msgrcv

msgrcv is a system call in Unix-like operating systems that is used to receive messages from a message queue. It is part of the System V IPC (Inter-Process Communication) message queue facility. The primary purpose of msgrcv is to allow one process to retrieve messages that have been previously placed into a message queue by another process.

The msgrcv system call takes several arguments, including a message queue identifier, a pointer to a buffer where the received message will be stored, the maximum size of the buffer, a message type to filter messages, and a set of flags. The message type argument allows a receiving process to specify which types of messages it is interested in, enabling more selective retrieval. The flags can control aspects such as whether the call should block until a message is available or whether it should return immediately if no message is present.

When a process calls msgrcv, it attempts to read a message from the specified queue. If a matching message is found and the buffer is large enough, the message is copied into the buffer, and the call returns successfully. If no suitable message is available and the appropriate flags are set, the call may block, waiting for a message to arrive. If an error occurs, such as an invalid message queue identifier or insufficient permissions, the call will return an error code. msgrcv is a fundamental component for implementing inter-process communication patterns where data needs to be passed asynchronously between independent processes.