further enhanced error handling + added retries in case of parallel writes

db_init.php

@@ -140,18 +140,37 @@ function qdb_apply_migrations(PDO $pdo, string $schemaSql): bool {
     return $changed;
 }
 
-function qdb_acquire_lock() {
+/**
+ * Exclusive lock with short retries (non-blocking attempts). Avoids hung PHP workers
+ * when two writes overlap (app upload + website edit).
+ */
+function qdb_flock_exclusive_with_retry($lockFp, int $maxAttempts = 12, int $sleepMicros = 75000): void
+{
+    for ($attempt = 0; $attempt < $maxAttempts; $attempt++) {
+        if (flock($lockFp, LOCK_EX | LOCK_NB)) {
+            return;
+        }
+        if ($attempt < $maxAttempts - 1) {
+            usleep($sleepMicros);
+        }
+    }
+    throw new Exception('Could not acquire lock');
+}
+
+function qdb_open_writable_lock()
+{
     $lockFp = fopen(QDB_LOCK, 'c');
     if ($lockFp === false) {
         throw new Exception('Could not open lock file');
     }
-    if (!flock($lockFp, LOCK_EX)) {
-        fclose($lockFp);
-        throw new Exception('Could not acquire lock');
-    }
+    qdb_flock_exclusive_with_retry($lockFp);
     return $lockFp;
 }
 
+function qdb_acquire_lock() {
+    return qdb_open_writable_lock();
+}
+
 /**
  * Decrypt the master DB file into a temp SQLite file, or create a fresh one
  * from schema.sql if no DB exists yet.
@@ -171,12 +190,7 @@ function qdb_open(bool $writable = false): array {
 
     $lockFp = null;
     if ($writable) {
-        $lockFp = fopen(QDB_LOCK, 'c');
-        if ($lockFp === false) throw new Exception("Could not open lock file");
-        if (!flock($lockFp, LOCK_EX)) {
-            fclose($lockFp);
-            throw new Exception("Could not acquire lock");
-        }
+        $lockFp = qdb_open_writable_lock();
     }
 
     $tmpDb = tempnam(sys_get_temp_dir(), 'qdb_');
@@ -289,33 +303,26 @@ function qdb_discard(string $tmpDb, $lockFp): void {
  *
  * @return array{0: PDO, 1: string, 2: resource|null}|null
  */
-function qdb_open_read_or_fail(): ?array {
+/**
+ * @return array{0: PDO, 1: string, 2: resource|null}
+ */
+function qdb_open_read_or_fail(): array {
     try {
         return qdb_open(false);
     } catch (Throwable $e) {
-        if (function_exists('qdb_api_log_note_exception')) {
-            qdb_api_log_note_exception($e);
-        }
         require_once __DIR__ . '/lib/errors.php';
-        error_log('qdb_open_read: ' . $e->getMessage());
-        json_error('SERVER_ERROR', qdb_public_error_message($e, 'Database read'), 500);
+        qdb_emit_api_error($e, 'Database read');
     }
 }
 
 /**
- * Open a writable DB connection; on failure logs and returns a JSON error response.
- *
- * @return array{0: PDO, 1: string, 2: resource|null}|null
+ * @return array{0: PDO, 1: string, 2: resource|null}
  */
-function qdb_open_write_or_fail(): ?array {
+function qdb_open_write_or_fail(): array {
     try {
         return qdb_open(true);
     } catch (Throwable $e) {
-        if (function_exists('qdb_api_log_note_exception')) {
-            qdb_api_log_note_exception($e);
-        }
         require_once __DIR__ . '/lib/errors.php';
-        error_log('qdb_open_write: ' . $e->getMessage());
-        json_error('SERVER_ERROR', qdb_public_error_message($e, 'Database write'), 500);
+        qdb_emit_api_error($e, 'Database write');
     }
 }