bpo-37961, tracemalloc: add Traceback.total_nframe (GH-15545)

Add a total_nframe field to the traces collected by the tracemalloc module.
This field indicates the original number of frames before it was truncated.

Doc/library/tracemalloc.rst

@@ -313,6 +313,9 @@ Functions
    frames. By default, a trace of a memory block only stores the most recent
    frame: the limit is ``1``. *nframe* must be greater or equal to ``1``.
 
+   You can still read the original number of total frames that composed the
+   traceback by looking at the :attr:`Traceback.total_nframe` attribute.
+
    Storing more than ``1`` frame is only useful to compute statistics grouped
    by ``'traceback'`` or to compute cumulative statistics: see the
    :meth:`Snapshot.compare_to` and :meth:`Snapshot.statistics` methods.
@@ -659,6 +662,9 @@ Traceback
 
    When a snapshot is taken, tracebacks of traces are limited to
    :func:`get_traceback_limit` frames. See the :func:`take_snapshot` function.
+   The original number of frames of the traceback is stored in the
+   :attr:`Traceback.total_nframe` attribute. That allows to know if a traceback
+   has been truncated by the traceback limit.
 
    The :attr:`Trace.traceback` attribute is an instance of :class:`Traceback`
    instance.
@@ -666,6 +672,15 @@ Traceback
    .. versionchanged:: 3.7
       Frames are now sorted from the oldest to the most recent, instead of most recent to oldest.
 
+   .. attribute:: total_nframe
+
+      Total number of frames that composed the traceback before truncation.
+      This attribute can be set to ``None`` if the information is not
+      available.
+
+   .. versionchanged:: 3.9
+      The :attr:`Traceback.total_nframe` attribute was added.
+
    .. method:: format(limit=None, most_recent_first=False)
 
       Format the traceback as a list of lines with newlines. Use the

Lib/test/test_tracemalloc.py

@@ -36,7 +36,7 @@ def allocate_bytes(size):
     bytes_len = (size - EMPTY_STRING_SIZE)
     frames = get_frames(nframe, 1)
     data = b'x' * bytes_len
-    return data, tracemalloc.Traceback(frames)
+    return data, tracemalloc.Traceback(frames, min(len(frames), nframe))
 
 def create_snapshots():
     traceback_limit = 2
@@ -45,27 +45,27 @@ def create_snapshots():
     # traceback_frames) tuples. traceback_frames is a tuple of (filename,
     # line_number) tuples.
     raw_traces = [
-        (0, 10, (('a.py', 2), ('b.py', 4))),
-        (0, 10, (('a.py', 2), ('b.py', 4))),
-        (0, 10, (('a.py', 2), ('b.py', 4))),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
 
-        (1, 2, (('a.py', 5), ('b.py', 4))),
+        (1, 2, (('a.py', 5), ('b.py', 4)), 3),
 
-        (2, 66, (('b.py', 1),)),
+        (2, 66, (('b.py', 1),), 1),
 
-        (3, 7, (('<unknown>', 0),)),
+        (3, 7, (('<unknown>', 0),), 1),
     ]
     snapshot = tracemalloc.Snapshot(raw_traces, traceback_limit)
 
     raw_traces2 = [
-        (0, 10, (('a.py', 2), ('b.py', 4))),
-        (0, 10, (('a.py', 2), ('b.py', 4))),
-        (0, 10, (('a.py', 2), ('b.py', 4))),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+        (0, 10, (('a.py', 2), ('b.py', 4)), 3),
 
-        (2, 2, (('a.py', 5), ('b.py', 4))),
-        (2, 5000, (('a.py', 5), ('b.py', 4))),
+        (2, 2, (('a.py', 5), ('b.py', 4)), 3),
+        (2, 5000, (('a.py', 5), ('b.py', 4)), 3),
 
-        (4, 400, (('c.py', 578),)),
+        (4, 400, (('c.py', 578),), 1),
     ]
     snapshot2 = tracemalloc.Snapshot(raw_traces2, traceback_limit)
 
@@ -125,7 +125,7 @@ class TestTracemallocEnabled(unittest.TestCase):
 
         nframe = tracemalloc.get_traceback_limit()
         frames = get_frames(nframe, -3)
-        obj_traceback = tracemalloc.Traceback(frames)
+        obj_traceback = tracemalloc.Traceback(frames, min(len(frames), nframe))
 
         traceback = tracemalloc.get_object_traceback(obj)
         self.assertIsNotNone(traceback)
@@ -167,7 +167,7 @@ class TestTracemallocEnabled(unittest.TestCase):
         trace = self.find_trace(traces, obj_traceback)
 
         self.assertIsInstance(trace, tuple)
-        domain, size, traceback = trace
+        domain, size, traceback, length = trace
         self.assertEqual(size, obj_size)
         self.assertEqual(traceback, obj_traceback._frames)
 
@@ -197,8 +197,8 @@ class TestTracemallocEnabled(unittest.TestCase):
 
         trace1 = self.find_trace(traces, obj1_traceback)
         trace2 = self.find_trace(traces, obj2_traceback)
-        domain1, size1, traceback1 = trace1
-        domain2, size2, traceback2 = trace2
+        domain1, size1, traceback1, length1 = trace1
+        domain2, size2, traceback2, length2 = trace2
         self.assertIs(traceback2, traceback1)
 
     def test_get_traced_memory(self):
@@ -259,6 +259,9 @@ class TestTracemallocEnabled(unittest.TestCase):
         # take a snapshot
         snapshot = tracemalloc.take_snapshot()
 
+        # This can vary
+        self.assertGreater(snapshot.traces[1].traceback.total_nframe, 10)
+
         # write on disk
         snapshot.dump(support.TESTFN)
         self.addCleanup(support.unlink, support.TESTFN)
@@ -321,7 +324,7 @@ class TestSnapshot(unittest.TestCase):
     maxDiff = 4000
 
     def test_create_snapshot(self):
-        raw_traces = [(0, 5, (('a.py', 2),))]
+        raw_traces = [(0, 5, (('a.py', 2),), 10)]
 
         with contextlib.ExitStack() as stack:
             stack.enter_context(patch.object(tracemalloc, 'is_tracing',
@@ -336,6 +339,7 @@ class TestSnapshot(unittest.TestCase):
             self.assertEqual(len(snapshot.traces), 1)
             trace = snapshot.traces[0]
             self.assertEqual(trace.size, 5)
+            self.assertEqual(trace.traceback.total_nframe, 10)
             self.assertEqual(len(trace.traceback), 1)
             self.assertEqual(trace.traceback[0].filename, 'a.py')
             self.assertEqual(trace.traceback[0].lineno, 2)
@@ -351,11 +355,11 @@ class TestSnapshot(unittest.TestCase):
         # exclude b.py
         snapshot3 = snapshot.filter_traces((filter1,))
         self.assertEqual(snapshot3.traces._traces, [
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (1, 2, (('a.py', 5), ('b.py', 4))),
-            (3, 7, (('<unknown>', 0),)),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (1, 2, (('a.py', 5), ('b.py', 4)), 3),
+            (3, 7, (('<unknown>', 0),), 1),
         ])
 
         # filter_traces() must not touch the original snapshot
@@ -364,10 +368,10 @@ class TestSnapshot(unittest.TestCase):
         # only include two lines of a.py
         snapshot4 = snapshot3.filter_traces((filter2, filter3))
         self.assertEqual(snapshot4.traces._traces, [
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (1, 2, (('a.py', 5), ('b.py', 4))),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (1, 2, (('a.py', 5), ('b.py', 4)), 3),
         ])
 
         # No filter: just duplicate the snapshot
@@ -388,21 +392,21 @@ class TestSnapshot(unittest.TestCase):
         # exclude a.py of domain 1
         snapshot3 = snapshot.filter_traces((filter1,))
         self.assertEqual(snapshot3.traces._traces, [
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (2, 66, (('b.py', 1),)),
-            (3, 7, (('<unknown>', 0),)),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (2, 66, (('b.py', 1),), 1),
+            (3, 7, (('<unknown>', 0),), 1),
         ])
 
         # include domain 1
         snapshot3 = snapshot.filter_traces((filter1,))
         self.assertEqual(snapshot3.traces._traces, [
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (2, 66, (('b.py', 1),)),
-            (3, 7, (('<unknown>', 0),)),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (2, 66, (('b.py', 1),), 1),
+            (3, 7, (('<unknown>', 0),), 1),
         ])
 
     def test_filter_traces_domain_filter(self):
@@ -413,17 +417,17 @@ class TestSnapshot(unittest.TestCase):
         # exclude domain 2
         snapshot3 = snapshot.filter_traces((filter1,))
         self.assertEqual(snapshot3.traces._traces, [
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (0, 10, (('a.py', 2), ('b.py', 4))),
-            (1, 2, (('a.py', 5), ('b.py', 4))),
-            (2, 66, (('b.py', 1),)),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (0, 10, (('a.py', 2), ('b.py', 4)), 3),
+            (1, 2, (('a.py', 5), ('b.py', 4)), 3),
+            (2, 66, (('b.py', 1),), 1),
         ])
 
         # include domain 2
         snapshot3 = snapshot.filter_traces((filter2,))
         self.assertEqual(snapshot3.traces._traces, [
-            (3, 7, (('<unknown>', 0),)),
+            (3, 7, (('<unknown>', 0),), 1),
         ])
 
     def test_snapshot_group_by_line(self):

Lib/tracemalloc.py

@@ -182,15 +182,20 @@ class Traceback(Sequence):
     Sequence of Frame instances sorted from the oldest frame
     to the most recent frame.
     """
-    __slots__ = ("_frames",)
+    __slots__ = ("_frames", '_total_nframe')
 
-    def __init__(self, frames):
+    def __init__(self, frames, total_nframe=None):
         Sequence.__init__(self)
         # frames is a tuple of frame tuples: see Frame constructor for the
         # format of a frame tuple; it is reversed, because _tracemalloc
         # returns frames sorted from most recent to oldest, but the
         # Python API expects oldest to most recent
         self._frames = tuple(reversed(frames))
+        self._total_nframe = total_nframe
+
+    @property
+    def total_nframe(self):
+        return self._total_nframe
 
     def __len__(self):
         return len(self._frames)
@@ -221,7 +226,12 @@ class Traceback(Sequence):
         return str(self[0])
 
     def __repr__(self):
-        return "<Traceback %r>" % (tuple(self),)
+        s = "<Traceback %r" % tuple(self)
+        if self._total_nframe is None:
+            s += ">"
+        else:
+            s += f" total_nframe={self.total_nframe}>"
+        return s
 
     def format(self, limit=None, most_recent_first=False):
         lines = []
@@ -280,7 +290,7 @@ class Trace:
 
     @property
     def traceback(self):
-        return Traceback(self._trace[2])
+        return Traceback(*self._trace[2:])
 
     def __eq__(self, other):
         if not isinstance(other, Trace):
@@ -378,7 +388,7 @@ class Filter(BaseFilter):
             return self._match_frame(filename, lineno)
 
     def _match(self, trace):
-        domain, size, traceback = trace
+        domain, size, traceback, total_nframe = trace
         res = self._match_traceback(traceback)
         if self.domain is not None:
             if self.inclusive:
@@ -398,7 +408,7 @@ class DomainFilter(BaseFilter):
         return self._domain
 
     def _match(self, trace):
-        domain, size, traceback = trace
+        domain, size, traceback, total_nframe = trace
         return (domain == self.domain) ^ (not self.inclusive)
 
 
@@ -475,7 +485,7 @@ class Snapshot:
         tracebacks = {}
         if not cumulative:
             for trace in self.traces._traces:
-                domain, size, trace_traceback = trace
+                domain, size, trace_traceback, total_nframe = trace
                 try:
                     traceback = tracebacks[trace_traceback]
                 except KeyError:
@@ -496,7 +506,7 @@ class Snapshot:
         else:
             # cumulative statistics
             for trace in self.traces._traces:
-                domain, size, trace_traceback = trace
+                domain, size, trace_traceback, total_nframe = trace
                 for frame in trace_traceback:
                     try:
                         traceback = tracebacks[frame]

Misc/NEWS.d/next/Library/2019-08-27-10-30-44.bpo-37961.4nm0zZ.rst

+Add a ``total_nframe`` field to the traces collected by the tracemalloc module.
+This field indicates the original number of frames before it was truncated.

Modules/_tracemalloc.c

@@ -78,15 +78,20 @@ __attribute__((packed))
 
 typedef struct {
     Py_uhash_t hash;
-    int nframe;
+    /* Number of frames stored */
+    uint16_t nframe;
+    /* Total number of frames the traceback had */
+    uint16_t total_nframe;
     frame_t frames[1];
 } traceback_t;
 
 #define TRACEBACK_SIZE(NFRAME) \
         (sizeof(traceback_t) + sizeof(frame_t) * (NFRAME - 1))
 
-#define MAX_NFRAME \
-        ((INT_MAX - (int)sizeof(traceback_t)) / (int)sizeof(frame_t) + 1)
+/* The maximum number of frames is either:
+ - The maximum number of frames we can store in `traceback_t.nframe`
+ - The maximum memory size_t we can allocate */
+static const unsigned long MAX_NFRAME = Py_MIN(UINT16_MAX, ((SIZE_MAX - sizeof(traceback_t)) / sizeof(frame_t) + 1));
 
 
 static PyObject *unknown_filename = NULL;
@@ -308,6 +313,9 @@ hashtable_compare_traceback(_Py_hashtable_t *ht, const void *pkey,
     if (traceback1->nframe != traceback2->nframe)
         return 0;
 
+    if (traceback1->total_nframe != traceback2->total_nframe)
+        return 0;
+
     for (i=0; i < traceback1->nframe; i++) {
         frame1 = &traceback1->frames[i];
         frame2 = &traceback2->frames[i];
@@ -416,6 +424,7 @@ traceback_hash(traceback_t *traceback)
         /* the cast might truncate len; that doesn't change hash stability */
         mult += (Py_uhash_t)(82520UL + len + len);
     }
+    x ^= traceback->total_nframe;
     x += 97531UL;
     return x;
 }
@@ -436,11 +445,13 @@ traceback_get_frames(traceback_t *traceback)
     }
 
     for (pyframe = tstate->frame; pyframe != NULL; pyframe = pyframe->f_back) {
+        if (traceback->nframe < _Py_tracemalloc_config.max_nframe) {
             tracemalloc_get_frame(pyframe, &traceback->frames[traceback->nframe]);
             assert(traceback->frames[traceback->nframe].filename != NULL);
             traceback->nframe++;
-        if (traceback->nframe == _Py_tracemalloc_config.max_nframe)
-            break;
+        }
+        if (traceback->total_nframe < UINT16_MAX)
+            traceback->total_nframe++;
     }
 }
 
@@ -456,6 +467,7 @@ traceback_new(void)
     /* get frames */
     traceback = tracemalloc_traceback;
     traceback->nframe = 0;
+    traceback->total_nframe = 0;
     traceback_get_frames(traceback);
     if (traceback->nframe == 0)
         return &tracemalloc_empty_traceback;
@@ -1001,6 +1013,7 @@ tracemalloc_init(void)
     PyUnicode_InternInPlace(&unknown_filename);
 
     tracemalloc_empty_traceback.nframe = 1;
+    tracemalloc_empty_traceback.total_nframe = 1;
     /* borrowed reference */
     tracemalloc_empty_traceback.frames[0].filename = unknown_filename;
     tracemalloc_empty_traceback.frames[0].lineno = 0;
@@ -1046,10 +1059,10 @@ tracemalloc_start(int max_nframe)
     PyMemAllocatorEx alloc;
     size_t size;
 
-    if (max_nframe < 1 || max_nframe > MAX_NFRAME) {
+    if (max_nframe < 1 || (unsigned long) max_nframe > MAX_NFRAME) {
         PyErr_Format(PyExc_ValueError,
-                     "the number of frames must be in range [1; %i]",
-                     (int)MAX_NFRAME);
+                     "the number of frames must be in range [1; %lu]",
+                     MAX_NFRAME);
         return -1;
     }
 
@@ -1062,7 +1075,6 @@ tracemalloc_start(int max_nframe)
         return 0;
     }
 
-    assert(1 <= max_nframe && max_nframe <= MAX_NFRAME);
     _Py_tracemalloc_config.max_nframe = max_nframe;
 
     /* allocate a buffer to store a new traceback */
@@ -1234,7 +1246,7 @@ trace_to_pyobject(unsigned int domain, trace_t *trace,
     PyObject *trace_obj = NULL;
     PyObject *obj;
 
-    trace_obj = PyTuple_New(3);
+    trace_obj = PyTuple_New(4);
     if (trace_obj == NULL)
         return NULL;
 
@@ -1259,6 +1271,13 @@ trace_to_pyobject(unsigned int domain, trace_t *trace,
     }
     PyTuple_SET_ITEM(trace_obj, 2, obj);
 
+    obj = PyLong_FromUnsignedLong(trace->traceback->total_nframe);
+    if (obj == NULL) {
+        Py_DECREF(trace_obj);
+        return NULL;
+    }
+    PyTuple_SET_ITEM(trace_obj, 3, obj);
+
     return trace_obj;
 }