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Request #55846 (shmop,) compare-and-swap functionality
Submitted: 2011-10-04 16:10 UTC Modified: 2016-10-07 13:02 UTC
Avg. Score:4.0 ± 1.0
Reproduced:1 of 1 (100.0%)
Same Version:1 (100.0%)
Same OS:1 (100.0%)
From: brohreit at gmx dot net Assigned:
Status: Open Package: *Extensibility Functions
PHP Version: 5.3.8 OS: all
Private report: No CVE-ID: None
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From: brohreit at gmx dot net
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 [2011-10-04 16:10 UTC] brohreit at gmx dot net

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


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-cas (last revision 2011-10-04 16:11 UTC by brohreit at gmx dot net)

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 [2016-08-03 18:16 UTC] 14463068 at qq dot com
hi, the shmop_cas() is very important, really strongly suggest to patch to shmop extension.  

e.g.  We're building a Neon-Network using share-memory block, when currently access the memory block, we need a memory-CAS algorithm.  and this patch seems works for 32 bit system.   would please consider?
 [2016-10-07 13:02 UTC]
-Package: Unknown/Other Function +Package: *Extensibility Functions
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