Add "reinstall()" method to make it easier in spawn multiprocessing (#…

…1069)

loguru/_logger.py

@@ -1812,6 +1812,40 @@ def configure(self, *, handlers=None, levels=None, extra=None, patcher=None, act
 
         return [self.add(**params) for params in handlers]
 
+    def reinstall(self):
+        """Reinstall the core of logger.
+
+        When using multiprocessing, you can pass logger as a parameter to the target of
+        ``multiprocessing.Process``, and run this method once, thus you don't need to pass
+        logger to every function you called in the same process with spawn multiprocessing.
+
+        Examples
+        --------
+        >>> def subworker(logger):
+        ...     logger.reinstall()
+        ...     logger.info("Child")
+        ...     deeper_subworker()
+
+        >>> def deeper_subworker():
+        ...     logger.info("Grandchild")
+
+        >>> def test_process_spawn():
+        ...     spawn_context = multiprocessing.get_context("spawn")
+        ...     logger.add("file.log", context=spawn_context, enqueue=True, catch=False)
+        ...
+        ...     process = spawn_context.Process(target=subworker, args=(logger,))
+        ...     process.start()
+        ...     process.join()
+
+        ...     assert process.exitcode == 0
+
+        ...     logger.info("Main")
+        ...     logger.remove()
+        """
+        from loguru import logger
+
+        logger._core = self._core
+
     def _change_activation(self, name, status):
         if not (name is None or isinstance(name, str)):
             raise TypeError(

tests/test_reinstall.py

@@ -0,0 +1,72 @@
+import multiprocessing
+import os
+
+import pytest
+
+from loguru import logger
+
+
+@pytest.fixture
+def fork_context():
+    yield multiprocessing.get_context("fork")
+
+
+@pytest.fixture
+def spawn_context():
+    yield multiprocessing.get_context("spawn")
+
+
+class Writer:
+    def __init__(self):
+        self._output = ""
+
+    def write(self, message):
+        self._output += message
+
+    def read(self):
+        return self._output
+
+
+def subworker(logger):
+    logger.reinstall()
+    logger.info("Child")
+    deeper_subworker()
+
+
+def deeper_subworker():
+    logger.info("Grandchild")
+
+
+@pytest.mark.skipif(os.name == "nt", reason="Windows does not support forking")
+def test_process_fork(fork_context):
+    writer = Writer()
+
+    logger.add(writer, context=fork_context, format="{message}", enqueue=True, catch=False)
+
+    process = fork_context.Process(target=subworker, args=(logger,))
+    process.start()
+    process.join()
+
+    assert process.exitcode == 0
+
+    logger.info("Main")
+    logger.remove()
+
+    assert writer.read() == "Child\nGrandchild\nMain\n"
+
+
+def test_process_spawn(spawn_context):
+    writer = Writer()
+
+    logger.add(writer, context=spawn_context, format="{message}", enqueue=True, catch=False)
+
+    process = spawn_context.Process(target=subworker, args=(logger,))
+    process.start()
+    process.join()
+
+    assert process.exitcode == 0
+
+    logger.info("Main")
+    logger.remove()
+
+    assert writer.read() == "Child\nGrandchild\nMain\n"