issue #150: import stack.py hack as mitogen.debug

Usage:
  - insert a call to mitogen.debug() in the desired process
  - kill -USR2 that process
  - observe its controlling TTY produces thread stack dumps

mitogen/debug.py

+# Copyright 2017, David Wilson
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# 1. Redistributions of source code must retain the above copyright notice,
+# this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright notice,
+# this list of conditions and the following disclaimer in the documentation
+# and/or other materials provided with the distribution.
+#
+# 3. Neither the name of the copyright holder nor the names of its contributors
+# may be used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+
+"""
+Basic signal handler for dumping thread stacks.
+"""
+
+import difflib
+import os
+import signal
+import sys
+import threading
+import time
+import traceback
+
+
+_last = None
+
+
+def format_stacks():
+    name_by_id = {
+        t.ident: t.name
+        for t in threading.enumerate()
+    }
+
+    l = ['', '']
+    for threadId, stack in sys._current_frames().items():
+        l += ["# PID %d ThreadID: (%s) %s; %r" % (
+            os.getpid(),
+            name_by_id.get(threadId, '<no name>'),
+            threadId,
+            stack,
+        )]
+
+        for filename, lineno, name, line in traceback.extract_stack(stack):
+            l += [
+                'File: "%s", line %d, in %s' % (
+                    filename,
+                    lineno,
+                    name
+                )
+            ]
+            if line:
+                l += ['    ' + line.strip()]
+        l += ['']
+
+    l += ['', '']
+    return '\n'.join(l)
+
+
+def _handler(*_):
+    global _last
+
+    s = format_stacks()
+    fp = open('/dev/tty', 'w', 1)
+    fp.write(s)
+
+    if _last:
+        fp.write('\n')
+        diff = list(difflib.unified_diff(
+            a=_last.splitlines(),
+            b=s.splitlines(),
+            fromfile='then',
+            tofile='now'
+        ))
+
+        if diff:
+            fp.write('\n'.join(diff))
+        else:
+            fp.write('(no change since last time)\n')
+    _last = s
+
+
+def install_handler():
+    signal.signal(signal.SIGUSR2, _handler)
+
+
+def _thread_main():
+    while True:
+        time.sleep(7)
+        l = format_stacks()
+        open('/tmp/stack.%s.log' % (os.getpid(),), 'wb', 65535).write(l)
+        break
+
+
+def dump_periodically():
+    th = threading.Thread(target=main)
+    th.setDaemon(True)
+    th.start()