多线程同步的开发

介绍

根据多线程同步原理中介绍的内容可知，多线程开发就是要让多个线程正确的访问临界资源，实现多线程同步。

所以，一般的同步策略最简单的就是：使用互斥体（mutex）来管理临界资源（与临界资源同时定义，生命期相同，作用域相同），互斥体提供P、V操作（获取，获取不到就等待；释放，唤醒等待的线程）。不同的线程使用锁（Guard）来自动调用（构造函数、析构函数）互斥体的P、V操作，从而实现同步。

互斥体（Mutex）

下面以ACE中互斥体的使用来实现：多个人使用打印机的场景

#include <iostream>#include "ace/Log_Msg.h"#include "ace/Mutex.h"#include "ace/Task.h"class Printer{public:Printer(){}void print(int paper_id){this->mutex_.acquire();ACE_DEBUG((LM_DEBUG,"person(%t) is printing paper(%d)\n",paper_id));ACE_OS::sleep(1);this->mutex_.release();}private:ACE_Thread_Mutex mutex_;};class Person : public ACE_Task_Base{public:Person(Printer& printer):printer_(printer){}virtual int svc(void){ACE_DEBUG((LM_DEBUG,ACE_TEXT("Person(%t) is running\n"))); for (int i=0;i<4;++i){this->printer_.print(i);}return 0;}private:Printer& printer_;};int main(int argc, char *argv[]){Printer printer_obj;Person person1(printer_obj);Person person2(printer_obj);person1.activate();person2.activate();person1.wait();person1.wait();return 0;}

锁（守卫、Guard）

Guard类的主要逻辑是：构造函数通过执行互斥体的P操作获取临界资源；析构函数通过执行互斥体的V操作来释放临界资源。在构造函数之后操作临界资源。构造与析构之间的代码段形成临界区（临界区越小越好）。

Guard类的源码片段：

template <class LOCK>class Guard{public://隐式的切自动的获取锁ACE_Guard (LOCK &lock): lock_(&lock){acquire();}//隐式的释放锁~ACE_Guard (void){release();}//显示的获取锁int acquire (void){return owner_ = lock_->acquire();}//显示的释放锁int release (void){if (owner_ == -1){return -1;} else{owner_ = -1;return lock_->release();}}bool locked (void) const {return owner_ != -1;}protected://用子类来存储指针ACE_Guard (LOCK *lock): lock_ (lock), owner_ (0) {}//指向我们正在看守的LOCKLOCK *lock_;//跟踪记录我们是否获取了锁int owner_;};

下面以ACE中的Guard来实现：多个人使用打印机的场景(仅仅改动了打印机打印的同步代码)

#include <iostream>#include "ace/Log_Msg.h"#include "ace/Mutex.h"#include "ace/Task.h"class Printer{public:Printer(){}void print(int paper_id){ACE_Guard<ACE_Thread_Mutex> guard(this->mutex_);//this->mutex_.acquire();ACE_DEBUG((LM_DEBUG,"person(%t) is printing paper(%d)\n",paper_id));ACE_OS::sleep(1);//this->mutex_.release();}private:ACE_Thread_Mutex mutex_;};class Person : public ACE_Task_Base{public:Person(Printer& printer):printer_(printer){}virtual int svc(void){ACE_DEBUG((LM_DEBUG,ACE_TEXT("Person(%t) is running\n"))); for (int i=0;i<4;++i){this->printer_.print(i);}return 0;}private:Printer& printer_;};int main(int argc, char *argv[]){Printer printer_obj;Person person1(printer_obj);Person person2(printer_obj);person1.activate();person2.activate();person1.wait();person1.wait();return 0;}

其他库

（std、boost等基本接口都是如此，可以触类旁通）