Update _at_fork_reinit impl

srikanthccv · srikanthccv · commit b07758fb9491 · 2021-10-31T17:27:47.000+05:30
diff --git a/opentelemetry-sdk/src/opentelemetry/sdk/trace/export/__init__.py b/opentelemetry-sdk/src/opentelemetry/sdk/trace/export/__init__.py
@@ -17,8 +17,9 @@
 import sys
 import threading
 import typing
+import os
 from enum import Enum
-from os import environ, linesep, register_at_fork
+from os import environ, linesep
 from typing import Optional
 
 from opentelemetry.context import (
@@ -197,7 +198,9 @@ def __init__(
             None
         ] * self.max_export_batch_size  # type: typing.List[typing.Optional[Span]]
         self.worker_thread.start()
-        register_at_fork(after_in_child=self._at_fork_reinit)
+        # Only available in *nix since py37.
+        if hasattr(os, "register_at_fork"):
+            os.register_at_fork(after_in_child=self._at_fork_reinit)
 
     def on_start(
         self, span: Span, parent_context: typing.Optional[Context] = None
@@ -222,12 +225,23 @@ def on_end(self, span: ReadableSpan) -> None:
                 self.condition.notify()
 
     def _at_fork_reinit(self):
-        self.condition._at_fork_reinit()
+        # worker_thread is local to a process, only the thread that issued fork continues
+        # to exist. A new worker thread must be started in child process.
         self.worker_thread = threading.Thread(
             name="OtelBatchSpanProcessor", target=self.worker, daemon=True
         )
         self.worker_thread.start()
 
+        # could be in an inconsistent state after fork, reinitialise by calling `_at_fork_reinit`
+        # (creates a new lock internally https://github.com/python/cpython/blob/main/Python/thread_pthread.h#L727)
+        # if exists, otherwise create a new one.
+        if hasattr(self.condition, "_at_fork_reinit"):
+            self.condition._at_fork_reinit()
+        else:
+            self.condition = threading.Condition(threading.Lock())
+
+        self.queue.clear()
+
     def worker(self):
         timeout = self.schedule_delay_millis / 1e3
         flush_request = None  # type: typing.Optional[_FlushRequest]
