Limit stack traces in debug mode to make it faster.

Mirrors asyncio PR: python/cpython#4322

Author: 1st1

uvloop/cbhandles.pyx

@@ -12,7 +12,7 @@ cdef class Handle:
             loop._debug_cb_handles_total += 1
             loop._debug_cb_handles_count += 1
         if loop._debug:
-            self._source_traceback = tb_extract_stack(sys_getframe(0))
+            self._source_traceback = extract_stack()
 
     def __dealloc__(self):
         if UVLOOP_DEBUG and self.loop is not None:
@@ -133,7 +133,7 @@ cdef class TimerHandle:
         self.closed = 0
 
         if loop._debug:
-            self._source_traceback = tb_extract_stack(sys_getframe(0))
+            self._source_traceback = extract_stack()
 
         self.timer = UVTimer.new(
             loop, <method_t>self._run, self, delay)
@@ -310,3 +310,22 @@ cdef new_MethodHandle3(Loop loop, str name, method3_t callback, object ctx,
     handle.arg4 = arg3
 
     return handle
+
+
+cdef extract_stack():
+    """Replacement for traceback.extract_stack() that only does the
+    necessary work for asyncio debug mode.
+    """
+    f = sys_getframe()
+    if f is None:
+        return
+
+    try:
+        stack = tb_StackSummary.extract(tb_walk_stack(f),
+                                        limit=DEBUG_STACK_DEPTH,
+                                        lookup_lines=False)
+    finally:
+        f = None
+
+    stack.reverse()
+    return stack

uvloop/handles/handle.pyx

@@ -113,7 +113,7 @@ cdef class UVHandle:
         self._inited = 1
         self._handle.data = <void*>self
         if self._loop._debug:
-            self._source_traceback = tb_extract_stack(sys_getframe(0))
+            self._source_traceback = extract_stack()
         if UVLOOP_DEBUG:
             self._loop._debug_uv_handles_total += 1
 

uvloop/includes/consts.pxi

@@ -5,5 +5,7 @@ DEF FLOW_CONTROL_LOW_WATER = 16384
 
 DEF DEFAULT_FREELIST_SIZE = 250
 
+DEF DEBUG_STACK_DEPTH = 10
+
 
 DEF __PROCESS_DEBUG_SLEEP_AFTER_FORK = 1

uvloop/includes/stdlib.pxi

@@ -121,7 +121,8 @@ cdef signal_SIG_DFL = std_signal.SIG_DFL
 cdef time_sleep = time.sleep
 cdef time_monotonic = time.monotonic
 
-cdef tb_extract_stack = traceback.extract_stack
+cdef tb_StackSummary = traceback.StackSummary
+cdef tb_walk_stack = traceback.walk_stack
 cdef tb_format_list = traceback.format_list
 
 cdef warnings_warn = warnings.warn