我正在尝试将多进程应用程序迁移到Docker。不同的进程将放在不同的Docker容器中。
应用程序使用共享内存来交换数据和信号量以进行同步。我已经重新编译了Docker,以便不使用IPC名称空间,并且我有效地检查了sudo ipcs -m
共享内存缓冲区是否可以从不同的容器中访问。
问题是信号量不起作用。我编写了这些简单的程序来检查Docker中POSIX信号量的行为:
/* To be compiled with -lpthread */
#include <stdio.h>
#include <fcntl.h>
#include <semaphore.h>
int main(void) {
int ret, val;
sem_t * mySem;
printf("[ONE] Opening the semaphore...\n");
mySem = sem_open("sem1", O_CREAT, 0777, 0);
if (mySem == SEM_FAILED) {
printf("[ONE] Error on sem_open()\n");
return -1;
}
ret = sem_post(mySem);
getchar(); // Awful way to block execution of [ONE] for a while...
printf("[ONE] Waiting for [TWO]...\n");
ret = sem_wait(mySem);
printf("[ONE] Wait ended\n");
ret = sem_unlink("sem1");
printf("[ONE] Semaphore destroyed\n");
return 0;
}
第二个程序是:
/* To be compiled with -lpthread */
#include <stdio.h>
#include <fcntl.h>
#include <semaphore.h>
int main(void) {
int ret;
int val;
sem_t * mySem;
printf("[TWO] Opening the semaphore...\n");
mySem = sem_open("sem1", O_CREAT, 0777, 0);
if (mySem == SEM_FAILED) {
printf("[TWO] Error on sem_open()\n");
return -1;
}
ret = sem_getvalue(mySem, &val);
printf("[TWO] Semaphore's value is %d\n", val);
printf("[TWO] Waiting for [ONE]...\n");
ret = sem_wait(mySem);
printf("[TWO] Wait ended\n");
printf("[ONE] Doing sem_post() on semaphore...\n");
ret = sem_post(mySem);
ret = sem_close(mySem);
printf("[TWO] Semaphore closed\n");
return 0;
}
在两者中,我省略了许多控件,例如if (ret != 0) {...}
,以保持问题的可读性。
我在主机上运行第一个程序,第二个程序在Docker容器中运行。结果是第二个程序永远等待......
问题是:是否有可能以某种方式在 Docker容器之间或容器和主机之间使用POSIX信号量?
答案 0 :(得分:2)
我使用Docker容器之间的共享内存解决了问题,如this question中所述。
以下代码是this tutorial的修改版本。
档案 server.c
/* To be compiled with -lpthread */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <fcntl.h>
#include <semaphore.h>
#define SHM_SIZE 1000
int main(void) {
int shmid;
key_t key;
char *shm;
sem_t * mySem;
/* We'll name our shared memory segment "5678" */
key = 5678;
/* Create the segment.*/
if ((shmid = shmget(key, SHM_SIZE, IPC_CREAT | IPC_EXCL | 0666)) < 0) {
perror("shmget");
exit(1);
}
/* Now we attach the segment to our data space */
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
perror("shmat");
exit(1);
}
/* Create a new semaphore */
mySem = sem_open("sem1", O_CREAT, 0777, 0);
/* Copy the semaphore on the shared memory segment */
memcpy(shm, mySem, sizeof(*mySem));
/* Do stuff ... */
/* REMEMBER TO USE THE SHARED MEMORY SEGMENT */
/* AND NOT THE LOCAL mySem, USE (sem_t*)shm INSTEAD! */
/* Finally, we wait until the other process
* changes the first character of our memory
* to '*', indicating that it has read what
* we put there.
*/
while (*shm != '*')
sleep(1);
/* Mark the memory segment to be destroyed */
shmctl(shmid, IPC_RMID, NULL);
/* Detach of the memory segment */
shmdt(&shm);
sem_unlink("sem1");
return 0;
}
档案 client.c
/* To be compiled with -lpthread */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <fcntl.h>
#include <semaphore.h>
#define SHM_SIZE 1000
int main(void) {
int shmid;
key_t key;
char *shm;
int ret, val;
key = 5678;
if ((shmid = shmget(key, SHM_SIZE, 0666)) < 0) {
perror("shmget");
exit(1);
}
if ((shm = shmat(shmid, NULL, 0)) == (char *) -1) {
perror("shmat");
exit(1);
}
/* SEMAPHORE IS IN THE SHARED MEMORY SEGMENT */
/* USE (sem_t*)shm TO ACCESS IT */
*shm = '*';
shmdt(&shm);
sem_close("sem1");
return 0;
}
由于可读性目的,代码示例错过了很多控件。
我在主机上运行服务器,在Docker容器内运行客户端,并检查是否可以从两个进程访问信号量。