shmop_open()

(PHP 4 >= 4.0.4, PHP 5, PHP 7)

Create or open shared memory block

说明

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

参数

$key

System's id for the shared memory block. Can be passed as a decimal or hex.

The flags that you can use:

• "a" for access(sets SHM_RDONLY for shmat)use this flag when you need to open an existing shared memory segment for read only
• "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
• "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.
• "n" create a new memory segment(sets IPC_CREATE|IPC_EXCL)use this flag when you want to create a new shared memory segment but if one already exists with the same flag, fail. This is useful for security purposes, using this you can prevent race condition exploits.

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 example0644

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

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

返回值

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

更新日志

范例

Create a new shared memory block

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

参见

• shmop_close()Close shared memory block
• shmop_delete()Delete shared memory block

On *nix systems shmop_open is able to create an "infinite" amount of segments when setting $key = 0.
After executing the following command twice in an interactive shell
php > $res = shmop_open(0,"n",0600,1024);
list the memory segments currently present 
$ ipcs -m
------ Shared Memory Segments --------
key    shmid   owner   perms   bytes   nattch   status
0x00000000 2293762  user    600    1024    0
0x00000000 2326531  user    600    1024    0
For any integer  0 in conjunction with the flag "n" shmop_open works like documented. It fails.

There is a little ftok function. This function isn't included into php for windows so i've grabbed it directly from linux glibc 2.3.2 source code. I hope that this can be useful.
There is the code:

sorry for my english :)

I'm having the same issue affecting XP and described below, on Mac OS X Lion.
To solve it, use before 'a' flag, then 'n'. Avoid 'c' flag.

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