add rudimentary locking capability to Friendica functions

3 files changed, 154 insertions, 21 deletions

diff --git a/include/Scrape.php b/include/Scrape.php
index 4f53effe9..b784650cd 100644
--- 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 5ab0ee674..29846eedf 100755
--- 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
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;
+}}