Use shared locks for Fenrir instance coordination

src/fenrirscreenreader/commands/onHeartBeat/76000-time.py

@@ -5,6 +5,7 @@
 # By Chrys, Storm Dragon, and contributors.
 
 import datetime
+import fcntl
 import os
 import tempfile
 import time
@@ -34,55 +35,45 @@ class command:
     def _get_announcement_lock_path(self):
         return os.path.join(
             tempfile.gettempdir(),
-            f"fenrirscreenreader-{os.getuid()}-time-announcement.lock",
+            "fenrirscreenreader-time-announcement.lock",
         )
 
-    def _try_create_announcement_lock(self, announcement_slot, now):
-        lock_path = self._get_announcement_lock_path()
-        try:
-            lock_fd = os.open(lock_path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
-        except FileExistsError:
-            return False
-
-        with os.fdopen(lock_fd, "w", encoding="utf-8") as lock_file:
-            lock_file.write(f"{os.getpid()} {announcement_slot} {now}\n")
-        return True
-
-    def _read_announcement_lock_slot(self, lock_path):
-        with open(lock_path, "r", encoding="utf-8") as lock_file:
-            lock_content = lock_file.readline().strip().split()
+    def _read_announcement_lock_slot(self, lock_file):
+        lock_file.seek(0)
+        lock_content = lock_file.readline().strip().split()
         if len(lock_content) < 2:
             return ""
         return lock_content[1]
 
     def _claim_announcement_lock(self, announcement_slot):
         now = time.time()
-        if self._try_create_announcement_lock(announcement_slot, now):
-            return True
-
         lock_path = self._get_announcement_lock_path()
         try:
-            lock_slot = self._read_announcement_lock_slot(lock_path)
-            lock_stat = os.stat(lock_path)
-        except FileNotFoundError:
-            return self._try_create_announcement_lock(announcement_slot, now)
+            lock_fd = os.open(lock_path, os.O_CREAT | os.O_RDWR, 0o666)
         except OSError:
             return False
-
-        if lock_slot == announcement_slot:
-            return False
-
-        if not lock_slot and now - lock_stat.st_mtime < ANNOUNCEMENT_LOCK_TIMEOUT_SEC:
-            return False
-
         try:
-            os.unlink(lock_path)
-        except FileNotFoundError:
-            pass
+            os.chmod(lock_path, 0o666)
         except OSError:
-            return False
+            pass
 
-        return self._try_create_announcement_lock(announcement_slot, now)
+        with os.fdopen(lock_fd, "r+", encoding="utf-8") as lock_file:
+            try:
+                fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX)
+                lock_slot = self._read_announcement_lock_slot(lock_file)
+                lock_stat = os.fstat(lock_file.fileno())
+
+                if lock_slot == announcement_slot:
+                    return False
+
+                lock_file.seek(0)
+                lock_file.truncate()
+                lock_file.write(f"{os.getpid()} {announcement_slot} {now}\n")
+                lock_file.flush()
+                os.fsync(lock_file.fileno())
+                return True
+            finally:
+                fcntl.flock(lock_file.fileno(), fcntl.LOCK_UN)
 
     def run(self):
         if not self.env["runtime"]["SettingsManager"].get_setting_as_bool(

src/fenrirscreenreader/core/remoteManager.py

@@ -27,6 +27,7 @@ command interrupt
 
 
 import hashlib
+import fcntl
 import os
 import tempfile
 import time
@@ -38,7 +39,7 @@ from fenrirscreenreader.core.i18n import _
 
 
 REMOTE_COMMAND_LOCK_TIMEOUT_SEC = 2.0
-REMOTE_COMMAND_LOCK_PREFIX = f"fenrirscreenreader-{os.getuid()}-remote-"
+REMOTE_COMMAND_LOCK_PREFIX = "fenrirscreenreader-remote-"
 
 
 class RemoteManager:
@@ -304,47 +305,62 @@ class RemoteManager:
             except OSError:
                 pass
 
-    def _try_create_remote_command_lock(self, lock_path, now):
+    def _read_remote_command_lock(self, lock_file):
+        lock_file.seek(0)
+        lock_parts = lock_file.readline().strip().split()
         try:
-            lock_fd = os.open(lock_path, os.O_CREAT | os.O_EXCL | os.O_WRONLY, 0o600)
-        except FileExistsError:
-            return False
+            lock_pid = int(lock_parts[0]) if lock_parts else 0
+        except ValueError:
+            lock_pid = 0
+        return lock_pid
 
-        with os.fdopen(lock_fd, "w", encoding="utf-8") as lock_file:
-            lock_file.write(f"{os.getpid()} {now}\n")
-        return True
+    def _write_remote_command_lock(self, lock_file, now):
+        lock_file.seek(0)
+        lock_file.truncate()
+        lock_file.write(f"{os.getpid()} {now}\n")
+        lock_file.flush()
+        os.fsync(lock_file.fileno())
+
+    def _open_remote_command_lock(self, lock_path):
+        try:
+            lock_fd = os.open(lock_path, os.O_CREAT | os.O_RDWR, 0o666)
+        except OSError:
+            return None
+        try:
+            os.chmod(lock_path, 0o666)
+        except OSError:
+            pass
+
+        return os.fdopen(lock_fd, "r+", encoding="utf-8")
 
     def _claim_remote_command(self, event_data):
         lock_path = self._get_remote_command_lock_path(event_data)
         now = time.time()
         self._cleanup_stale_remote_command_locks(now)
-        if self._try_create_remote_command_lock(lock_path, now):
-            return True
-
-        try:
-            with open(lock_path, "r", encoding="utf-8") as lock_file:
-                lock_parts = lock_file.readline().strip().split()
-            lock_pid = int(lock_parts[0]) if lock_parts else 0
-            lock_stat = os.stat(lock_path)
-        except FileNotFoundError:
-            return self._try_create_remote_command_lock(lock_path, now)
-        except (OSError, ValueError):
+        lock_file = self._open_remote_command_lock(lock_path)
+        if lock_file is None:
             return False
 
-        if lock_pid == os.getpid():
-            return True
+        with lock_file:
+            try:
+                fcntl.flock(lock_file.fileno(), fcntl.LOCK_EX)
+                lock_pid = self._read_remote_command_lock(lock_file)
+                lock_stat = os.fstat(lock_file.fileno())
 
-        if now - lock_stat.st_mtime < REMOTE_COMMAND_LOCK_TIMEOUT_SEC:
-            return False
+                if lock_pid == os.getpid():
+                    return True
 
-        try:
-            os.unlink(lock_path)
-        except FileNotFoundError:
-            pass
-        except OSError:
-            return False
+                if not lock_pid:
+                    self._write_remote_command_lock(lock_file, now)
+                    return True
 
-        return self._try_create_remote_command_lock(lock_path, now)
+                if now - lock_stat.st_mtime < REMOTE_COMMAND_LOCK_TIMEOUT_SEC:
+                    return False
+
+                self._write_remote_command_lock(lock_file, now)
+                return True
+            finally:
+                fcntl.flock(lock_file.fileno(), fcntl.LOCK_UN)
 
     def list_instances(self):
         instances = remoteInstanceRegistry.list_instances()

src/fenrirscreenreader/fenrirVersion.py

@@ -4,5 +4,5 @@
 # Fenrir TTY screen reader
 # By Chrys, Storm Dragon, and contributors.
 
-version = "2026.05.07"
+version = "2026.05.08"
 code_name = "testing"