Description:
------------
hi,

think it would be a good idea to have some kind of atomic functions in php
otherwise having any kind of shared memory is pointless imo

so the patch adds a shmop-cas function

current version is gcc specific
i could also provide an x86 asm version (in gcc syntax)
that should at least be adaptable to other compilers

tested and working on 32bit linux, php built using gcc 4.5.2


bj

Test script:
---------------
if ($shm = shmop_open(0, 'c', 0640, 4096))
{
        $val1 = rand();
        $val2 = rand();
        echo("random values: $val1, $val2\n");

        $wr = shmop_write($shm, pack('V', $val1), 0);
        echo("$wr bytes written\n");

        $ov = shmop_cas($shm, 0, 0, $val2);
        echo("old val = $ov, should be $val1\n");

        $tv = shmop_cas($shm, 0, $ov, $val2);
        echo("temp = $tv, should still be $val1\n");

        $cv = shmop_cas($shm, 0, $ov, $val1);
        echo("current val = $cv, should be $val2\n");

        $rstr = shmop_read($shm, 0, 4);
        $rarr = unpack("Vval", $rstr);
        $rval = $rarr['val'];
        echo("value read: $rval, should still be $val2\n");

        if (! shmop_delete($shm))
                echo("delete shm failed\n");
        shmop_close($shm);
}