Valgrind的多线程调试工具

Valgrind的多线程调试工具
Helgrind是Valgrind的一个重点功能本节主要针对与多线程基本安全问题进行检测：【所有的代码环境都是在POSIX_THREAD模式下】

写线程代码时经常碰到如下问题
1) 资源不安全访问【就是多个线程在没有同步的情况下写某个资源体】
2) 死锁问题
3) POSIX pthreads API的错误使用
4) 在前面几个基础上都能安全无误的情况下多于多线程程序就是要能够能好将同步块尽量缩到最小【这是一个很大的课题】
解决问题：
问题1: 调用Helgrind能够很好的解决掉已基本例子为例：

#include <pthread.h>
int var = 0;
void* child_fn ( void* arg ) {
var++;
return NULL;
}
int main ( void ) {
pthread_t child;
pthread_t child2;
pthread_create(&child,NULL, child_fn, NULL);
pthread_create(&child2,NULL,child_fn,NULL);
pthread_join(child,NULL);
pthread_join(child2,NULL);
return 0;
}

明显var是共享的不安全访问，调用Helgrind看看怎么能够检测出来
gcc -g thread_helgrind.c -o thread_helgrind -lpthread
valgrind --tool=helgrind ./thread_helgrind
可以看出valgrind弹出如下输出信息：

==25516== Helgrind, a thread error detector

==25516== Using Valgrind-3.9.0 and LibVEX; rerun with -h for copyright info

==25516== Command: ./thread_helgrind

==25516==

==25516== ---Thread-Announcement------------------------------------------

==25516==

==25516== Thread #3 was created

==25516== at 0x415B3C8: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== ---Thread-Announcement------------------------------------------

==25516==

==25516== Thread #2 was created

==25516== at 0x415B3C8: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== ----------------------------------------------------------------

==25516==

==25516== Possible data race during read of size 4 at 0x804A028 by thread #3

==25516== Locks held: none

==25516== at 0x804851F: child_fn (thread_helgrind.c:12)

==25516== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==25516== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==25516== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== This conflicts with a previous write of size 4 by thread #2

==25516== Locks held: none

==25516== at 0x8048527: child_fn (thread_helgrind.c:12)

==25516== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==25516== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==25516== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== ----------------------------------------------------------------

==25516==

==25516== Possible data race during write of size 4 at 0x804A028 by thread #3

==25516== Locks held: none

==25516== at 0x8048527: child_fn (thread_helgrind.c:12)

==25516== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==25516== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==25516== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== This conflicts with a previous write of size 4 by thread #2

==25516== Locks held: none

==25516== at 0x8048527: child_fn (thread_helgrind.c:12)

==25516== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==25516== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==25516== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==25516==

==25516== For counts of detected and suppressed errors, rerun with: -v

==25516== Use --history-level=approx or =none to gain increased speed, at

==25516== the cost of reduced accuracy of conflicting-access information

==25516== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)

可以看出绿色就显示的data_race错误可以直接定位到var前后没有locks/

问题2:
    死锁问题是尽量避免对于helgrind可以检测出加锁解锁顺序出现问题导致的死锁问题    这个问题我们可以好好看下：
    首先看下一个正常的程序

#include <pthread.h>

pthread_mutex_t mut_thread;

int var = 0;

void* child_fn ( void* arg ) {

pthread_mutex_lock(&mut_thread);

var++;

pthread_mutex_unlock(&mut_thread);

return NULL;

}

int main ( void ) {

pthread_t child;

pthread_t child2;

pthread_mutex_init(&mut_thread,NULL);

pthread_create(&child,NULL, child_fn, NULL);

pthread_create(&child2,NULL,child_fn,NULL);

pthread_join(child,NULL);

pthread_join(child2,NULL);

return 0;

}

正常加锁解锁没有问题
在看下连续加2次锁的情况：

#include <pthread.h>

pthread_mutex_t mut_thread;

int var = 0;

void* child_fn ( void* arg ) {

pthread_mutex_lock(&mut_thread);

var++;

pthread_mutex_lock(&mut_thread);

return NULL;

}

int main ( void ) {

pthread_t child;

pthread_t child2;

pthread_mutex_init(&mut_thread,NULL);

pthread_create(&child,NULL, child_fn, NULL);

pthread_create(&child2,NULL,child_fn,NULL);

pthread_join(child,NULL);

pthread_join(child2,NULL);

return 0;

}

看下这个helgrind打印出来的东西【当然要杀死不然会一直卡在那里动都不动一下】

==26534== Helgrind, a thread error detector

==26534== Using Valgrind-3.9.0 and LibVEX; rerun with -h for copyright info

==26534== Command: ./deadlock_helgrind

==26534==

==26534== ---Thread-Announcement------------------------------------------

==26534==

==26534== Thread #2 was created

==26534== at 0x415B3C8: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26534==

==26534== ----------------------------------------------------------------

==26534==

==26534== Thread #2: Attempt to re-lock a non-recursive lock I already hold

==26534== at 0x402E8E5: pthread_mutex_lock (hg_intercepts.c:507)

==26534== by 0x80485C6: child_fn (deadlock_helgrind.c:14)

==26534== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26534== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26534== Lock was previously acquired

==26534== at 0x402E95D: pthread_mutex_lock (hg_intercepts.c:518)

==26534== by 0x80485AD: child_fn (deadlock_helgrind.c:12)

==26534== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26534== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26534==

^C==26534== ----------------------------------------------------------------

==26534==

==26534== Thread #2: Exiting thread still holds 1 lock

==26534== at 0x4001182: ??? (in /lib/i386-linux-gnu/ld-2.17.so)

==26534== by 0x405B4D1: __lll_lock_wait (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x4056ED3: _L_lock_776 (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x4056D11: pthread_mutex_lock (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x402E914: pthread_mutex_lock (hg_intercepts.c:510)

==26534== by 0x80485C6: child_fn (deadlock_helgrind.c:14)

==26534== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26534== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26534== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26534==

==26534== For counts of detected and suppressed errors, rerun with: -v

==26534== Use --history-level=approx or =none to gain increased speed, at

==26534== the cost of reduced accuracy of conflicting-access information

==26534== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0
Lock was previously acquired 对于自身线程来讲这样的做法明显出问题它自身还在尝试获取这个lock 这样就导致死锁的发生。可以定位到==26534== by 0x80485C6: child_fn (deadlock_helgrind.c:14)出问题了所以这个helgrind解决这类问题时还是非常的厉害的~！
接下来看一个2 mutex导致的问题：

#include <pthread.h>

pthread_mutex_t mut_thread;

pthread_mutex_t mut_thread1;

int var = 0;

void* child_fn ( void* arg ) {

pthread_mutex_lock(&mut_thread);

pthread_mutex_lock(&mut_thread1);

var++;

pthread_mutex_unlock(&mut_thread);

pthread_mutex_unlock(&mut_thread1);

return NULL;

}

void* child_fn1(void *arg)

{

pthread_mutex_lock(&mut_thread1);

pthread_mutex_lock(&mut_thread);

var++;

pthread_mutex_unlock(&mut_thread1);

pthread_mutex_unlock(&mut_thread);

return NULL;

}

int main ( void ) {

pthread_t child;

pthread_t child2;

pthread_mutex_init(&mut_thread,NULL);

pthread_mutex_init(&mut_thread1,NULL);

pthread_create(&child,NULL, child_fn, NULL);

pthread_create(&child2,NULL,child_fn1,NULL);

pthread_join(child,NULL);

pthread_join(child2,NULL);

return 0;

}

加锁顺序导致死锁问题

==26785== Helgrind, a thread error detector

==26785== Using Valgrind-3.9.0 and LibVEX; rerun with -h for copyright info

==26785== Command: ./deadlock_helgrind

==26785==

==26785== ---Thread-Announcement------------------------------------------

==26785==

==26785== Thread #3 was created

==26785== at 0x415B3C8: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26785==

==26785== ----------------------------------------------------------------

==26785==

==26785== Thread #3: lock order "0x804A038 before 0x804A050" violated

==26785==

==26785== Observed (incorrect) order is: acquisition of lock at 0x804A050

==26785== at 0x402E95D: pthread_mutex_lock (hg_intercepts.c:518)

==26785== by 0x8048637: child_fn1 (deadlock_helgrind.c:22)

==26785== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26785== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26785== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26785==

==26785== followed by a later acquisition of lock at 0x804A038

==26785== at 0x402E95D: pthread_mutex_lock (hg_intercepts.c:518)

==26785== by 0x8048643: child_fn1 (deadlock_helgrind.c:23)

==26785== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26785== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26785== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26785==

==26785== Required order was established by acquisition of lock at 0x804A038

==26785== at 0x402E95D: pthread_mutex_lock (hg_intercepts.c:518)

==26785== by 0x80485ED: child_fn (deadlock_helgrind.c:13)

==26785== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26785== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26785== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26785==

==26785== followed by a later acquisition of lock at 0x804A050

==26785== at 0x402E95D: pthread_mutex_lock (hg_intercepts.c:518)

==26785== by 0x80485F9: child_fn (deadlock_helgrind.c:14)

==26785== by 0x402E5F6: mythread_wrapper (hg_intercepts.c:233)

==26785== by 0x4054D77: start_thread (in /lib/i386-linux-gnu/libpthread-2.17.so)

==26785== by 0x415B3DD: clone (in /lib/i386-linux-gnu/libc-2.17.so)

==26785==

==26785== For counts of detected and suppressed errors, rerun with: -v

==26785== Use --history-level=approx or =none to gain increased speed, at

==26785== the cost of reduced accuracy of conflicting-access information

==26785== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 9 from 9

这是观察法得出的加锁顺序出错导致了这种情况的发生。
posix_thread erro这里就不列举了这个完全是看基础。

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