shmdt Subroutine

Purpose

Detaches a shared memory segment.

Library

Standard C Library (libc.a)

Syntax

#include <sys/shm.h>

Description

The shmdt subroutine detaches from the data segment of the calling process the shared memory segment located at the address specified by the SharedMemoryAddress parameter.

Mapped file segments are automatically detached when the mapped file is closed. However, you can use the shmdt subroutine to explicitly release the segment register used to map a file. Shared memory segments must be explicitly detached with the shmdt subroutine.

If the file was mapped for writing, the shmdt subroutine updates the mtime and ctime time stamps.

The following limits apply to shared memory:

• Maximum shared-memory segment size is:
  • 256M bytes before AIX® 4.3.1
  • 2G bytes for AIX 4.3.1 through AIX 5.1
  • 64G bytes for 64-bit applications for AIX 5.1 and later
• Minimum shared-memory segment size is 1 byte.
• Maximum number of shared memory IDs is 4096 for operating system releases before AIX 4.3.2 and 131072 for AIX 4.3.2 and following.

Parameters

Return Values

When successful, the shmdt subroutine returns a value of 0. Otherwise, the shared memory segment at the address specified by the SharedMemoryAddress parameter is not detached, a value of -1 is returned, and the errno global variable is set to indicate the error.

Error Codes

The shmdt subroutine is unsuccessful if the following condition is true: