Switch test_stress_delivery_simultaneous from SIGUSR1 to SIGUSR2

Author: mhsmith

Android/testbed/app/src/main/python/main.py

@@ -5,9 +5,22 @@
 import sys
 
 # Some tests use SIGUSR1, but that's blocked by default in an Android app in
-# order to make it available to `sigwait` in the "Signal Catcher" thread. That
-# thread's functionality is only relevant to the JVM ("forcing GC (no HPROF) and
-# profile save"), so disabling it should not weaken the tests.
+# order to make it available to `sigwait` in the Signal Catcher thread. That
+# thread's functionality is only useful for debugging the JVM, so disabling it
+# should not weaken the tests.
+#
+# Simply unblocking SIGUSR1 is enough to fix most tests that use it. But in
+# tests that generate multiple different signals in quick succession, it's
+# possible for SIGUSR1 to arrive while the main thread is busy running the
+# C-level handler for a different signal, in which case the SIGUSR1 may be sent
+# to the Signal Catcher thread instead. When this happens, there will be a log
+# message containing the text "reacting to signal".
+#
+# In such cases, the tests may need to be changed. Possible workarounds include:
+#   * Use a signal other than SIGUSR1 (e.g. test_stress_delivery_simultaneous in
+#     test_signal.py).
+#   * Send the signal to a specific thread rather than the whole process (e.g.
+#     test_signals in test_threadsignals.py.
 signal.pthread_sigmask(signal.SIG_UNBLOCK, [signal.SIGUSR1])
 
 sys.argv[1:] = shlex.split(os.environ["PYTHON_ARGS"])

Lib/test/test_signal.py

@@ -1325,15 +1325,18 @@ def test_stress_delivery_simultaneous(self):
         def handler(signum, frame):
             sigs.append(signum)
 
-        self.setsig(signal.SIGUSR1, handler)
+        # On Android, SIGUSR1 is unreliable when used in close proximity to
+        # another signal – see Android/testbed/app/src/main/python/main.py.
+        # So we use a different signal.
+        self.setsig(signal.SIGUSR2, handler)
         self.setsig(signal.SIGALRM, handler)  # for ITIMER_REAL
 
         expected_sigs = 0
         while expected_sigs < N:
             # Hopefully the SIGALRM will be received somewhere during
-            # initial processing of SIGUSR1.
+            # initial processing of SIGUSR2.
             signal.setitimer(signal.ITIMER_REAL, 1e-6 + random.random() * 1e-5)
-            os.kill(os.getpid(), signal.SIGUSR1)
+            os.kill(os.getpid(), signal.SIGUSR2)
 
             expected_sigs += 2
             # Wait for handlers to run to avoid signal coalescing