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| .TH MQ_SEND 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| mq_send, mq_timedsend \- send a message to a message queue |
| .SH SYNOPSIS |
| .nf |
| .B #include <mqueue.h> |
| .PP |
| .BI "int mq_send(mqd_t " mqdes ", const char *" msg_ptr , |
| .BI " size_t " msg_len ", unsigned int " msg_prio ); |
| .PP |
| .B #include <time.h> |
| .B #include <mqueue.h> |
| .PP |
| .BI "int mq_timedsend(mqd_t " mqdes ", const char *" msg_ptr , |
| .BI " size_t " msg_len ", unsigned int " msg_prio , |
| .BI " const struct timespec *" abs_timeout ); |
| .fi |
| .PP |
| Link with \fI\-lrt\fP. |
| .PP |
| .ad l |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR mq_timedsend (): |
| .nf |
| _POSIX_C_SOURCE >= 200112L |
| .fi |
| .SH DESCRIPTION |
| .BR mq_send () |
| adds the message pointed to by |
| .I msg_ptr |
| to the message queue referred to by the message queue descriptor |
| .IR mqdes . |
| The |
| .I msg_len |
| argument specifies the length of the message pointed to by |
| .IR msg_ptr ; |
| this length must be less than or equal to the queue's |
| .I mq_msgsize |
| attribute. |
| Zero-length messages are allowed. |
| .PP |
| The |
| .I msg_prio |
| argument is a nonnegative integer that specifies the priority |
| of this message. |
| Messages are placed on the queue in decreasing order of priority, |
| with newer messages of the same priority being placed after |
| older messages with the same priority. |
| See |
| .BR mq_overview (7) |
| for details on the range for the message priority. |
| .PP |
| If the message queue is already full |
| (i.e., the number of messages on the queue equals the queue's |
| .I mq_maxmsg |
| attribute), then, by default, |
| .BR mq_send () |
| blocks until sufficient space becomes available to allow the message |
| to be queued, or until the call is interrupted by a signal handler. |
| If the |
| .B O_NONBLOCK |
| flag is enabled for the message queue description, |
| then the call instead fails immediately with the error |
| .BR EAGAIN . |
| .PP |
| .BR mq_timedsend () |
| behaves just like |
| .BR mq_send (), |
| except that if the queue is full and the |
| .B O_NONBLOCK |
| flag is not enabled for the message queue description, then |
| .I abs_timeout |
| points to a structure which specifies how long the call will block. |
| This value is an absolute timeout in seconds and nanoseconds |
| since the Epoch, 1970-01-01 00:00:00 +0000 (UTC), |
| specified in the following structure: |
| .PP |
| .in +4n |
| .EX |
| struct timespec { |
| time_t tv_sec; /* seconds */ |
| long tv_nsec; /* nanoseconds */ |
| }; |
| .EE |
| .in |
| .PP |
| If the message queue is full, |
| and the timeout has already expired by the time of the call, |
| .BR mq_timedsend () |
| returns immediately. |
| .SH RETURN VALUE |
| On success, |
| .BR mq_send () |
| and |
| .BR mq_timedsend () |
| return zero; on error, \-1 is returned, with |
| .I errno |
| set to indicate the error. |
| .SH ERRORS |
| .TP |
| .B EAGAIN |
| The queue was full, and the |
| .B O_NONBLOCK |
| flag was set for the message queue description referred to by |
| .IR mqdes . |
| .TP |
| .B EBADF |
| The descriptor specified in |
| .I mqdes |
| was invalid or not opened for writing. |
| .TP |
| .B EINTR |
| The call was interrupted by a signal handler; see |
| .BR signal (7). |
| .TP |
| .B EINVAL |
| The call would have blocked, and |
| .I abs_timeout |
| was invalid, either because |
| .I tv_sec |
| was less than zero, or because |
| .I tv_nsec |
| was less than zero or greater than 1000 million. |
| .TP |
| .B EMSGSIZE |
| .I msg_len |
| was greater than the |
| .I mq_msgsize |
| attribute of the message queue. |
| .TP |
| .B ETIMEDOUT |
| The call timed out before a message could be transferred. |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR mq_send (), |
| .BR mq_timedsend () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| POSIX.1-2001, POSIX.1-2008. |
| .SH NOTES |
| On Linux, |
| .BR mq_timedsend () |
| is a system call, and |
| .BR mq_send () |
| is a library function layered on top of that system call. |
| .SH SEE ALSO |
| .BR mq_close (3), |
| .BR mq_getattr (3), |
| .BR mq_notify (3), |
| .BR mq_open (3), |
| .BR mq_receive (3), |
| .BR mq_unlink (3), |
| .BR mq_overview (7), |
| .BR time (7) |