我正在测试在另一个线程中锁定文件描述符是否会影响主线程。
#include <iostream>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <sys/types.h>
//#include <share.h>
#include <stdio.h>
#include <pthread.h>
#include <errno.h>
void *print_message_function( void *ptr );
pthread_mutex_t mut = PTHREAD_MUTEX_INITIALIZER;
int main (int argc, char * const argv[]) {
pthread_t thread1, thread2;
const char *message1 = "Thread 1";
const char *message2 = "Thread 2";
int iret1, iret2;
iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message1);
if(iret2)
{
fprintf(stderr,"Error - pthread_create() return code: %d\n",iret2);
fflush(stdout);
exit(EXIT_FAILURE);
}
printf("pthread_create() for thread 2 returns: %d\n",iret2);
pthread_mutex_lock(&mut);
sleep(1);
std::cout<<"Enter any key:"<<std::endl;
std::cin >> input;
if (fd2 = open( "file1", O_RDWR | O_CREAT | O_TRUNC, 0700 | 0x10) == -1)
{
perror("Cannot open file 2.\n");
fflush(stdout);
}
else
{
printf("File was opened 2!!\n");
fflush(stdout);
if(flock(fd2, LOCK_NB | LOCK_EX)==0)
{
printf("THE FILE WAS LOCKED 2.\n");
}
else if(errno == EAGAIN)
{
printf("The file is locked 2. Resource temporarily unavailable.\n");
}
}
pthread_mutex_unlock(&mut);
close(fd2);
std::cout<<"File closed."<<std::endl;
std::cin >> input;
return 0;
}
void *print_message_function( void *ptr )
{
char *message;
message = (char *) ptr;
printf("%s \n", message);
fflush(stdout);
int fd1;
if ((fd1 = open( "file1", O_RDWR | O_CREAT | O_TRUNC, 0700 | 0x10)) == -1)
{
perror("thread: Cannot open file 1.\n");
fflush(stdout);
//std::cin >> input;
}
else
{
printf("File was opened 1!!\n");
fflush(stdout);
if(flock(fd1, LOCK_NB | LOCK_EX)==0)
{
printf("THE FILE WAS LOCKED 1.\n");
}
else if(errno == EAGAIN)
{
printf("The file is locked 1. Resource temporarily unavailable.\n");
}
}
pthread_mutex_lock(&mut);
pthread_mutex_unlock(&mut);
printf("End of thread.\n");
}
输出结果:
[Session started at 2014-11-26 17:46:16 +0000.]
pthread_create() for thread 2 returns: 0
Thread 1
File was opened 1!!
THE FILE WAS LOCKED 1.
Enter any key:
1
File was opened 2!!
THE FILE WAS LOCKED 2.
File closed.
End of thread.
我不明白为什么在线程内使用flock()不能防止主线程使用flock()获得锁。
根据linux man手册:
由flock()创建的锁与打开的文件描述符相关联,这意味着重复的文件描述符(例如通过fork(2)或dup(2)创建的)引用相同的锁,并且可以使用任何这些描述符修改或释放此锁。此外,该锁是通过任何这些重复描述符上的显式LOCK_UN操作或关闭所有这样的描述符来释放的。
flock()
可能会相互阻塞。 - John Bollinger