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Create or open shared memory block
(PHP 4 >= 4.0.4, PHP 5)
Example 2233. Create a new shared memory block<?phpCode Examples / Notes » shmop_opencraig manley
To: macmaster at pobox dot com: To clear up some new confusion: you said the shm key is 8 bytes long. As far as I know it's 4 bytes (32bits). Check out the output of ipcs on Linux below to see what I mean. ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x6e6a694d 65538 mijnbel 644 65536 0 0x326e794d 98307 mijnbel 644 65536 0 0x62417347 131076 smsklap 644 65536 0 mitchell_shnier
To check whether a particular shared memory segment is already created, you need to concatenate the "a" and "c" flags. For example (where $SystemKey is the Unix key used by the other process(es) with which you want to share this memory segment)... $shm_id = shmop_open($SystemKey, "ac", 0, 0); if ($shm_id) { #it is already created } else { #you need to create it with shmop_open using "c" only } Using only "a" does not work (just as using only IPC_EXCL in the Unix shmget() call is meaningless). Also, use the ipcs shell command to see your shared memory segments. daniele_dll
There is a little ftok function. This function isn't included into php for windows so i've grabbed it directly from linux glibc 2.3.2 source code. I hope that this can be useful. There is the code: <?php function ftok($pathname, $proj_id) { $st = @stat($pathname); if (!$st) { return -1; } $key = sprintf("%u", (($st['ino'] & 0xffff) | (($st['dev'] & 0xff) << 16) | (($proj_id & 0xff) << 24))); return $key; } echo ftok($_SERVER["SCRIPT_FILENAME"], 250); ?> sorry for my english :) macmaster
the key is a LONG variable type, meaning that the key can only be eight (8) bytes long, which can be too short if you're using any form of automagic key generation (like a parsed filename)
me
Just an alternative idea if 'shared memory' is what you need for your websites, you can use tmpfs (on Linux): Get root to do this: mkdir /home/myname/tmpfs chown myname:mygroup /home/myname/tmpfs ..and this in a script executed at boot time: mount -t tmpfs /mnt/tmpfs /home/myuser/tmpfs Now you can use regular file functions (including locking) to access shared memory between all your processes. More info: http://docsun.cites.uiuc.edu/sun_docs/C/ ...and this because the note editor doesn't accept long lines... solaris_9/SUNWaadm/SYSADV1/p150.html chris petersen
Be warned that if you try to shmop_open with a key set to zero, shmop_open will seemingly work, and you can write to it, but you will not be able to read from it or delete it. If you're not careful, you can continue doing this - creating more and more shared memory blocks at "zero" until eventually you WILL start getting errors saying that php can't access or create the shared memory block, and you will have to restart your machine to free up all of those "zero" blocks.
hackie
All of the problems have been addressed in the CVS, in addition the a mode now indeed DOES attach to the segment in readonly mode (i.e. SHM_RDONLY), so using shm_write on it would fail with a warning. It has 2 new flags w (read/write) and n (new segment IPC_CREAT|IPC_EXCL). And a number of segfaults fixed :) |
