我正在调试一些线程代码，并使用valgrind --tool = helgrind，由于某种原因，helgrind不喜欢下面的简单示例。
在我开始一个线程之前，我锁定了互斥锁。在我解锁的线程的最后，通过假设互斥锁将被锁定直到线程完成，确保一次只能运行一个线程。
根据valgrind，这为什么无效？
这是一个更大程序的一部分，我的主程序正在读取/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)
答案 0 :(得分：2)
来自pthread_mutex_lock的手册页：
如果线程尝试解锁未锁定的互斥锁或a 解锁的互斥锁，未定义的行为结果。
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;
}
这对我有用。我还添加了缺少的标题并更改了函数参数以匹配新的要求。
附注：outer函数现在使用可变长度数组，因此它仅在C99中工作，而不是在C ++中工作（问题被标记为两者）。
答案 1 :(得分：2)
当前的问题是您在一个线程中锁定互斥锁并在另一个线程中解锁它。您还尝试在同一个线程中两次锁定相同的非递归互斥锁。因为只有获得锁定的线程才能释放它，因为它是一个死锁。
要实现你想要的句子，你可能希望你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，该计数由创建线程增加，并在线程完成时递减。精加工线程也会发出条件变量的信号。如果计数太高，创建线程将检查计数并等待条件变量。
拥有一个使用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。