EmbLogic » Meenakshi Bhardwaj https://www.emblogic.com/blog Embedded System and ARM Training Tue, 03 Mar 2020 13:00:06 +0000 en-US hourly 1 http://wordpress.org/?v=3.9.1 How to create Message Queue https://www.emblogic.com/blog/12/how-to-create-message-queue/ https://www.emblogic.com/blog/12/how-to-create-message-queue/#comments Fri, 09 Dec 2016 12:36:01 +0000 http://www.emblogic.com/blog/?p=13756 Continue reading →]]> The msgget() system call returns the System message queue identifier associated with the value of the key argument. A new message queue is created if key has the value  IPC_PRIVATE or key isn’t IPC_PRIVATE, no message queue with the given key exists, and  IPC_CREAT is specified in msgflg. If msgflg specifies both IPC_CREAT and IPC_EXCL and a message queue already exists for key, then msgget() fails with errno set to EEXIST. This is analogous to the effect of the combination O_CREAT | O_EXCL for open.

These header files are used:

  • #include <sys/types.h>
  • #include <sys/ipc.h>
  • #include <sys/msg.h>

Syntax: int msgget(key_t key, int msgflg);

RETURN VALUE: If successful, the return value will be the message queue identifier (a nonnegative integer), otherwise -1 with errno indicating the error.

ERRORS: On failure, errno is set to one of the following values which are given below:

  • EACCES: A message queue exists for key, but the calling process does not have  permission  to  access  the  queue,  and does not have the CAP_IPC_OWNER capability.
  • EEXIST: A message  queue  exists  for  key  and  msgflg  specified  both IPC_CREAT and IPC_EXCL.
  • ENOENT: No  message  queue  exists  for  key  and msgflg did not specify IPC_CREAT.
  • ENOMEM: A message queue has to be created but the system does  not  have enough memory for the new data structure.
  • ENOSPC: A  message  queue has to be created but the system limit for the maximum number of message queues (MSGMNI) would be exceeded.
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