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**已解決：在我的類的構造函數中，我有一個Semaphore的構造賽車，它的線程構造是在其中我首先創建Semaphore，然後是Thread的第二個構造。爲我工作的解決方案是首先在基類中創建Semaphore，這樣我可以在派生類中依賴它。 **爲什麼這個代碼在valgrind（helgrind）下失敗？
我有一個相當小的pthreads C++程序，它在正常情況下工作正常。但是，在程序中使用valgrind的線程錯誤檢查工具時，它似乎會發現競爭狀態。這種競爭條件特別難以避免的是它發生在「Semaphore」類（它實際上只是封裝了sem_init，sem_wait和sem_post）內，所以我不能用另一個Semaphore來解決這個問題（並且不應該）。我不認爲valgrind會給出誤報，因爲我的程序在valgrind下運行時顯示不同的行爲。
這裏的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");
}
- 注意信號燈的構造如何創建一個名爲「m_Sem」新sem_t，並在m_Sem還是等於0。這只是極，情況不太可能發生拋出異常意味着這個構造函數不應該允許m_Sem等於0.好吧...繼續到Semaphore :: lock：無論從哪個線程調用此函數（以及構造函數），它都應該 - 理論上 - 對於m_Sem是不可能的，對吧？那麼，當我在helgrind下運行我的程序時，Semaphore :: lock肯定會導致拋出這個異常「Semaphore :: lock error：m_Sem == 0」，我真的認爲這應該是不可能的。
我在其他程序中使用這個Semaphore類，通過helgrind沒有問題，我真的不知道我在這裏做什麼特別是造成這個問題。根據helgrind的說法，競賽發生在一個線程的Semaphore構造函數寫入和另一個線程的Semaphore :: lock讀取之間。說實話，我什至不知道這是怎麼可能的：一個對象的方法如何與該對象的構造函數有競爭條件？ C++沒有保證在可以調用對象的方法之前調用構造函數？即使在多線程的環境中，這又怎麼會被違反呢？
無論如何，現在爲valgrind輸出。我正在使用valgind版本「Valgrind-3.6.0.SVN-Debian」。 Memcheck說一切都很好。下面是helgrind結果：
$ 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可以從我的混帳回購分支檢查出的代碼（其中，備案，目前正在對提交262369c2d25eb17a0147）如下重現此：
$ git clone git://github.com/notfed/concqueue -b semaphores $ cd concqueue $ make $ valgrind --tool=helgrind --read-var-info=yes ./try