add rudimentary locking capability to Friendica functions

diff --git a/include/Scrape.php b/include/Scrape.php
index 4f53effe92b3653ea99a2688a2484736721af7bd..b784650cd168722cb462d4031e1a9fb888b9e7a8 100644 (file)
--- a/include/Scrape.php
+++ b/include/Scrape.php
@@ -432,7 +432,7 @@ function probe_url($url, $mode = PROBE_NORMAL) {
                                        intval(local_user())
                                );
                                if(count($x) && count($r)) {
-                                   $mailbox = construct_mailbox_name($r[0]);
+                                       $mailbox = construct_mailbox_name($r[0]);
                                        $password = '';
                                        openssl_private_decrypt(hex2bin($r[0]['pass']),$password,$x[0]['prvkey']);
                                        $mbox = email_connect($mailbox,$r[0]['user'],$password);

diff --git a/include/diaspora.php b/include/diaspora.php
index 5ab0ee6749d6fc775ae82a31eed8cc48a20cbd6a..29846eedf6918a609eb93ad5098a8170bee9300a 100755 (executable)
--- a/include/diaspora.php
+++ b/include/diaspora.php
@@ -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;
-       $r = q("select * from fcontact where network = '%s' and addr = '%s' limit 1",
-               dbesc(NETWORK_DIASPORA),
-               dbesc($handle)
-       );
-       if(count($r)) {
-               logger('find_diaspora_person_by handle: in cache ' . print_r($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];
-               $update = true;
-       }
-       logger('find_diaspora_person_by_handle: refresh',LOGGER_DEBUG);
-       require_once('include/Scrape.php');
-       $r = probe_url($handle, PROBE_DIASPORA);
-       if((count($r)) && ($r['network'] === NETWORK_DIASPORA)) {
-               add_fcontact($r,$update);
-               return ($r);
-       }
-       return 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
+                       $d = strtotime($person['updated'] . ' +00:00');
+                       if($d < strtotime('now - 14 days'))
+                               $update = true;
+               }
+
+
+               // 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);
+                                       $person = ($r);
+                               }
+
+                               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;
 }
 
 

diff --git a/include/lock.php b/include/lock.php
new file mode 100644 (file)
index 0000000..be6130e
--- /dev/null
+++ b/include/lock.php
@@ -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;
+}}

diff --git a/update.php b/update.php
index b8e247f57ce99f885714ce1467da93979ea0eb19..5e5ec3e865590812d57c0bd9e8a4b2cdcdd4910e 100644 (file)
--- a/update.php
+++ b/update.php
@@ -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;
+}
+