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**已解决：在我的类的构造函数中，我有一个Semaphore的构造赛车，它的线程构造是在其中我首先创建Semaphore，然后是Thread的第二个构造。为我工作的解决方案是首先在基类中创建Semaphore，这样我可以在派生类中依赖它。 **为什么这个代码在valgrind（helgrind）下失败？
我有一个相当小的pthreads C++程序，它在正常情况下工作正常。但是，在程序中使用valgrind的线程错误检查工具时，它似乎会发现竞争状态。这种竞争条件特别难以避免的是它发生在“Semaphore”类（它实际上只是封装了sem_init，sem_wait和sem_post）内，所以我不能用另一个Semaphore来解决这个问题（并且不应该）。我不认为valgrind会给出误报，因为我的程序在valgrind下运行时显示不同的行为。
这里的Semaphore.cpp *：
#include "Semaphore.h"
#include <stdexcept>
#include <errno.h>
#include <iostream>
Semaphore::Semaphore(bool pshared,int initial)
: m_Sem(new sem_t())
{
if(m_Sem==0)
throw std::runtime_error("Semaphore constructor error: m_Sem == 0");
if(sem_init(m_Sem,(pshared?1:0),initial)==-1)
throw std::runtime_error("sem_init failed");
}
Semaphore::~Semaphore()
{
sem_destroy(m_Sem);
delete m_Sem;
}
void Semaphore::lock()
{
if(m_Sem==0)
throw std::runtime_error("Semaphore::lock error: m_Sem == 0");
int rc;
for(;;){
rc = sem_wait(m_Sem);
if(rc==0) break;
if(errno==EINTR) continue;
throw std::runtime_error("sem_wait failed");
}
}
void Semaphore::unlock()
{
if(sem_post(m_Sem)!=0)
throw std::runtime_error("sem_post failed");
}
- 注意信号灯的构造如何创建一个名为“m_Sem”新sem_t，并在m_Sem还是等于0。这只是极，情况不太可能发生抛出异常意味着这个构造函数不应该允许m_Sem等于0.好吧...继续到Semaphore :: lock：无论从哪个线程调用此函数（以及构造函数），它都应该 - 理论上 - 对于m_Sem是不可能的，对吧？那么，当我在helgrind下运行我的程序时，Semaphore :: lock肯定会导致抛出这个异常“Semaphore :: lock error：m_Sem == 0”，我真的认为这应该是不可能的。
我在其他程序中使用这个Semaphore类，通过helgrind没有问题，我真的不知道我在这里做什么特别是造成这个问题。根据helgrind的说法，竞赛发生在一个线程的Semaphore构造函数写入和另一个线程的Semaphore :: lock读取之间。说实话，我什至不知道这是怎么可能的：一个对象的方法如何与该对象的构造函数有竞争条件？ C++没有保证在可以调用对象的方法之前调用构造函数？即使在多线程的环境中，这又怎么会被违反呢？
无论如何，现在为valgrind输出。我正在使用valgind版本“Valgrind-3.6.0.SVN-Debian”。 Memcheck说一切都很好。下面是helgrind结果：
$ valgrind --tool=helgrind --read-var-info=yes ./try ==7776== Helgrind, a thread error detector ==7776== Copyright (C) 2007-2009, and GNU GPL'd, by OpenWorks LLP et al. ==7776== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info ==7776== Command: ./try ==7776== terminate called after throwing an instance of '==7776== Thread #1 is the program's root thread ==7776== ==7776== Thread #2 was created ==7776== at 0x425FA38: clone (clone.S:111) ==7776== by 0x40430EA: [email protected]@GLIBC_2.1 (createthread.c:249) ==7776== by 0x402950C: pthread_create_WRK (hg_intercepts.c:230) ==7776== by 0x40295A0: [email protected]* (hg_intercepts.c:257) ==7776== by 0x804CD91: Thread::Thread(void* (*)(void*), void*) (Thread.cpp:10) ==7776== by 0x804B2D5: ActionQueue::ActionQueue() (ActionQueue.h:40) ==7776== by 0x80497CA: main (try.cpp:9) ==7776== ==7776== Possible data race during write of size 4 at 0x42ee04c by thread #1 ==7776== at 0x804D9C5: Semaphore::Semaphore(bool, int) (Semaphore.cpp:8) ==7776== by 0x804B333: ActionQueue::ActionQueue() (ActionQueue.h:40) ==7776== by 0x80497CA: main (try.cpp:9) ==7776== This conflicts with a previous read of size 4 by thread #2 ==7776== at 0x804D75B: Semaphore::lock() (Semaphore.cpp:26) ==7776== by 0x804B3BE: Lock::Lock(Semaphore&) (Lock.h:17) ==7776== by 0x804B497: ActionQueue::ActionQueueLoop() (ActionQueue.h:56) ==7776== by 0x8049ED5: void* CallMemFun, &(ActionQueue::ActionQueueLoop())>(void*) (CallMemFun.h:7) ==7776== by 0x402961F: mythread_wrapper (hg_intercepts.c:202) ==7776== by 0x404296D: start_thread (pthread_create.c:300) ==7776== by 0x425FA4D: clone (clone.S:130) ==7776== std::runtime_error' what(): Semaphore::lock error: m_Sem == 0 ==7776== ==7776== For counts of detected and suppressed errors, rerun with: -v ==7776== Use --history-level=approx or =none to gain increased speed, at ==7776== the cost of reduced accuracy of conflicting-access information ==7776== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 5 from 5)
任何人使用Git和的valgrind可以从我的混帐回购分支检查出的代码（其中，备案，目前正在对提交262369c2d25eb17a0147）如下重现此：
$ git clone git://github.com/notfed/concqueue -b semaphores $ cd concqueue $ make $ valgrind --tool=helgrind --read-var-info=yes ./try