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Merge pull request #375 from fermionic/diaspora-prevent-fcontact-race-conditions

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add some timeouts to prevent deadlock
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friendica 2012-07-05 18:05:32 -07:00
commit 09959b1b1c
2 changed files with 18 additions and 9 deletions
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12
include/diaspora.php
View file

@ -119,6 +119,9 @@ function find_diaspora_person_by_handle($handle) {
$update = false; $update = false;
$got_lock = false; $got_lock = false;
$endlessloop = 0;
$maxloops = 10;
do { do {
$r = q("select * from fcontact where network = '%s' and addr = '%s' limit 1", $r = q("select * from fcontact where network = '%s' and addr = '%s' limit 1",
dbesc(NETWORK_DIASPORA), dbesc(NETWORK_DIASPORA),
@ -153,7 +156,12 @@ function find_diaspora_person_by_handle($handle) {
// Lock the function to prevent race conditions if multiple items // Lock the function to prevent race conditions if multiple items
// come in at the same time from a person who doesn't exist in // come in at the same time from a person who doesn't exist in
// fcontact // fcontact
$got_lock = lock_function('find_diaspora_person_by_handle', false); //
// Don't loop forever. On the last loop, try to create the contact
// whether the function is locked or not. Maybe the locking thread
// has died or something. At any rate, a duplicate in 'fcontact'
// is a much smaller problem than a deadlocked thread
$got_lock = (($endlessloop + 1) < $maxloops ? lock_function('find_diaspora_person_by_handle', false) : true );
if($got_lock) { if($got_lock) {
logger('find_diaspora_person_by_handle: create or refresh', LOGGER_DEBUG); logger('find_diaspora_person_by_handle: create or refresh', LOGGER_DEBUG);
@ -175,7 +183,7 @@ function find_diaspora_person_by_handle($handle) {
block_on_function_lock('find_diaspora_person_by_handle'); block_on_function_lock('find_diaspora_person_by_handle');
} }
} }
} while((! $person) && (! $got_lock)); } while((! $person) && (! $got_lock) && (++$endlessloop < $maxloops));
// We need to try again if the person wasn't in 'fcontact' but the function was locked. // We need to try again if the person wasn't in 'fcontact' but the function was locked.
// The fact that the function was locked may mean that another process was creating the // The fact that the function was locked may mean that another process was creating the
// person's record. It could also mean another process was creating or updating an unrelated // person's record. It could also mean another process was creating or updating an unrelated

15
include/lock.php
View file

@ -3,11 +3,12 @@
// Provide some ability to lock a PHP function so that multiple processes // Provide some ability to lock a PHP function so that multiple processes
// can't run the function concurrently // can't run the function concurrently
if(! function_exists('lock_function')) { if(! function_exists('lock_function')) {
function lock_function($fn_name, $block = true, $wait_sec = 2) { function lock_function($fn_name, $block = true, $wait_sec = 2, $timeout = 30) {
if( $wait_sec == 0 ) if( $wait_sec == 0 )
$wait_sec = 2; // don't let the user pick a value that's likely to crash the system $wait_sec = 2; // don't let the user pick a value that's likely to crash the system
$got_lock = false; $got_lock = false;
$start = time();
do { do {
q("LOCK TABLE locks WRITE"); q("LOCK TABLE locks WRITE");
@ -33,19 +34,21 @@ function lock_function($fn_name, $block = true, $wait_sec = 2) {
if(($block) && (! $got_lock)) if(($block) && (! $got_lock))
sleep($wait_sec); sleep($wait_sec);
} while(($block) && (! $got_lock)); } while(($block) && (! $got_lock) && ((time() - $start) < $timeout));
logger('lock_function: function ' . $fn_name . ' with blocking = ' . $block . ' got_lock = ' . $got_lock, LOGGER_DEBUG); logger('lock_function: function ' . $fn_name . ' with blocking = ' . $block . ' got_lock = ' . $got_lock . ' time = ' . (time() - $start), LOGGER_DEBUG);
return $got_lock; return $got_lock;
}} }}
if(! function_exists('block_on_function_lock')) { if(! function_exists('block_on_function_lock')) {
function block_on_function_lock($fn_name, $wait_sec = 2) { function block_on_function_lock($fn_name, $wait_sec = 2, $timeout = 30) {
if( $wait_sec == 0 ) if( $wait_sec == 0 )
$wait_sec = 2; // don't let the user pick a value that's likely to crash the system $wait_sec = 2; // don't let the user pick a value that's likely to crash the system
$start = time();
do { do {
$r = q("SELECT locked FROM locks WHERE name = '%s' LIMIT 1", $r = q("SELECT locked FROM locks WHERE name = '%s' LIMIT 1",
dbesc($fn_name) dbesc($fn_name)
@ -54,7 +57,7 @@ function block_on_function_lock($fn_name, $wait_sec = 2) {
if(count($r) && $r[0]['locked']) if(count($r) && $r[0]['locked'])
sleep($wait_sec); sleep($wait_sec);
} while(count($r) && $r[0]['locked']); } while(count($r) && $r[0]['locked'] && ((time() - $start) < $timeout));
return; return;
}} }}
@ -62,11 +65,9 @@ function block_on_function_lock($fn_name, $wait_sec = 2) {
if(! function_exists('unlock_function')) { if(! function_exists('unlock_function')) {
function unlock_function($fn_name) { function unlock_function($fn_name) {
//$r = q("LOCK TABLE lock WRITE");
$r = q("UPDATE locks SET locked = 0 WHERE name = '%s' LIMIT 1", $r = q("UPDATE locks SET locked = 0 WHERE name = '%s' LIMIT 1",
dbesc($fn_name) dbesc($fn_name)
); );
//$r = q("UNLOCK TABLES");
logger('unlock_function: released lock for function ' . $fn_name, LOGGER_DEBUG); logger('unlock_function: released lock for function ' . $fn_name, LOGGER_DEBUG);