// << std::endl;
}
}
int main()
{
ThreadPool threadPool;
threadPool.start();
for(int i = 0; i < 5 ; i++)
threadPool.addTask(testFunc);
std::this_thread::sleep_for(std::chrono::seconds(1));
threadPool.addTask(ThreadPool::TaskPair(ThreadPool::level0, priorityFunc));
getchar();
return 0;
}
./test.out
2018-11-25 18:24:20.886837 [TRACE] [ThreadPool.cpp:56] [threadLoop] ThreadPool::threadLoop() tid : 4121 start.
2018-11-25 18:24:20.886893 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4121 wakeup.
2018-11-25 18:24:20.887580 [TRACE] [ThreadPool.cpp:56] [threadLoop] ThreadPool::threadLoop() tid : 4120 start.
2018-11-25 18:24:20.887606 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4120 wakeup.
2018-11-25 18:24:20.887610 [TRACE] [ThreadPool.cpp:56] [threadLoop] ThreadPool::threadLoop() tid : 4122 start.
2018-11-25 18:24:20.887620 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4122 wakeup.
2018-11-25 18:24:21.887779 [DEBUG] [main.cpp:104] [testFunc] testFunc() [1] at thread [ 4120] output
2018-11-25 18:24:21.887813 [DEBUG] [main.cpp:104] [testFunc] testFunc() [1] at thread [ 4122] output
2018-11-25 18:24:21.888909 [DEBUG] [main.cpp:104] [testFunc] testFunc() [1] at thread [ 4121] output
2018-11-25 18:24:22.888049 [DEBUG] [main.cpp:104] [testFunc] testFunc() [2] at thread [ 4120] output
2018-11-25 18:24:22.888288 [DEBUG] [main.cpp:104] [testFunc] testFunc() [2] at thread [ 4122] output
2018-11-25 18:24:22.889978 [DEBUG] [main.cpp:104] [testFunc] testFunc() [2] at thread [ 4121] output
2018-11-25 18:24:23.888467 [DEBUG] [main.cpp:104] [testFunc] testFunc() [3] at thread [ 4120] output
2018-11-25 18:24:23.888724 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4120 wakeup.
2018-11-25 18:24:23.888778 [DEBUG] [main.cpp:104] [testFunc] testFunc() [3] at thread [ 4122] output
2018-11-25 18:24:23.888806 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4122 wakeup.
2018-11-25 18:24:23.890413 [DEBUG] [main.cpp:104] [testFunc] testFunc() [3] at thread [ 4121] output
2018-11-25 18:24:23.890437 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4121 wakeup.
2018-11-25 18:24:24.889247 [DEBUG] [main.cpp:92] [priorityFunc] priorityFunc() [1at thread [ 4120] output
2018-11-25 18:24:24.891187 [DEBUG] [main.cpp:104] [testFunc] testFunc() [1] at thread [ 4121] output
2018-11-25 18:24:24.893163 [DEBUG] [main.cpp:104] [testFunc] testFunc() [1] at thread [ 4122] output
2018-11-25 18:24:25.889567 [DEBUG] [main.cpp:92] [priorityFunc] priorityFunc() [2at thread [ 4120] output
2018-11-25 18:24:25.891477 [DEBUG] [main.cpp:104] [testFunc] testFunc() [2] at thread [ 4121] output
2018-11-25 18:24:25.893450 [DEBUG] [main.cpp:104] [testFunc] testFunc() [2] at thread [ 4122] output
2018-11-25 18:24:26.890295 [DEBUG] [main.cpp:92] [priorityFunc] priorityFunc() [3at thread [ 4120] output
2018-11-25 18:24:26.890335 [TRACE] [ThreadPool.cpp:99] [take] ThreadPool::take() tid : 4120 wait.
2018-11-25 18:24:26.892265 [DEBUG] [main.cpp:104] [testFunc] testFunc() [3] at thread [ 4121] output
2018-11-25 18:24:26.892294 [TRACE] [ThreadPool.cpp:99] [take] ThreadPool::take() tid : 4121 wait.
2018-11-25 18:24:26.894274 [DEBUG] [main.cpp:104] [testFunc] testFunc() [3] at thread [ 4122] output
2018-11-25 18:24:26.894299 [TRACE] [ThreadPool.cpp:99] [take] ThreadPool::take() tid : 4122 wait.
2018-11-25 18:24:35.359003 [TRACE] [ThreadPool.cpp:37] [stop] ThreadPool::stop() stop.
2018-11-25 18:24:35.359043 [TRACE] [ThreadPool.cpp:42] [stop] ThreadPool::stop() notifyAll().
2018-11-25 18:24:35.359061 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4120 wakeup.
2018-11-25 18:24:35.359067 [TRACE] [ThreadPool.cpp:65] [threadLoop] ThreadPool::threadLoop() tid : 4120 exit.
2018-11-25 18:24:35.359080 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4122 wakeup.
2018-11-25 18:24:35.359090 [TRACE] [ThreadPool.cpp:65] [threadLoop] ThreadPool::threadLoop() tid : 4122 exit.
2018-11-25 18:24:35.359123 [TRACE] [ThreadPool.cpp:103] [take] ThreadPool::take() tid : 4121 wakeup.
2018-11-25 18:24:35.359130 [TRACE] [ThreadPool.cpp:65] [threadLoop] ThreadPool::threadLoop() tid : 4121 exit.
源碼下載
如果有需要，可以訪問我的GitHub進行下載: https://github.com/BethlyRoseDaisley/ThreadPool
源碼更新 ---2019-3-7
1、去除優先隊列 該用deque
2、去除condition currentthread 源文件
3、文件重命名
4、增加簡易logger