測(cè)試代碼thread.cpp

#include <thread> #include <iostream> using namespace std;void run(int n){for(int i = 0; i < 5; i++) {cout << "thread " << n << endl;} } int main() {cout << "hahahha" << endl;thread t1(run, 1);thread t2(run, 2);t1.join();t2.join();return 0; }

直接g++編譯一下
g++ thread.cpp -o mythread
會(huì)發(fā)現(xiàn)報(bào)錯(cuò)

In file included from /usr/include/c++/5/thread:35:0,from thread.cpp:1: /usr/include/c++/5/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support must be enabled with the -std=c++11 or -std=gnu++11 compiler options.#error This file requires compiler and library support \

解決方法是g++參數(shù)添加“-std=c++11”，但接著編譯時(shí)，又會(huì)報(bào)另一個(gè)問(wèn)題

$ g++ thread.cpp -std=c++11 -o mythread /tmp/ccbLvKA8.o: In function `std::thread::thread<void (&)(int), int>(void (&)(int), int&&)': thread.cpp:(.text._ZNSt6threadC2IRFviEJiEEEOT_DpOT0_[_ZNSt6threadC5IRFviEJiEEEOT_DpOT0_]+0x93): undefined reference to `pthread_create' collect2: error: ld returned 1 exit status

解決辦法是編譯參數(shù)添加“-lpthread”

$ g++ thread.cpp -std=c++11 -o mythread -lpthead /usr/bin/ld: cannot find -lpthead collect2: error: ld returned 1 exit status $ g++ thread.cpp -std=c++11 -o mythread -lpthread $ ./mythread hahahha thread1 thread1 threadthread2 thread2 thread2 thread2 thread2 1 thread1 thread1

因?yàn)閏out打印不是原子操作，會(huì)導(dǎo)致thread1和thread2混著打印
先試著使用mutex加鎖，更改一下代碼

#include <thread> #include <iostream> #include <mutex>using namespace std;mutex mLock;void run(int n){for(int i = 0; i < 5; i++) {mLock.lock();cout << "thread" << n << endl;mLock.unlock();} }int main() {cout << "hahahha" << endl;thread t1(run, 1);thread t2(run, 2);t1.join();t2.join();return 0; }

運(yùn)行結(jié)果：
$ ./mythread
hahahha
thread1
thread1
thread1
thread1
thread1
thread2
thread2
thread2
thread2
thread2

因?yàn)樵趓un函數(shù)中有可能會(huì)發(fā)現(xiàn)異常，導(dǎo)致unlock沒(méi)有執(zhí)行到，進(jìn)程可能會(huì)掛死
解決辦法是使用lock_guard，由lock_guard控制構(gòu)造和析構(gòu)流程，會(huì)自動(dòng)unlock，運(yùn)行結(jié)果是一樣的。

void run(int n){for(int i = 0; i < 5; i++) {//mLock.lock();lock_guard <mutex> guard(mLock);cout << "thread" << n << endl;//mLock.unlock();} }

也可以利用unique_lock，這個(gè)功能和lock_guard類(lèi)似，但提供的功能更多些，try_to_lock嘗試去lock，可通過(guò)owns_lock判斷是否持鎖成功

void run(int n){for(int i = 0; i < 5; i++) {//mLock.lock();//lock_guard <mutex> guard(mLock);unique_lock <mutex> lock(mLock, try_to_lock);//try to lockcout << "thread" << n << ", lock result:" << lock.owns_lock() << endl;//mLock.unlock();} }

運(yùn)行結(jié)果，偶爾能看到?jīng)]有持到鎖的情況。
$ ./mythread
hahahha
thread1, lock result:1
thread1, lock result:1
thread1, lock result:1
thread1, lock result:1
thread1, lock result:1
thread2, lock result:0
thread2, lock result:1
thread2, lock result:1
thread2, lock result:1
thread2, lock result:1

總結(jié)

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