C语言 valgrind中的helgrind抱怨使用简单互斥锁

carvr3hs  于 2022-12-03  发布在  其他
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我正在调试一些线程代码，并且正在使用valgrind --tool=helgrind，由于某种原因，helgrind不喜欢下面的简单示例。
在启动一个线程之前，我会锁定互斥锁，在线程结束时，我会解锁互斥锁，从而确保一次只能运行一个线程，因为我假设互斥锁会一直被锁定到线程结束。
为什么根据valgrind，这是无效的？
这是一个更大程序的一部分，我的主程序正在阅读/解析数据，它将启动一个分析线程，但我只希望一次运行一个分析线程。

#include <pthread.h>
#include <stdio.h>

pthread_mutex_t mutex;

void *inner(void *ptr){
  size_t threadid=(size_t)ptr;
  int sleepval = lrand48() % 5 +1;
  fprintf(stderr,"thread: %lu will wait:%d\n",threadid,sleepval);fflush(stderr);  
  sleep(sleepval);
  pthread_mutex_unlock(&mutex);
}



int outer(size_t ntimes){
  pthread_t thread1;
  size_t i;
  for(i=0;i<ntimes;i++){
    pthread_mutex_lock(&mutex);
    if(pthread_create( &thread1, NULL, inner, (void*) i))
      fprintf(stderr,"Problems creating thread\n");
  }
    pthread_mutex_lock(&mutex);
    pthread_mutex_unlock(&mutex);
}

int main(){
  pthread_mutex_init(&mutex, NULL);
  outer(3);
  return 0;
}

==8326== Helgrind, a thread error detector
==8326== Copyright (C) 2007-2013, and GNU GPL'd, by OpenWorks LLP et al.
==8326== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==8326== Command: ./a.out
==8326== 
thread: 0 will wait:1
==8326== ---Thread-Announcement------------------------------------------
==8326== 
==8326== Thread #1 is the program's root thread
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #1: Attempt to re-lock a non-recursive lock I already hold
==8326==    at 0x4C32010: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400959: outer (threadTest.c:21)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326==  Lock was previously acquired
==8326==    at 0x4C32145: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400959: outer (threadTest.c:21)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== ---Thread-Announcement------------------------------------------
==8326== 
==8326== Thread #2 was created
==8326==    at 0x515543E: clone (clone.S:74)
==8326==    by 0x4E44199: do_clone.constprop.3 (createthread.c:75)
==8326==    by 0x4E458BA: pthread_create@@GLIBC_2.2.5 (createthread.c:245)
==8326==    by 0x4C30C90: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400976: outer (threadTest.c:22)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #2 unlocked lock at 0x6010A0 currently held by thread #1
==8326==    at 0x4C325C0: pthread_mutex_unlock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400937: inner (threadTest.c:11)
==8326==    by 0x4C30E26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4E45181: start_thread (pthread_create.c:312)
==8326==    by 0x515547C: clone (clone.S:111)
==8326==   Lock at 0x6010A0 was first observed
==8326==    at 0x4C31DDA: pthread_mutex_init (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4009D0: main (threadTest.c:31)
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #1: Bug in libpthread: recursive write lock granted on mutex/wrlock which does not support recursion
==8326==    at 0x4C32145: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400959: outer (threadTest.c:21)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
thread: 1 will wait:4
==8326== ---Thread-Announcement------------------------------------------
==8326== 
==8326== Thread #3 was created
==8326==    at 0x515543E: clone (clone.S:74)
==8326==    by 0x4E44199: do_clone.constprop.3 (createthread.c:75)
==8326==    by 0x4E458BA: pthread_create@@GLIBC_2.2.5 (createthread.c:245)
==8326==    by 0x4C30C90: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400976: outer (threadTest.c:22)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #3 unlocked lock at 0x6010A0 currently held by thread #1
==8326==    at 0x4C325C0: pthread_mutex_unlock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400937: inner (threadTest.c:11)
==8326==    by 0x4C30E26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4E45181: start_thread (pthread_create.c:312)
==8326==    by 0x515547C: clone (clone.S:111)
==8326==   Lock at 0x6010A0 was first observed
==8326==    at 0x4C31DDA: pthread_mutex_init (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4009D0: main (threadTest.c:31)
==8326== 
thread: 2 will wait:1
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #1: Attempt to re-lock a non-recursive lock I already hold
==8326==    at 0x4C32010: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4009B1: outer (threadTest.c:25)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326==  Lock was previously acquired
==8326==    at 0x4C32145: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400959: outer (threadTest.c:21)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== ---Thread-Announcement------------------------------------------
==8326== 
==8326== Thread #4 was created
==8326==    at 0x515543E: clone (clone.S:74)
==8326==    by 0x4E44199: do_clone.constprop.3 (createthread.c:75)
==8326==    by 0x4E458BA: pthread_create@@GLIBC_2.2.5 (createthread.c:245)
==8326==    by 0x4C30C90: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400976: outer (threadTest.c:22)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #4 unlocked lock at 0x6010A0 currently held by thread #1
==8326==    at 0x4C325C0: pthread_mutex_unlock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x400937: inner (threadTest.c:11)
==8326==    by 0x4C30E26: ??? (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4E45181: start_thread (pthread_create.c:312)
==8326==    by 0x515547C: clone (clone.S:111)
==8326==   Lock at 0x6010A0 was first observed
==8326==    at 0x4C31DDA: pthread_mutex_init (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4009D0: main (threadTest.c:31)
==8326== 
==8326== ----------------------------------------------------------------
==8326== 
==8326== Thread #1: Bug in libpthread: recursive write lock granted on mutex/wrlock which does not support recursion
==8326==    at 0x4C32145: pthread_mutex_lock (in /usr/lib/valgrind/vgpreload_helgrind-amd64-linux.so)
==8326==    by 0x4009B1: outer (threadTest.c:25)
==8326==    by 0x4009DA: main (threadTest.c:32)
==8326== 
==8326== 
==8326== For counts of detected and suppressed errors, rerun with: -v
==8326== Use --history-level=approx or =none to gain increased speed, at
==8326== the cost of reduced accuracy of conflicting-access information
==8326== ERROR SUMMARY: 9 errors from 7 contexts (suppressed: 104 from 61)
c

2条答案

按热度按时间
nnvyjq4y

nnvyjq4y1#

直接的问题是，你在一个线程中锁定了一个互斥锁，然后在另一个线程中解锁它。你还试图在同一个线程中锁定同一个非递归互斥锁两次。由于只有获得锁的线程才能释放它，这将是一个死锁。
要实现您想要的语义，您可以加入新创建的线程：连接将阻塞直到相应的线程退出。
或者，您可以保护活动线程计数，该计数由创建线程递增，并在线程完成时递减。完成线程还将发出条件变量信号。创建线程将检查计数，如果计数太高，则等待条件变量。
拥有一个使用作业队列并可能阻塞作业队列的处理器线程可能是限制工作线程数量的最简单、最有效的方法。

赞(0）分享  回复(0）举报  2022-12-03
svmlkihl

svmlkihl2#

从pthread_mutex_lock的缐上手册：
如果执行绪尝试解除锁定未锁定的Mutex或已解除锁定的Mutex，则会产生未定义的行为。
因此，您必须在同一个线程中锁定和解锁互斥锁。
此外，您的函数应该返回一个与原型匹配的值。

#include <pthread.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>

pthread_mutex_t mutex;

void *inner(void *ptr){
  size_t threadid = *(size_t *)ptr;
  int sleepval = rand() % 5 +1;
  pthread_mutex_lock(&mutex);
  fprintf(stderr,"thread: %lu will wait:%d\n",threadid,sleepval);
  fflush(stderr);
  sleep(sleepval);
  pthread_mutex_unlock(&mutex);
  return NULL;
}

int outer(size_t ntimes){
  pthread_t thread[ntimes];
  size_t i, id[ntimes];
  for(i=0;i<ntimes;i++){
    id[i] = i;
    if(pthread_create(thread + i, NULL, inner, &id[i]))
      fprintf(stderr,"Problems creating thread\n");
  }

  for(i=0;i<ntimes;i++)
    pthread_join(thread[i], NULL);
  return 0;
}

int main(void){

  pthread_mutex_init(&mutex, NULL);
  outer(3);
  return 0;
}

这对我很有效，我还添加了缺少的头文件，并更改了函数参数以满足新的需求。
旁注：outer函数现在使用可变长度数组，所以它只在C99中工作，在C++中不工作（这个问题被标记为两者都有）。

赞(0）分享  回复(0）举报  2022-12-03
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