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add rudimentary locking capability to Friendica functions

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This commit is contained in:
Zach Prezkuta 2012-06-14 20:58:25 -06:00
parent 360c35e438
commit 168ae40dd2
4 changed files with 166 additions and 21 deletions
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69
include/diaspora.php
View file

@ -5,6 +5,7 @@ require_once('include/items.php');
require_once('include/bb2diaspora.php');
require_once('include/contact_selectors.php');
require_once('include/queue_fn.php');
require_once('include/lock.php');
function diaspora_dispatch_public($msg) {
@ -113,27 +114,83 @@ function diaspora_get_contact_by_handle($uid,$handle) {
}
function find_diaspora_person_by_handle($handle) {
$person = false;
$update = false;
$got_lock = false;
do {
$r = q("select * from fcontact where network = '%s' and addr = '%s' limit 1",
dbesc(NETWORK_DIASPORA),
dbesc($handle)
);
if(count($r)) {
$person = $r[0];
logger('find_diaspora_person_by handle: in cache ' . print_r($r,true), LOGGER_DEBUG);
// update record occasionally so it doesn't get stale
$d = strtotime($r[0]['updated'] . ' +00:00');
if($d > strtotime('now - 14 days'))
return $r[0];
$d = strtotime($person['updated'] . ' +00:00');
if($d < strtotime('now - 14 days'))
$update = true;
}
logger('find_diaspora_person_by_handle: refresh',LOGGER_DEBUG);
// FETCHING PERSON INFORMATION FROM REMOTE SERVER
//
// If the person isn't in our 'fcontact' table, or if he/she is but
// his/her information hasn't been updated for more than 14 days, then
// we want to fetch the person's information from the remote server.
//
// Note that $person isn't changed by this block of code unless the
// person's information has been successfully fetched from the remote
// server. So if $person was 'false' to begin with (because he/she wasn't
// in the local cache), it'll stay false, and if $person held the local
// cache information to begin with, it'll keep that information. That way
// if there's a problem with the remote fetch, we can at least use our
// cached information--it's better than nothing.
if((! $person) || ($update)) {
// Lock the function to prevent race conditions if multiple items
// come in at the same time from a person who doesn't exist in
// fcontact
$got_lock = lock_function('find_diaspora_person_by_handle', false);
if($got_lock) {
logger('find_diaspora_person_by_handle: create or refresh', LOGGER_DEBUG);
require_once('include/Scrape.php');
$r = probe_url($handle, PROBE_DIASPORA);
// Note that Friendica contacts can return a "Diaspora person"
// if Diaspora connectivity is enabled on their server
if((count($r)) && ($r['network'] === NETWORK_DIASPORA)) {
add_fcontact($r,$update);
return ($r);
$person = ($r);
}
return false;
unlock_function('find_diaspora_person_by_handle');
}
else {
logger('find_diaspora_person_by_handle: couldn\'t lock function', LOGGER_DEBUG);
if(! $person)
block_on_function_lock('find_diaspora_person_by_handle');
}
}
} while((! $person) && (! $got_lock));
// 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
// person's record. It could also mean another process was creating or updating an unrelated
// person.
//
// At any rate, we need to keep trying until we've either got the person or had a chance to
// try to fetch his/her remote information. But we don't want to block on locking the
// function, because if the other process is creating the record, then when we acquire the lock
// we'll dive right into creating another, duplicate record. We DO want to at least wait
// until the lock is released, so we don't flood the database with requests.
//
// If the person was in the 'fcontact' table, don't try again. It's not worth the time, since
// we do have some information for the person
return $person;
}

76
include/lock.php Normal file
View file

@ -0,0 +1,76 @@
<?php
// Provide some ability to lock a PHP function so that multiple processes
// can't run the function concurrently
// The function must have a line inserted into the 'lock' table with the
// function's name in the 'name' field
if(! function_exists('lock_function')) {
function lock_function($fn_name, $block = true, $wait_sec = 2) {
if( $wait_sec == 0 )
$wait_sec = 2; // don't let the user pick a value that's likely to crash the system
$got_lock = false;
do {
q("LOCK TABLE lock WRITE");
$r = q("SELECT locked FROM lock WHERE name = '%s' LIMIT 1",
dbesc($fn_name)
);
if((count($r)) && (! $r[0]['locked'])) {
q("UPDATE lock SET locked = 1 WHERE name = '%s' LIMIT 1",
dbesc($fn_name)
);
$got_lock = true;
}
elseif(! $r) { // the Boolean value for count($r) should be equivalent to the Boolean value of $r
q("INSERT INTO lock ( name, locked ) VALUES ( '%s', 1 )",
dbesc($fn_name)
);
$got_lock = true;
}
q("UNLOCK TABLES");
if(($block) && (! $got_lock))
sleep($wait_sec);
} while(($block) && (! $got_lock));
logger('lock_function: function ' . $fn_name . ' with blocking = ' . $block . ' got_lock = ' . $got_lock, LOGGER_DEBUG);
return $got_lock;
}}
if(! function_exists('block_on_function_lock')) {
function block_on_function_lock($fn_name, $wait_sec = 2) {
if( $wait_sec == 0 )
$wait_sec = 2; // don't let the user pick a value that's likely to crash the system
do {
$r = q("SELECT locked FROM lock WHERE name = '%s' LIMIT 1",
dbesc(fn_name)
);
if(count($r) && $r[0]['locked'])
sleep($wait_sec);
} while(count($r) && $r[0]['locked']);
return;
}}
if(! function_exists('unlock_function')) {
function unlock_function(fn_name) {
//$r = q("LOCK TABLE lock WRITE");
$r = q("UPDATE lock SET locked = 0 WHERE name = '%s' LIMIT 1",
dbesc(fn_name)
);
//$r = q("UNLOCK TABLES");
logger('unlock_function: released lock for function ' . fn_name, LOGGER_DEBUG);
return;
}}

12
update.php
View file

@ -1307,3 +1307,15 @@ function update_1150() {
return UPDATE_SUCCESS;
}
function update_1151() {
$r = q("CREATE TABLE IF NOT EXISTS lock (
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY ,
name CHAR(128) NOT NULL ,
locked TINYINT(1) NOT NULL DEFAULT '0'
) ENGINE = MYISAM DEFAULT CHARSET=utf8 ");
if (!$r)
return UPDATE_FAILED;
return UPDATE_SUCCESS;
}