shmop_open(3) [php man page]

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).

PHP Documentation Group 													     SHMOP_OPEN(3)

SHMGET(2)						      BSD System Calls Manual							 SHMGET(2)

NAME

     shmget -- obtain a shared memory identifier

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <sys/types.h>
     #include <sys/ipc.h>
     #include <sys/shm.h>

     int
     shmget(key_t key, size_t size, int flag);

DESCRIPTION

     Based on the values of key and flag, shmget() returns the identifier of a newly created or previously existing shared memory segment.  The
     key is analogous to a filename: it provides a handle that names an IPC object.  There are three ways to specify a key:

     o	 IPC_PRIVATE may be specified, in which case a new IPC object will be created.

     o	 An integer constant may be specified.	If no IPC object corresponding to key is specified and the IPC_CREAT bit is set in flag, a new one
	 will be created.

     o	 The ftok(3) may be used to generate a key from a pathname.

     The mode of a newly created IPC object is determined by OR'ing the following constants into the flag argument:

     S_IRUSR	   Read access for owner.

     S_IWUSR	   Write access for owner.

     S_IRGRP	   Read access for group.

     S_IWGRP	   Write access for group.

     S_IROTH	   Read access for other.

     S_IWOTH	   Write access for other.

     When creating a new shared memory segment, size indicates the desired size of the new segment in bytes.  The size of the segment may be
     rounded up to a multiple convenient to the kernel (i.e., the page size).

RETURN VALUES

     Upon successful completion, shmget() returns the positive integer identifier of a shared memory segment.  Otherwise, -1 is returned and errno
     set to indicate the error.

ERRORS

     The shmget() system call will fail if:

     [EINVAL]		Size specified is greater than the size of the previously existing segment.  Size specified is less than the system
			imposed minimum, or greater than the system imposed maximum.

     [ENOENT]		No shared memory segment was found matching key, and IPC_CREAT was not specified.

     [ENOSPC]		The kernel was unable to allocate enough memory to satisfy the request.

     [EEXIST]		IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to key already exists.

SEE ALSO

     shmat(2), shmctl(2), shmdt(2), stat(2), ftok(3)

BSD
								 December 17, 2010							       BSD