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)

SHMAT(2)						      BSD System Calls Manual							  SHMAT(2)

NAME

     shmat, shmdt -- map/unmap shared memory

SYNOPSIS

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

     void *
     shmat(int shmid, void *shmaddr, int shmflg);

     int
     shmdt(void *shmaddr);

DESCRIPTION

     shmat() maps the shared memory segment associated with the shared memory identifier shmid into the address space of the calling process. The
     address at which the segment is mapped is determined by the shmaddr parameter. If it is equal to 0, the system will pick an address itself.
     Otherwise, an attempt is made to map the shared memory segment at the address shmaddr specifies. If SHM_RND is set in shmflg, the system will
     round the address down to a multiple of SHMLBA bytes (SHMLBA is defined in <sys/shm.h> ).	A shared memory segment can be mapped read-only by
     specifying the SHM_RDONLY flag in shmflg.	shmdt() unmaps the shared memory segment that is currently mapped at shmaddr from the calling
     process' address space.  shmaddr must be a value returned by a prior shmat() call. A shared memory segment will remain existant until it is
     removed by a call to shmctl(2) with the IPC_RMID command.

RETURN VALUES

     shmat() returns the address at which the shared memory segment has been mapped into the calling process' address space when successful,
     shmdt() returns 0 on successful completion. Otherwise, a value of -1 is returned, and the global variable errno is set to indicate the error.

ERRORS

     shmat() will fail if:

     [EACCES]		The calling process has no permission to access this shared memory segment.

     [ENOMEM]		There is not enough available data space for the calling process to map the shared memory segment.

     [EINVAL]		shmid is not a valid shared memory identifier.	shmaddr specifies an illegal address.

     [EMFILE]		The number of shared memory segments has reached the system-wide limit.
     shmdt() will fail if:

     [EINVAL]		shmaddr is not the start address of a mapped shared memory segment.

SEE ALSO

     shmctl(2), shmget(2), mmap(2)

BSD
								  August 17, 1995							       BSD