Catch and display expceptions during multiprocessing bootstrap.

2 files changed, 30 insertions, 5 deletions

diff --git a/coverage/multiproc.py b/coverage/multiproc.py
index bab81475..c466301f 100644
--- a/coverage/multiproc.py
+++ b/coverage/multiproc.py
@@ -6,6 +6,8 @@
 import multiprocessing
 import multiprocessing.process
 import os
+import sys
+import traceback
 
 from coverage import env
 from coverage.misc import contract
@@ -27,14 +29,20 @@ class ProcessWithCoverage(OriginalProcess):         # pylint: disable=abstract-m
 
     def _bootstrap(self, *args, **kwargs):          # pylint: disable=arguments-differ
         """Wrapper around _bootstrap to start coverage."""
-        from coverage import Coverage       # avoid circular import
-        cov = Coverage(data_suffix=True)
-        cov._warn_preimported_source = False
-        cov.start()
-        debug = cov._debug
         try:
+            from coverage import Coverage       # avoid circular import
+            cov = Coverage(data_suffix=True)
+            cov._warn_preimported_source = False
+            cov.start()
+            debug = cov._debug
             if debug.should("multiproc"):
                 debug.write("Calling multiprocessing bootstrap")
+        except Exception:
+            print("Exception during multiprocessing bootstrap init:")
+            traceback.print_exc(file=sys.stdout)
+            sys.stdout.flush()
+            raise
+        try:
             return original_bootstrap(self, *args, **kwargs)
         finally:
             if debug.should("multiproc"):
diff --git a/tests/test_concurrency.py b/tests/test_concurrency.py
index 436df803..3a127499 100644
--- a/tests/test_concurrency.py
+++ b/tests/test_concurrency.py
@@ -476,6 +476,23 @@ class MultiprocessingTest(CoverageTest):
         expected_out = "{nprocs} pids, total = {total}".format(nprocs=nprocs, total=total)
         self.try_multiprocessing_code_with_branching(code, expected_out)
 
+    def test_multiprocessing_bootstrap_error_handling(self):
+        # An exception during bootstrapping will be reported.
+        self.make_file("multi.py", """\
+            import multiprocessing
+            if __name__ == "__main__":
+                with multiprocessing.Manager():
+                    pass
+            """)
+        self.make_file(".coveragerc", """\
+            [run]
+            concurrency = multiprocessing
+            _crash = _bootstrap
+            """)
+        out = self.run_command("coverage run multi.py")
+        self.assertIn("Exception during multiprocessing bootstrap init", out)
+        self.assertIn("Exception: Crashing because called by _bootstrap", out)
+
 
 def test_coverage_stop_in_threads():
     has_started_coverage = []