judge: be more graceful around worker timeouts

- Increase the timeout to 60s to avoid killing the worker when a user has
  aborted a long-running compilation.
- Rather than display `EOFError` when we kill the worker, display a more
  informative `TimeoutError` instead.

Author: Xyene

dmoj/judge.py

@@ -46,7 +46,10 @@ class IPC(Enum):
     REQUEST_ABORT = 'REQUEST-ABORT'
 
 
-IPC_TEARDOWN_TIMEOUT = 5  # seconds
+# This needs to be at least as large as the timeout for the largest compiler time limit, but we don't enforce that here.
+# (Otherwise, aborting during a compilation that exceeds this time limit would result in a `TimeoutError` IE instead of
+# a `CompileError`.)
+IPC_TIMEOUT = 60  # seconds
 
 
 logger = logging.getLogger(__name__)
@@ -302,6 +305,7 @@ class JudgeWorker:
     def __init__(self, submission: Submission) -> None:
         self.submission = submission
         self._abort_requested = False
+        self._sent_sigkill_to_worker_process = False
         # FIXME(tbrindus): marked Any pending grader cleanups.
         self.grader: Any = None
 
@@ -326,6 +330,10 @@ def communicate(self) -> Generator[Tuple[IPC, tuple], None, None]:
                 logger.error('Worker has not sent a message in %d seconds, assuming dead and killing.', recv_timeout)
                 self.worker_process.kill()
                 raise
+            except EOFError:
+                if self._sent_sigkill_to_worker_process:
+                    raise TimeoutError('worker did not exit in %d seconds, so it was killed' % IPC_TIMEOUT)
+                raise
             except Exception:
                 logger.error('Failed to read IPC message from worker!')
                 raise
@@ -336,16 +344,17 @@ def communicate(self) -> Generator[Tuple[IPC, tuple], None, None]:
             else:
                 yield ipc_type, data
 
-    def wait_with_timeout(self, timeout=IPC_TEARDOWN_TIMEOUT) -> None:
+    def wait_with_timeout(self) -> None:
         if self.worker_process and self.worker_process.is_alive():
             # Might be None if run was never called, or failed.
             try:
-                self.worker_process.join(timeout=timeout)
+                self.worker_process.join(timeout=IPC_TIMEOUT)
             except OSError:
                 logger.exception('Exception while waiting for worker to shut down, ignoring...')
             finally:
                 if self.worker_process.is_alive():
                     logger.error('Worker is still alive, sending SIGKILL!')
+                    self._sent_sigkill_to_worker_process = True
                     self.worker_process.kill()
 
     def request_abort_grading(self) -> None:
@@ -426,7 +435,7 @@ def _report_unhandled_exception() -> None:
                 # We may have failed before sending the IPC.BYE down the connection, in which case the judge will never
                 # close its side of the connection -- so `ipc_recv_thread` will never exit. But we can't wait forever in
                 # this case, since we're blocking the main judge from proceeding.
-                ipc_recv_thread.join(timeout=IPC_TEARDOWN_TIMEOUT)
+                ipc_recv_thread.join(timeout=IPC_TIMEOUT)
                 if ipc_recv_thread.is_alive():
                     logger.error('Judge IPC recv thread is still alive after timeout, shutting worker down anyway!')