Some database improvements and associated changes in webgui

webgui/lib/db.inc

@@ -8,3 +8,50 @@
 
 */
 
+function db_lock_acquire($table, $key, $userid) {
+    global $pdo;
+    $token = bin2hex(random_bytes(8));
+    // first try new lock
+    $sql = "INSERT INTO recordlock (lock_table, lock_key, token, userid) "
+         . "VALUES (?, ?, ?, ?)";
+    try {
+        $sth = $pdo->prepare($sql);
+        $sth->execute([$table, $key, $token, $userid]);
+        return $token;
+    } catch (PDOException $e) {
+        if ($e->errorInfo[1] != 1062) {
+            throw $e;
+        }
+    }
+    // lazy locking: lock exists but is old, so we use it
+    $sql = "UPDATE recordlock "
+         . "SET token=?, userid=?, "
+         . "created_at=CURRENT_TIMESTAMP, last_seen=CURRENT_TIMESTAMP "
+         . "WHERE lock_table=? AND lock_key=? "
+         . "AND last_seen<CURRENT_TIMESTAMP-INTERVAL 5 MINUTE";
+    $sth = $pdo->prepare($sql);
+    $sth->execute([$token, $userid, $table, $key]);
+    if ($stmt->rowCount() === 1) {
+        return $token;
+    }
+    return null;
+}
+
+function db_lock_refresh($token) {
+    global $pdo;
+    $sql = "UPDATE recordlock "
+         . "SET last_seen=CURRENT_TIMESTAMP "
+         . "WHERE token=?";
+    $sth = $pdo->prepare($sql);
+    $sth->execute([$token]);
+    return $sth->rowCount() === 1;
+}
+
+
+function db_lock_release($token) {
+    global $pdo;
+    $sql = "DELETE FROM recordlock WHERE token=?";
+    $sth = $pdo->prepare($sql);
+    $sth->execute([$token]);
+    return $sth->rowCount() === 1;
+}