我的环境:
- CentOS 6.5(64位内核)
- 海湾合作委员会 4.4.7 20120313
我正在尝试设置 POSIX 消息队列的属性,但代码不会更改该属性。
我只获得默认属性值。
你能指出我的代码有什么问题吗?
我以用户(而不是 root)身份执行 a.out。
#include <stdio.h>
#include <mqueue.h> // for message queue
#include <sys/stat.h>
#include <stdlib.h> // for EXIT_FAILURE
#include <string.h>
/*
gcc [file] -lrt
*/
static void showAttr(mqd_t mqd)
{
struct mq_attr attr;
mq_getattr(mqd, &attr);
printf("maxmsg = %d\n", attr.mq_maxmsg);
printf("msgsize = %d\n", attr.mq_msgsize);
printf("curmsgs = %d\n", attr.mq_curmsgs);
}
int main()
{
mqd_t mqd;
int flags;
int ret;
struct mq_attr attr;
flags = O_RDWR | O_CREAT;
attr.mq_flags = 0; // or O_NONBLOCK
attr.mq_maxmsg = 60;
attr.mq_msgsize = 120;
attr.mq_curmsgs = 0;
// POSIX IPC name should start with "/"
mqd = mq_open("/mq", flags,
// (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH),
0644,
&attr );
if (mqd < 0) {
printf("open failed\n");
exit(EXIT_FAILURE);
}
printf("open ok\n");
sleep(1);
showAttr(mqd);
ret = mq_close(mqd);
if (ret != 0) {
printf("open failed\n");
exit(EXIT_FAILURE);
}
printf("close ok\n");
return 0;
}
我发现以下代码有效。
但是,当我尝试设置 attr.mq_maxmsg (=60) 时,mq_open 失败。
#include <stdio.h>
#include <mqueue.h> // for message queue
#include <sys/stat.h>
#include <stdlib.h> // for EXIT_FAILURE
#include <string.h>
#include <errno.h>
/*
gcc [file] -lrt
*/
static void showAttr(mqd_t mqd)
{
struct mq_attr attr;
mq_getattr(mqd, &attr);
printf("maxmsg = %d\n", attr.mq_maxmsg);
printf("msgsize = %d\n", attr.mq_msgsize);
printf("curmsgs = %d\n", attr.mq_curmsgs);
}
int main()
{
mqd_t mqd;
int flags;
int ret;
struct mq_attr attr;
flags = O_RDWR | O_CREAT;
// POSIX IPC name should start with "/"
// 1. once open without attribute setting
mqd = mq_open("/mq", flags,
(S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH) );
mq_getattr(mqd, &attr);
mq_unlink("/mq");
mq_close(mqd);
// 2. set values of attribute
// attr.mq_maxmsg = 10;
attr.mq_msgsize = 120;
// 3. allocate attribute
mqd = mq_open("/mq", flags,
(S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH),
// 0644,
&attr );
if (mqd < 0) {
printf("open failed %d\n", mqd);
exit(EXIT_FAILURE);
}
printf("open ok\n");
sleep(1);
showAttr(mqd);
ret = mq_close(mqd);
if (ret != 0) {
printf("open failed\n");
exit(EXIT_FAILURE);
}
printf("close ok\n");
return 0;
}