Merge pull request chigwell#274 from RizgarOzan/fix/windows-holder-pid-offset

fix(singleton): let a refused process read the holder PID on Windows

Author: chigwell

telegram_mcp/singleton.py

@@ -50,6 +50,9 @@
     # slot. Shared holders then coexist, and neither kind overlaps an exclusive
     # one. Locking past the end of the file is allowed.
     _SHARED_SLOTS = 64
+    # Windows locks are mandatory, so the exclusive holder writes its PID past
+    # the locked bytes, where a refused contender can still read it.
+    _PID_OFFSET = 1 + _SHARED_SLOTS
 
     def _lock_range(fh: IO, start: int, length: int) -> bool:
         try:
@@ -76,6 +79,8 @@ def _unlock(fh: IO) -> None:
 else:
     import fcntl
 
+    _PID_OFFSET = 0
+
     def _try_lock(fh: IO, shared: bool = False) -> bool:
         try:
             mode = fcntl.LOCK_SH if shared else fcntl.LOCK_EX
@@ -168,11 +173,12 @@ def release(self) -> None:
     def holder_pid(self) -> Optional[int]:
         """PID left in the lock file by the current exclusive holder, if any.
 
-        Best effort: Windows refuses to read a locked byte range, and a shared
-        holder records nothing (there may be several).
+        Best effort: a shared holder records nothing (there may be several).
         """
         try:
-            text = self.path.read_text().strip()
+            with open(self.path, "rb") as fh:
+                fh.seek(_PID_OFFSET)
+                text = fh.read().decode("ascii", "replace").strip()
         except OSError:
             return None
         return int(text) if text.isdigit() else None
@@ -183,7 +189,7 @@ def _record_holder(self, shared: bool) -> None:
         self._clear_holder()
         if not shared:
             try:
-                self._fh.write(str(os.getpid()))
+                self._fh.write(" " * _PID_OFFSET + str(os.getpid()))
                 self._fh.flush()
             except OSError:
                 pass