MsgQueueOpen()
QNX SDP8.0C Library ReferenceAPIDeveloper
Associate a client with a kernel message queue
Synopsis:
#include <sys/neutrino.h>
int MsgQueueOpen( rcvid_t rcvid,
int queueid,
uint32_t msgsize,
uint32_t maxmsg,
unsigned oflag );
Arguments:
- rcvid
- The receive ID associated with an open request that a message queue manager has received.
- queueid
- The identifier of the message queue. Specify a non-negative integer to open an existing queue or -1 to create a new queue.
- msgsize
- The maximum size of messages that can be sent or received on the message queue.
- maxmsg
- The maximum number of messages that the message queue can hold.
- oflag
- Flags specifying the behavior of the open operation:
- _IO_FLAG_RD—open the connection for reading.
- _IO_FLAG_WR—open the connection for writing.
- O_NONBLOCK —specify non-blocking queue access.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The MsgQueueOpen() function is used by message queue managers to connect a client to a message queue in response to an mq_open() call. It performs the necessary steps for locating the queue (and creates it if necessary), creates a new connection between the client (identified by rcvid) of the caller and the queue object, and stores the relevant flags for subsequent operations.
To create a new queue (i.e., queueid is -1), a process must have
the msg_queue ability. For more information, go to Abilities Reference
in the QNX OS
System Security Guide.
Returns:
- ≥0
- If the queueid argument was -1, the ID of the newly created message queue. Otherwise, 0 to indicate that the queue specified by queueid was successfully opened.
- -1
- An error occurred (errno is set).
Errors:
- EBUSY
- The client connection identified by rcvid is already associated with a queue.
- EINVAL
- An argument was invalid.
- ENOSPC
- There's insufficient memory for a new queue.
- EPERM
- The process tried to create a new queue without having the required permission; go to
go to
Abilities Reference
in the QNX OS System Security Guide. - ESRCH
- One of the following is true:
- The queue specified by queueid doesn't exist.
- The rcvid value does not identify an existing client for the message queue.
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |
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