What are message queues explain with an example?
A message queue can be created by one process and used by multiple processes that read and/or write messages to the queue. For example, a server process can read and write messages from and to a message queue created for client processes.
Which of the following function is used to get the information about created message queue?
msgget(): either returns the message queue identifier for a newly created message queue or returns the identifiers for a queue which exists with the same key value. msgsnd(): Data is placed on to a message queue by calling msgsnd(). msgrcv(): messages are retrieved from a queue.
Where are message queues stored in Linux?
Edit: I read this in the book The Linux Programming Interface : On Linux, POSIX message queues are implemented as i-nodes in a virtual file system, and message queue descriptors and open message queue descriptions are implemented as file descriptors and open file descriptions, respectively.
What is message queue in operating system?
A message queue is an interprocess communication (IPC) mechanism that allows independent but cooperating tasks (that is, active classes) within a single CPU to communicate with one another. An active class is considered a task in Rhapsody®.
How do I open a message queue in Linux?
Message queues are created and opened using mq_open(3); this function returns a message queue descriptor (mqd_t), which is used to refer to the open message queue in later calls.
What is the use of @msgctl?
msgctl () performs the control operation specified by cmd on the System V message queue with identifier msqid .
How do I use msgctl () to avoid grief?
By using msgctl () with a selective set of commands, you have the ability to manipulate those items which are less likely to cause grief. Let’s look at these commands: Retrieves the msqid_ds structure for a queue, and stores it in the address of the buf argument.
Which privilege is required to raise MSG_qbytes beyond msgmnb?
Appropriate privilege (Linux: the CAP_SYS_RESOURCE capability) is required to raise the msg_qbytes value beyond the system parameter MSGMNB . IPC_RMID Immediately remove the message queue, awakening all waiting reader and writer processes (with an error return and errno set to EIDRM ).
Which members of the MSG_qbytes structure are updated?
The following members of the structure are updated: msg_qbytes, msg_perm.uid, msg_perm.gid, and (the least significant 9 bits of) msg_perm.mode . The effective UID of the calling process must match the owner ( msg_perm.uid) or creator ( msg_perm.cuid) of the message queue, or the caller must be privileged.