关于在并行区域内使用关键的 OpenMP,我似乎严重缺乏了解。我的问题很简单:为什么下面的代码会产生带有 valgrind drd 的警告?
#include <stdio.h>
#include <unistd.h>
void A(int* a)
{
printf("a++\n");
(*a)++;
}
void B(int* a)
{
printf("a--\n");
(*a)--;
}
void f(int* a)
{
#pragma omp critical
A(a);
sleep(1); /* work done here */
#pragma omp critical
B(a);
}
int main(int argc, char** argv)
{
int i;
int a = 0;
#pragma omp parallel for
for(i = 0; i < 4; ++i)
{
f(&a);
}
return 0;
}
它是用以下方式编译的:
gcc -fopenmp -g -o omptest omptest.c
valgrind 调用是
valgrind --tool=drd --check-stack-var=yes ./omptest
我的理解是关键部分应该保护我免受我收到的警告的影响。我现在花了 2 天时间试图找出错误,但我没有找到它。如果有人能给我一个关于我到底不明白的东西的提示,那就太好了。
任何帮助表示赞赏。
编辑: 我的 2 CPU 机器上的(重复)警告是:
Thread 2:
Conflicting load by thread 2 at 0x7fefffecc size 4
at 0x4007DE: A (omptest.c:7)
by 0x40082E: f (omptest.c:19)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x4E45EE9: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x4C2D9E1: ??? (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x5053E99: start_thread (pthread_create.c:308)
by 0x535B39C: clone (clone.S:112)
Allocation context: unknown.
Other segment start (thread 1)
at 0x4C2DF29: pthread_create@* (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x4E4631B: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x400889: main (omptest.c:32)
Other segment end (thread 1)
at 0x5326F1D: ??? (syscall-template.S:82)
by 0x5326DBB: sleep (sleep.c:138)
by 0x40083D: f (omptest.c:21)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x400895: main (omptest.c:32)
Conflicting store by thread 2 at 0x7fefffecc size 4
at 0x4007E7: A (omptest.c:7)
by 0x40082E: f (omptest.c:19)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x4E45EE9: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x4C2D9E1: ??? (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x5053E99: start_thread (pthread_create.c:308)
by 0x535B39C: clone (clone.S:112)
Allocation context: unknown.
Other segment start (thread 1)
at 0x4C2DF29: pthread_create@* (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x4E4631B: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x400889: main (omptest.c:32)
Other segment end (thread 1)
at 0x5326F1D: ??? (syscall-template.S:82)
by 0x5326DBB: sleep (sleep.c:138)
by 0x40083D: f (omptest.c:21)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x400895: main (omptest.c:32)
Thread 1:
Conflicting load by thread 1 at 0x7fefffecc size 4
at 0x400805: B (omptest.c:13)
by 0x40084E: f (omptest.c:24)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x400895: main (omptest.c:32)
Allocation context: unknown.
Other segment start (thread 2)
at 0x535B361: clone (clone.S:84)
Other segment end (thread 2)
at 0x5326F1D: ??? (syscall-template.S:82)
by 0x5326DBB: sleep (sleep.c:138)
by 0x40083D: f (omptest.c:21)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x4E45EE9: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x4C2D9E1: ??? (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x5053E99: start_thread (pthread_create.c:308)
by 0x535B39C: clone (clone.S:112)
Conflicting store by thread 1 at 0x7fefffecc size 4
at 0x40080E: B (omptest.c:13)
by 0x40084E: f (omptest.c:24)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x400895: main (omptest.c:32)
Allocation context: unknown.
Other segment start (thread 2)
at 0x535B361: clone (clone.S:84)
Other segment end (thread 2)
at 0x5326F1D: ??? (syscall-template.S:82)
by 0x5326DBB: sleep (sleep.c:138)
by 0x40083D: f (omptest.c:21)
by 0x400902: main._omp_fn.0 (omptest.c:35)
by 0x4E45EE9: ??? (in /usr/lib/x86_64-linux-gnu/libgomp.so.1.0.0)
by 0x4C2D9E1: ??? (in /usr/lib/valgrind/vgpreload_drd-amd64-linux.so)
by 0x5053E99: start_thread (pthread_create.c:308)
by 0x535B39C: clone (clone.S:112)
我将警告理解为 a 上的数据竞争,第 7 行和第 13 行是 (*a)-- 和 (*a)++ 调用。