I am trying to implement posix message queue application. I am faced with an error on the mq_receive section. It says "Message too long". I've tried couple of small tweeks, but to no result. Please do suggest any rectificaitons.
mq_send section-works successfully
mq_receive section: error-Message too long
Hello,
My question is related to "pipcs -qa" command under HP-UX 11i PA-RISC 64 bits.
We have a little C program that creates posix ipc message queues using the mq_open() system function.
The program fail with 'No space left on device' error when we create big queues. What is the system... (6 Replies)
Hi all,
Please tell me how to change POSIX message queue maximum size? "ulimit" is not a solution because it controls shell resources. But i need to control queue size before login in and starting the shell. It is needed to limit queue size for applications started before login in.
Sorry for my... (7 Replies)
Hii can anyone pls tell how to limit the max no of message in a posix message queue. I have made changes in proc/sys/fs/mqueue/msg_max
But still whenever i try to read the value of max. message in the queue using attr.mq_curmsgs (where struct mq_attr attr) its giving the default value as 10.... (0 Replies)
Hi
I have a log file which contain XML message. I want to extract the value between the tag : <businessEventId>13201330</businessEventId> i.e., 13201330.
I tried the following commands but as the message is very long, unable to do it. Attached is the log file. Please provide inputs.
--... (3 Replies)
in a single main() function,so need signal handling. Use Posix Message Queue IPC mechanism , can ignore the priority and other linked list message,to implement the scenario:
client:Knock Knock
server:who's there
client: Eric
Server:Eric,Welcome.
client:exit
all process terminated
... (1 Reply)
Hi,
I wanted to know whether the POSIX message queues are statically allocated memory by the kernel based on the parameters specified in the open or as and when we send messages, memory are allocated?
Does the kernel reserve the specified memory for the message queue irrespective of whether... (1 Reply)
hello, I try to test the POSIX mq_open function on book unp like below:
#include "unpipc.h"
# include <mqueue.h>
int main(int argc, char **argv)
{
int c, flags;
mqd_t mqd;
flags = O_RDWR | O_CREAT;
while ((c = getopt(argc, argv, "e")) != -1) {
... (3 Replies)
I have a ksh script (script1) that calls another ksh script (script2). If script2.ksh hangs or takes too long to execute I want script1.ksh to kill the call to script2.ksh and instead just display "Script2 can't run right now". Could someone help me with coding this? (1 Reply)
Discussion started by: mrskittles99
1 Replies
LEARN ABOUT OPENDARWIN
mq_setattr
MQ_GETATTR(3) Linux Programmer's Manual MQ_GETATTR(3)NAME
mq_getattr, mq_setattr - get/set message queue attributes
SYNOPSIS
#include <mqueue.h>
int mq_getattr(mqd_t mqdes, struct mq_attr *attr);
int mq_setattr(mqd_t mqdes, const struct mq_attr *newattr,
struct mq_attr *oldattr);
Link with -lrt.
DESCRIPTION
mq_getattr() and mq_setattr() respectively retrieve and modify attributes of the message queue referred to by the message queue descriptor
mqdes.
mq_getattr() returns an mq_attr structure in the buffer pointed by attr. This structure is defined as:
struct mq_attr {
long mq_flags; /* Flags: 0 or O_NONBLOCK */
long mq_maxmsg; /* Max. # of messages on queue */
long mq_msgsize; /* Max. message size (bytes) */
long mq_curmsgs; /* # of messages currently in queue */
};
The mq_flags field contains flags associated with the open message queue description. This field is initialized when the queue is created
by mq_open(3). The only flag that can appear in this field is O_NONBLOCK.
The mq_maxmsg and mq_msgsize fields are set when the message queue is created by mq_open(3). The mq_maxmsg field is an upper limit on the
number of messages that may be placed on the queue using mq_send(3). The mq_msgsize field is an upper limit on the size of messages that
may be placed on the queue. Both of these fields must have a value greater than zero. Two /proc files that place ceilings on the values
for these fields are described in mq_overview(7).
The mq_curmsgs field returns the number of messages currently held in the queue.
mq_setattr() sets message queue attributes using information supplied in the mq_attr structure pointed to by newattr. The only attribute
that can be modified is the setting of the O_NONBLOCK flag in mq_flags. The other fields in newattr are ignored. If the oldattr field is
not NULL, then the buffer that it points to is used to return an mq_attr structure that contains the same information that is returned by
mq_getattr().
RETURN VALUE
On success mq_getattr() and mq_setattr() return 0; on error, -1 is returned, with errno set to indicate the error.
ERRORS
EBADF The message queue descriptor specified in mqdes is invalid.
EINVAL newattr->mq_flags contained set bits other than O_NONBLOCK.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
+---------------------------+---------------+---------+
|Interface | Attribute | Value |
+---------------------------+---------------+---------+
|mq_getattr(), mq_setattr() | Thread safety | MT-Safe |
+---------------------------+---------------+---------+
CONFORMING TO
POSIX.1-2001, POSIX.1-2008.
NOTES
On Linux, mq_getattr() and mq_setattr() are library functions layered on top of the mq_getsetattr(2) system call.
EXAMPLE
The program below can be used to show the default mq_maxmsg and mq_msgsize values that are assigned to a message queue that is created with
a call to mq_open(3) in which the attr argument is NULL. Here is an example run of the program:
$ ./a.out /testq
Maximum # of messages on queue: 10
Maximum message size: 8192
Since Linux 3.5, the following /proc files (described in mq_overview(7)) can be used to control the defaults:
$ uname -sr
Linux 3.8.0
$ cat /proc/sys/fs/mqueue/msg_default
10
$ cat /proc/sys/fs/mqueue/msgsize_default
8192
Program source
#include <mqueue.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE);
} while (0)
int
main(int argc, char *argv[])
{
mqd_t mqd;
struct mq_attr attr;
if (argc != 2) {
fprintf(stderr, "Usage: %s mq-name
", argv[0]);
exit(EXIT_FAILURE);
}
mqd = mq_open(argv[1], O_CREAT | O_EXCL, S_IRUSR | S_IWUSR, NULL);
if (mqd == (mqd_t) -1)
errExit("mq_open");
if (mq_getattr(mqd, &attr) == -1)
errExit("mq_getattr");
printf("Maximum # of messages on queue: %ld
", attr.mq_maxmsg);
printf("Maximum message size: %ld
", attr.mq_msgsize);
if (mq_unlink(argv[1]) == -1)
errExit("mq_unlink");
exit(EXIT_SUCCESS);
}
SEE ALSO mq_close(3), mq_notify(3), mq_open(3), mq_receive(3), mq_send(3), mq_unlink(3), mq_overview(7)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the
latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 MQ_GETATTR(3)