From 7134c0bb05b29a16127b634d9ac253b457f137cb Mon Sep 17 00:00:00 2001
From: Bastian Kleineidam <bastian.kleineidam@web.de>
Date: Tue, 22 Jan 2013 18:16:53 +0100
Subject: [PATCH] Print thread stack traces on SIGUSR1

---
 doc/changelog.txt     |  2 ++
 linkcheck/__init__.py | 18 ++++++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/doc/changelog.txt b/doc/changelog.txt
index 4581e9df..fefa3ea3 100644
--- a/doc/changelog.txt
+++ b/doc/changelog.txt
@@ -2,6 +2,8 @@
 
 Features:
 - checking: Support <link rel="dns-prefetch"> URLs.
+- logging: Sending SIGUSR1 signal prints the stack trace of all current
+  running threads. This makes it easier to debug deadlocks.
 
 Fixes:
 - checking: Fix a crash when closing a Word document after scanning failed.
diff --git a/linkcheck/__init__.py b/linkcheck/__init__.py
index 1364b41f..3c704886 100644
--- a/linkcheck/__init__.py
+++ b/linkcheck/__init__.py
@@ -32,6 +32,8 @@ if _dnspath not in sys.path:
     sys.path.insert(0, _dnspath)
 del _dnspath
 import re
+import signal
+import traceback
 
 from . import i18n
 import _LinkChecker_configdata as configdata
@@ -176,3 +178,19 @@ def find_third_party_modules ():
         sys.path.append(os.path.join(third_party, "dnspython"))
 
 find_third_party_modules()
+
+# install SIGUSR1 handler
+from .decorators import signal_handler
+@signal_handler(signal.SIGUSR1)
+def print_threadstacks(sig, frame):
+    """Print stack traces of all running threads."""
+    log.warn(LOG_THREAD, "*** STACKTRACE START ***")
+    for threadId, stack in sys._current_frames().items():
+        log.warn(LOG_THREAD, "# ThreadID: %s" % threadId)
+        for filename, lineno, name, line in traceback.extract_stack(stack):
+            log.warn(LOG_THREAD, 'File: "%s", line %d, in %s' % (filename, lineno, name))
+            line = line.strip()
+            if line:
+                log.warn(LOG_THREAD, "  %s" % line)
+    log.warn(LOG_THREAD, "*** STACKTRACE END ***")
+