add rudimentary locking capability to Friendica functions

1 files changed, 76 insertions, 0 deletions

diff --git a/include/lock.php b/include/lock.php
new file mode 100644
index 000000000..be6130e1d
--- /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;
+}}