Split the convoluted "flush_buffers" into three scheduled tasks

flush_buffers: syncs oldest cache entry (period: 1s)
clean_cache: evicts old cache entries (period: 60s)
scavenge_dead_tasks: (period: 60s).

This PR should also fix the deadlock official-stockfish#2041.

server/fishtest/rundb.py

@@ -84,6 +84,8 @@ def schedule_tasks(self):
         if self.scheduler is None:
             self.scheduler = Scheduler(jitter=0.05)
         self.scheduler.add_task(1.0, self.flush_buffers)
+        self.scheduler.add_task(60.0, self.clean_cache)
+        self.scheduler.add_task(60.0, self.scavenge_dead_tasks)
         self.scheduler.add_task(180.0, self.validate_random_run)
 
     def validate_random_run(self):
@@ -477,70 +479,68 @@ def flush_all(self):
         print("done", flush=True)
 
     # For documentation of the cache format see "cache_schema" in schemas.py.
+
     def flush_buffers(self):
-        try:
-            self.run_cache_lock.acquire()
-            now = time.time()
-            old = now + 1
-            oldest_entry = None
-            # We make this a list to be able to change run_cache during iteration
-            for r_id, cache_entry in list(self.run_cache.items()):
+        oldest_entry = None
+        old = float("inf")
+        with self.run_cache_lock:
+            for cache_entry in self.run_cache.values():
                 run = cache_entry["run"]
-                if not cache_entry["is_changed"]:
-                    if not run["finished"] and (
-                        "last_scavenge_time" not in cache_entry
-                        or cache_entry["last_scavenge_time"] < now - 60
-                    ):
-                        cache_entry["last_scavenge_time"] = now
-                        if self.scavenge(run):
-                            with self.run_cache_write_lock:
-                                self.runs.replace_one({"_id": run["_id"]}, run)
-                    # Presently run["finished"] implies run["cores"]==0 but
-                    # this was not always true in the past.
-                    if (run["cores"] <= 0 or run["finished"]) and cache_entry[
-                        "last_access_time"
-                    ] < now - 300:
-                        del self.run_cache[r_id]
-                elif cache_entry["last_sync_time"] < old:
+                if cache_entry["is_changed"] and cache_entry["last_sync_time"] < old:
                     old = cache_entry["last_sync_time"]
                     oldest_entry = cache_entry
             if oldest_entry is not None:
                 oldest_run = oldest_entry["run"]
-                self.scavenge(oldest_run)
-                oldest_entry["last_scavenge_time"] = now
                 oldest_entry["is_changed"] = False
                 oldest_entry["last_sync_time"] = time.time()
                 with self.run_cache_write_lock:
                     self.runs.replace_one({"_id": oldest_run["_id"]}, oldest_run)
-        except Exception as e:
-            print(f"Flush exception: {str(e)}", flush=True)
-        finally:
-            self.run_cache_lock.release()
-
-    def scavenge(self, run):
-        if datetime.now(timezone.utc) < boot_time + timedelta(seconds=300):
-            return False
-        dead_task = False
-        old = datetime.now(timezone.utc) - timedelta(minutes=6)
-        task_id = -1
-        for task in run["tasks"]:
-            task_id += 1
-            if task["active"] and task["last_updated"] < old:
-                self.set_inactive_task(task_id, run)
-                dead_task = True
-                print(
-                    "dead task: run: https://tests.stockfishchess.org/tests/view/{} task_id: {} worker: {}".format(
-                        run["_id"], task_id, worker_name(task["worker_info"])
-                    ),
-                    flush=True,
-                )
-                self.handle_crash_or_time(run, task_id)
-                self.actiondb.dead_task(
-                    username=task["worker_info"]["username"],
-                    run=run,
-                    task_id=task_id,
-                )
-        return dead_task
+
+    def clean_cache(self):
+        now = time.time()
+        with self.run_cache_lock:
+            # We make this a list to be able to change run_cache during iteration
+            for r_id, cache_entry in list(self.run_cache.items()):
+                run = cache_entry["run"]
+                # Presently run["finished"] implies run["cores"]==0 but
+                # this was not always true in the past.
+                if (
+                    not cache_entry["is_changed"]
+                    and (run["cores"] <= 0 or run["finished"])
+                    and cache_entry["last_access_time"] < now - 300
+                ):
+                    del self.run_cache[r_id]
+
+    def scavenge_dead_tasks(self):
+        now = time.time()
+        dead_tasks = []
+        with self.run_cache_lock:
+            for cache_entry in self.run_cache.values():
+                run = cache_entry["run"]
+                if not cache_entry["is_changed"] and not run["finished"]:
+                    for task_id, task in enumerate(run["tasks"]):
+                        if (
+                            task["active"]
+                            and task["last_updated"].timestamp() < now - 360
+                        ):
+                            cache_entry["is_changed"] = True
+                            dead_tasks.append((task_id, run))
+        # We release the lock to avoid deadlock
+        for task_id, run in dead_tasks:
+            task = run["tasks"][task_id]
+            print(
+                "dead task: run: https://tests.stockfishchess.org/tests/view/{} task_id: {} worker: {}".format(
+                    run["_id"], task_id, worker_name(task["worker_info"])
+                ),
+                flush=True,
+            )
+            self.handle_crash_or_time(run, task_id)
+            self.actiondb.dead_task(
+                username=task["worker_info"]["username"],
+                run=run,
+                task_id=task_id,
+            )
+            self.set_inactive_task(task_id, run)
 
     def get_unfinished_runs_id(self):
         with self.run_cache_write_lock: