shm_open

Description

shm_open() can create or open a shared memory block.

shm_open() takes 4 parameters: key, which is the system's id for the shared memory block, this parameter can be passed as a decimal or hex. The second parameter are the flags that you can use:

• "a" for access (sets IPC_EXCL) use this flag when you need to open an existing shared memory segment

• "c" for create (sets IPC_CREATE) use this flag when you need to create a new shared memory segment.

The third parameter is the mode, which are the permissions that you wish to assign to your memory segment, those are the same as permission for a file. Permissions need to be passed in octal form ex. 0644. The last parameter is size of the shared memory block you wish to create in bytes.

Example 1. Create a new shared memory block <?php $shm_id = shm_open(0x0fff, "c", 0644, 100); ?>

This example opened a shared memory block with a system id of 0x0fff.