mq_receive(3) [osf1 man page]
mq_receive(3) Library Functions Manual mq_receive(3) NAME
mq_receive - Receives the oldest, highest-priority message from the message queue (P1003.1b) LIBRARY
Realtime Library (librt.so, librt.a) SYNOPSIS
#include <mqueue.h> ssize_t mq_receive ( mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned int *msg_prio); PARAMETERS
mqdes Specifies a message queue by descriptor. *msg_ptr Specifies a pointer to a buffer to receive the message. msg_len Specifies the size of the receive buffer identified by the msg_ptr argument. *msg_prio Specifies a pointer to a location to receive the message priority. DESCRIPTION
The mq_receive function receives the oldest, highest-priority message from the message queue. The message is removed from the queue and transferred to the buffer pointed to by the msg_ptr argument. If the specified message queue is empty and the O_NONBLOCK flag is not set with the mqdes argument, the mq_receive function blocks until a message is put on the queue or until the mq_receive function is interrupted by a signal. If more than one process is waiting to receive a message when a message arrives at an empty queue, the highest-priority process that has been waiting the longest is selected to receive the message. If the message queue is empty and the O_NONBLOCK flag is set, no message is removed from the queue, and an error is returned. RETURN VALUES
On successful completion, the function returns the length of the selected message. Otherwise, the function returns the value -1 and sets errno to indicate the error. No message is removed from the queue. ERRORS
The mq_receive function fails under the following conditions: [EAGAIN] O_NONBLOCK was set in the message description associated with mqdes, and the specified message queue is empty. [EBADF] The mqdes argument is not a valid message queue descriptor open for reading. [EBADMSG] The implementation has detected a data corruption problem with the message. [EFAULT] An internal virtual memory error occurred. [EINTR] The mq_receive function was interrupted by a signal. [EMSGSIZE] The specified message buffer size, msg_len, is less than the message size attribute of the message queue. RELATED INFORMATION
Functions: mq_send(3) Guide to Realtime Programming delim off mq_receive(3)
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mq_receive(3C) Standard C Library Functions mq_receive(3C) NAME
mq_receive, mq_timedreceive, mq_reltimedreceive_np - receive a message from a message queue SYNOPSIS
#include <mqueue.h> ssize_t mq_receive(mqd_t mqdes, char *msg_ptr, size_t msg_len, unsigned *msg_prio); #include <mqueue.h> #include <time.h> ssize_t mq_timedreceive(mqd_t mqdes, char *restrict msg_ptr, size_t msg_len, unsigned *restrict msg_prio, const struct timespec *restrict abs_timeout); ssize_t mq_reltimedreceive_np(mqd_t mqdes, char *restrict msg_ptr, size_t msg_len, unsigned *restrict msg_prio, const struct timespec *restrict rel_timeout); DESCRIPTION
The mq_receive() function receives the oldest of the highest priority message(s) from the message queue specified by mqdes. If the size of the buffer in bytes, specified by msg_len, is less than the mq_msgsize member of the message queue, the function fails and returns an error. Otherwise, the selected message is removed from the queue and copied to the buffer pointed to by msg_ptr. If the value of msg_len is greater than {SSIZE_MAX}, the result is implementation-defined. If msg_prio is not NULL, the priority of the selected message is stored in the location referenced by msg_prio. If the specified message queue is empty and O_NONBLOCK is not set in the message queue description associated with mqdes, (see mq_open(3C) and mq_setattr(3C)), mq_receive() blocks, waiting until a message is enqueued on the message queue, or until mq_receive() is interrupted by a signal. If more than one process (or thread) is waiting to receive a message when a message arrives at an empty queue, then the process of highest priority that has been waiting the longest is selected to receive the message. If the specified message queue is empty and O_NONBLOCK is set in the message queue description associated with mqdes, no message is removed from the queue, and mq_receive() returns an error. The mq_timedreceive() function receives the oldest of the highest priority messages from the message queue specified by mqdes as described for the mq_receive() function. However, if O_NONBLOCK was not specified when the message queue was opened with the mq_open(3C) function, and no message exists on the queue to satisfy the receive, the wait for such a message is terminated when the specified timeout expires. If O_NONBLOCK is set, this function is equivalent to mq_receive(). The mq_reltimedreceive_np() function is identical to the mq_timedreceive() function, except that the timeout is specified as a relative time interval. For mq_timedreceive(), the timeout expires when the absolute time specified by abs_timeout passes, as measured by the CLOCK_REALTIME clock (that is, when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the call. For mq_reltimedreceive_np(), the timeout expires when the time interval specified by rel_timeout passes, as measured by the CLOCK_REALTIME clock, or if the time interval specified by rel_timeout is negative at the time of the call. The resolution of the timeout is the resolution of the CLOCK_REALTIME clock. The timespec argument is defined in the <time.h> header. Under no circumstance does the operation fail with a timeout if a message can be removed from the message queue immediately. The validity of the timeout parameter need not be checked if a message can be removed from the message queue immediately. RETURN VALUES
Upon successful completion, mq_receive(), mq_timedreceive(), and mq_reltimedreceive_np() return the length of the selected message in bytes and the message is removed from the queue. Otherwise, no message is removed from the queue, the functions return a value of -1, and sets errno to indicate the error condition. ERRORS
The mq_receive(), mq_timedreceive(), and mq_reltimedreceive_np() functions will fail if: EAGAIN O_NONBLOCK was set in the message description associated with mqdes, and the specified message queue is empty. EBADF The mqdes argument is not a valid message queue descriptor open for reading. EINTR The function was interrupted by a signal. EINVAL The process or thread would have blocked, and the timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1,000 million. EMSGSIZE The specified message buffer size, msg_len, is less than the message size member of the message queue. ETIMEDOUT The O_NONBLOCK flag was not set when the message queue was opened, but no message arrived on the queue before the specified timeout expired. The mq_receive(), mq_timedreceive(), and mq_reltimedreceive_np() functions may fail if: EBADMSG A data corruption problem with the message has been detected. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ |ATTRIBUTE TYPE |ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ |Standard |See below. | +-----------------------------+-----------------------------+ For mq_receive() and mq_timedreceive(). see standards(5). SEE ALSO
mqueue.h(3HEAD), mq_open(3C), mq_send(3C), mq_setattr(3C), attributes(5), standards(5) SunOS 5.11 5 Feb 2008 mq_receive(3C)