add stacktracer.py: helper util to debug threading issues

taken from https://code.activestate.com/recipes/577334-how-to-debug-deadlocked-multi-threaded-programs/

electrum/utils/stacktracer.py

@@ -0,0 +1,132 @@
+#!/usr/bin/env python
+#
+# Copyright (C) 2010 Laszlo Nagy (nagylzs)
+#
+# Permission is hereby granted, free of charge, to any person
+# obtaining a copy of this software and associated documentation files
+# (the "Software"), to deal in the Software without restriction,
+# including without limitation the rights to use, copy, modify, merge,
+# publish, distribute, sublicense, and/or sell copies of the Software,
+# and to permit persons to whom the Software is furnished to do so,
+# subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be
+# included in all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+#
+# Taken from: https://code.activestate.com/recipes/577334-how-to-debug-deadlocked-multi-threaded-programs/
+
+
+"""Stack tracer for multi-threaded applications.
+
+
+Usage:
+
+import stacktracer
+stacktracer.start_trace("trace.html",interval=5,auto=True) # Set auto flag to always update file!
+....
+stacktracer.stop_trace()
+"""
+
+import sys
+import traceback
+from pygments import highlight
+from pygments.lexers import PythonLexer
+from pygments.formatters import HtmlFormatter
+
+
+# Taken from http://bzimmer.ziclix.com/2008/12/17/python-thread-dumps/
+
+def stacktraces():
+    code = []
+    for threadId, stack in sys._current_frames().items():
+        code.append("\n# ThreadID: %s" % threadId)
+        for filename, lineno, name, line in traceback.extract_stack(stack):
+            code.append('File: "%s", line %d, in %s' % (filename, lineno, name))
+            if line:
+                code.append("  %s" % (line.strip()))
+
+    return highlight("\n".join(code), PythonLexer(), HtmlFormatter(
+        full=False,
+        # style="native",
+        noclasses=True,
+    ))
+
+
+# This part was made by nagylzs
+import os
+import time
+import threading
+
+
+class TraceDumper(threading.Thread):
+    """Dump stack traces into a given file periodically."""
+
+    def __init__(self, fpath, interval, auto):
+        """
+        @param fpath: File path to output HTML (stack trace file)
+        @param auto: Set flag (True) to update trace continuously.
+            Clear flag (False) to update only if file not exists.
+            (Then delete the file to force update.)
+        @param interval: In seconds: how often to update the trace file.
+        """
+        assert (interval > 0.1)
+        self.auto = auto
+        self.interval = interval
+        self.fpath = os.path.abspath(fpath)
+        self.stop_requested = threading.Event()
+        threading.Thread.__init__(self)
+
+    def run(self):
+        while not self.stop_requested.isSet():
+            time.sleep(self.interval)
+            if self.auto or not os.path.isfile(self.fpath):
+                self.stacktraces()
+
+    def stop(self):
+        self.stop_requested.set()
+        self.join()
+        try:
+            if os.path.isfile(self.fpath):
+                os.unlink(self.fpath)
+        except:
+            pass
+
+    def stacktraces(self):
+        fout = file(self.fpath, "wb+")
+        try:
+            fout.write(stacktraces())
+        finally:
+            fout.close()
+
+
+_tracer = None
+
+
+def trace_start(fpath, interval=5, auto=True):
+    """Start tracing into the given file."""
+    global _tracer
+    if _tracer is None:
+        _tracer = TraceDumper(fpath, interval, auto)
+        _tracer.setDaemon(True)
+        _tracer.start()
+    else:
+        raise Exception("Already tracing to %s" % _tracer.fpath)
+
+
+def trace_stop():
+    """Stop tracing."""
+    global _tracer
+    if _tracer is None:
+        raise Exception("Not tracing, cannot stop.")
+    else:
+        _trace.stop()
+        _trace = None