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

add some timeouts to prevent deadlock

2 files changed, 18 insertions, 9 deletions

diff --git a/include/diaspora.php b/include/diaspora.php
index 29846eedf..35cd66059 100755
--- a/include/diaspora.php
+++ b/include/diaspora.php
@@ -119,6 +119,9 @@ function find_diaspora_person_by_handle($handle) {
 	$update = false;
 	$got_lock = false;
 
+	$endlessloop = 0;
+	$maxloops = 10;
+
 	do {
 		$r = q("select * from fcontact where network = '%s' and addr = '%s' limit 1",
 			dbesc(NETWORK_DIASPORA),
@@ -153,7 +156,12 @@ function find_diaspora_person_by_handle($handle) {
 			// 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);
+			//
+			// 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($got_lock) {
 				logger('find_diaspora_person_by_handle: create or refresh', LOGGER_DEBUG);
@@ -175,7 +183,7 @@ function find_diaspora_person_by_handle($handle) {
 					block_on_function_lock('find_diaspora_person_by_handle');
 			}
 		}
-	} while((! $person) && (! $got_lock));
+	} while((! $person) && (! $got_lock) && (++$endlessloop < $maxloops));
 	// We need to try again if the person wasn't in 'fcontact' but the function was locked.
 	// The fact that the function was locked may mean that another process was creating the
 	// person's record. It could also mean another process was creating or updating an unrelated
diff --git a/include/lock.php b/include/lock.php
index 9bdb71125..5f1ca6323 100644
--- a/include/lock.php
+++ b/include/lock.php
@@ -3,11 +3,12 @@
 // Provide some ability to lock a PHP function so that multiple processes
 // can't run the function concurrently
 if(! function_exists('lock_function')) {
-function lock_function($fn_name, $block = true, $wait_sec = 2) {
+function lock_function($fn_name, $block = true, $wait_sec = 2, $timeout = 30) {
 	if( $wait_sec == 0 )
 		$wait_sec = 2;	// don't let the user pick a value that's likely to crash the system
 
 	$got_lock = false;
+	$start = time();
 
 	do {
 		q("LOCK TABLE locks WRITE");
@@ -33,19 +34,21 @@ function lock_function($fn_name, $block = true, $wait_sec = 2) {
 		if(($block) && (! $got_lock))
 			sleep($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;
 }}
 
 
 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 )
 		$wait_sec = 2;	// don't let the user pick a value that's likely to crash the system
 
+	$start = time();
+
 	do {
 		$r = q("SELECT locked FROM locks WHERE name = '%s' LIMIT 1",
 				dbesc($fn_name)
@@ -54,7 +57,7 @@ function block_on_function_lock($fn_name, $wait_sec = 2) {
 		if(count($r) && $r[0]['locked'])
 			sleep($wait_sec);
 
-	} while(count($r) && $r[0]['locked']);
+	} while(count($r) && $r[0]['locked'] && ((time() - $start) < $timeout));
 
 	return;
 }}
@@ -62,11 +65,9 @@ function block_on_function_lock($fn_name, $wait_sec = 2) {
 
 if(! function_exists('unlock_function')) {
 function unlock_function($fn_name) {
-	//$r = q("LOCK TABLE lock WRITE");
 	$r = q("UPDATE locks SET locked = 0 WHERE name = '%s' LIMIT 1",
 			dbesc($fn_name)
 	     );
-	//$r = q("UNLOCK TABLES");
 
 	logger('unlock_function: released lock for function ' . $fn_name, LOGGER_DEBUG);