php man page for shmop_open

SHMOP_OPEN(3)								 1							     SHMOP_OPEN(3)

shmop_open - Create or open shared memory block

SYNOPSIS
       int shmop_open (int  $key, string  $flags, int  $mode, int  $size)

DESCRIPTION
       shmop_open(3) can create or open a shared memory block.

PARAMETERS
	      o $key
		- System's id for the shared memory block. Can be passed as a decimal or hex.

	      o $flags
		- The flags that you can use:

		     o	"a"  for access (sets SHM_RDONLY for shmat) use this flag when you need to open an existing shared memory segment for read
		     only

		     o "c" for create (sets IPC_CREATE) use this flag when you need to create a new shared memory segment or if a segment with the
		     same key exists, try to open it for read and write

		     o "w" for read & write access use this flag when you need to read and write to a shared memory segment, use this flag in most
		     cases.

		     o "n" create a new memory segment (sets IPC_CREATE|IPC_EXCL) use this flag when you want to create a new shared  memory  seg-
		     ment  but	if  one  already exists with the same flag, fail. This is useful for security purposes, using this you can prevent
		     race condition exploits.

	      o $mode
		- 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, like for example 0644

	      o $size
		- The size of the shared memory block you wish to create in bytes

       Note

	       Note: the 3rd and 4th should be entered as 0 if you are opening an existing memory segment.

RETURN VALUES
	On  success  shmop_open(3)  will  return  an id that you can use to access the shared memory segment you've created.  FALSE is returned on
       failure.

EXAMPLES
       Example #1

	      Create a new shared memory block

	      <?php
	      $shm_key = ftok(__FILE__, 't');
	      $shm_id = shmop_open($shm_key, "c", 0644, 100);
	      ?>

	This example opened a shared memory block with a system id returned by ftok(3).

SEE ALSO
       shmop_close(3), shmop_delete(3).

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