[gevent] improving support for the new tracing API by palazzem · Pull Request #188 · DataDog/dd-trace-py

palazzem · 2017-02-17T18:23:36Z

What it does

Improves the gevent support for the new tracing API, through:

GeventContextProvider that provides the right Context to the tracer.trace() using the current Greenlet as a carrier
the gevent.Greenlet is overridden with the TracedGreenlet instance. It behaves the same way of the original Greenlet class, but it moves the Context among greenlets.

Flow

the main greenlet doesn't have a Context
when a greenlet is created, a new Context is attached only if the tracer is used
if a new greenlet is created from another greenlet, they share the same Context only if available in the invoker function

Usage

# even if not strictly required, it's better that the
# patch happens before importing gevent
from ddtrace import patch, tracer
patch(gevent=True)

import gevent
# do whatever you need and use tracer as usual

talwai · 2017-02-17T19:13:19Z

is there a reason why tracer.configure cannot happen by default in the ddtrace.contrib.gevent.patch? Is there an event where we would want to patch the Greenlet class but not the tracer's context provider

actually we don't have a way to patch things using the configure() method. I don't like having these two lines too because they're error prone (both are required). What I can do is:

having the class for this context provider that patches automatically the code like:

# even if not strictly required, it's better that the # patch happens before importing gevent from ddtrace import tracer from ddtrace.contrib.gevent import GeventContextProvider tracer.configure(context_provider=GeventContextProvider()) import gevent # do whatever you need

In that case, under the hood, the constructor will call the gevent patch()

i'm leaning towards:

from ddtrace import patch_all; patch_all(gevent=True)

calls tracer.configure() under the hood. Still I'm fine with either, i'll let you be the judge

oh gotcha.... yes that could be another option! I may check if it applies properly to other async modules, because I want to keep the API consistent among them.

talwai · 2017-02-17T19:19:20Z

reuse CONTEXT_ATTR ?

talwai · 2017-02-17T19:33:57Z

does testing suggest we need the latter two patches? i would think these shortcuts end up initializing a new gevent.Greenlet anyway which is aliased to a TracedGreenlet?

These shortcuts are replaced because gevent module keeps the original reference for the Greenlet class. Because both are class methods, it means that when they're used, the original class will be initialized.

(If I remove them, tests will fail)

LeoCavaille

Some minor docs nitpick, the code lgtm, it's really easy to read through with the context notion.

LeoCavaille · 2017-02-23T14:01:38Z

 """
-To trace a request in a gevent-ed environment, configure the tracer to use greenlet-local
-storage, rather than the default thread-local storage.
+To trace a request in a gevent-ed environment, configure the tracer to use the Greenlet


gevent-ed sounds weird? gevent?

LeoCavaille · 2017-02-23T14:02:05Z

-To trace a request in a gevent-ed environment, configure the tracer to use greenlet-local
-storage, rather than the default thread-local storage.
+To trace a request in a gevent-ed environment, configure the tracer to use the Greenlet
+context provider, rather than the default one that relies in thread-local storaging.


relies in -> relies on

LeoCavaille · 2017-02-23T14:03:20Z

+    ``Greenlet`` class that is used to replace the original ``gevent``
+    class. This class is supposed to do ``Context`` replacing operation, so
+    that any greenlet inherits the context from the parent Greenlet.
+    When a new greenlet is spawn from the main greenlet, a new instance


LotharSee

Very good work, looking great! It is all good to me.

…llocator (#17664) ## Description This PR fixes a segmentation fault in the memory allocation profiler that occurs when a hook call races with `memalloc` start/stop operations. The issue arises from concurrent access to the saved allocator struct, which could be partially written while being read, resulting in`NULL` function pointers being dereferenced. The key indicator in that case is that `#1 0x0000000000000000` frame -- we are trying to execute a null function pointer. ```` Error UnixSignal: Process terminated with SEGV_MAPERR (SIGSEGV) #0 0x00007ff3c303a8d4 #1 0x0000000000000000 memalloc_alloc (/go/src/github.com/DataDog/apm-reliability/dd-trace-py/ddtrace/profiling/collector/_memalloc.cpp:68) #2 0x00007ff39dcb3b20 memalloc_alloc (/go/src/github.com/DataDog/apm-reliability/dd-trace-py/ddtrace/profiling/collector/_memalloc.cpp:68) #3 0x00007ff39dcb3b20 memalloc_malloc(void*, unsigned long) (/go/src/github.com/DataDog/apm-reliability/dd-trace-py/ddtrace/profiling/collector/_memalloc.cpp:80) #4 0x00007ff3c3087e1b PyUnicode_New #5 0x00007ff3c30889f4 #6 0x00007ff3c3170c84 #7 0x00007ff3c316b931 #8 0x00007ff3c31aaac8 #9 0x00007ff3c31033ac #10 0x00007ff3c310e2a6 PyObject_CallMethodObjArgs #11 0x00007ff3c310e46d #12 0x00007ff3c31a96c2 #13 0x00007ff3c3102fd7 PyObject_Vectorcall #14 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #15 0x00007ff3c323c094 #16 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #17 0x00007ff3c323c094 #18 0x00007ff3c30e997d PyObject_CallOneArg #19 0x00007ff3c306a480 _PyObject_GenericGetAttrWithDict #20 0x00007ff3c30c620d PyObject_GetAttr #21 0x00007ff3c32309e7 _PyEval_EvalFrameDefault #22 0x00007ff3c323c094 #23 0x00007ff3c312880e #24 0x00007ff3c30e917c _PyObject_MakeTpCall #25 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #26 0x00007ff3c323c094 #27 0x00007ff3c312880e #28 0x00007ff3c30e917c _PyObject_MakeTpCall #29 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #30 0x00007ff3c323c094 #31 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #32 0x00007ff3c323c094 #33 0x00007ff3c317d0fd #34 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #35 0x00007ff3c323c094 #36 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #37 0x00007ff3c323c094 #38 0x00007ff3c317d1b5 #39 0x00007ff3c3102fd7 PyObject_Vectorcall #40 0x00007ff3c3232f4a _PyEval_EvalFrameDefault #41 0x00007ff3c3240da5 #42 0x00007ff3c324112d #43 0x00007ff3c3233be1 _PyEval_EvalFrameDefault #44 0x00007ff3c323c094 #45 0x00007ff3c317d1b5 #46 0x00007ff3c3102fd7 PyObject_Vectorcall #47 0x00007ff3c3232f4a _PyEval_EvalFrameDefault #48 0x00007ff3c323c094 #49 0x00007ff3c31033ac #50 0x00007ff3c310358d PyObject_CallFunctionObjArgs #51 0x00007ff3bf7eb91d WraptBoundFunctionWrapper_call (/project/src/wrapt/_wrappers.c:3750) #52 0x00007ff3c3104055 _PyObject_Call #53 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #54 0x00007ff3c323c094 #55 0x00007ff3c317d23c #56 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #57 0x00007ff3c323c094 #58 0x00007ff3c310416f _PyObject_Call #59 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #60 0x00007ff3c3240da5 #61 0x00007ff3c324112d #62 0x00007ff3c3233be1 _PyEval_EvalFrameDefault #63 0x00007ff3c323c094 #64 0x00007ff3c317d1b5 #65 0x00007ff3c3102fd7 PyObject_Vectorcall #66 0x00007ff3c3232f4a _PyEval_EvalFrameDefault #67 0x00007ff3c323c094 #68 0x00007ff3c317d1b5 #69 0x00007ff3c310416f _PyObject_Call #70 0x00007ff3c3233dd3 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_PyObject_FastCallDictTstate #173 0x00007ff3c30e958d _PyObject_Call_Prepend #174 0x00007ff3c3109150 #175 0x00007ff3c30e917c _PyObject_MakeTpCall #176 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #177 0x00007ff3c323c094 #178 0x00007ff3c30e92f1 _PyObject_FastCallDictTstate #179 0x00007ff3c30e958d _PyObject_Call_Prepend #180 0x00007ff3c3109150 #181 0x00007ff3c30e917c _PyObject_MakeTpCall #182 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #183 0x00007ff3c323c094 #184 0x00007ff3c30e92f1 _PyObject_FastCallDictTstate #185 0x00007ff3c30e958d _PyObject_Call_Prepend #186 0x00007ff3c3109150 #187 0x00007ff3c30e917c _PyObject_MakeTpCall #188 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #189 0x00007ff3c323c094 #190 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #191 0x00007ff3c323c094 #192 0x00007ff3c30e92f1 _PyObject_FastCallDictTstate #193 0x00007ff3c30e958d _PyObject_Call_Prepend #194 0x00007ff3c3109150 #195 0x00007ff3c30e917c _PyObject_MakeTpCall #196 0x00007ff3c32335a2 _PyEval_EvalFrameDefault #197 0x00007ff3c323c094 #198 0x00007ff3c317d0fd #199 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #200 0x00007ff3c323c094 #201 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #202 0x00007ff3c323c094 #203 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #204 0x00007ff3c323c094 #205 0x00007ff3c3233dd3 _PyEval_EvalFrameDefault #206 0x00007ff3c323c094 #207 0x00007ff3c317d23c #208 0x00007ff3c31a7ec5 #209 0x00007ff3c301ac77 #210 0x00007ff3c357c573 ```` The fix implements two key changes. 1. **Hook functions (`memalloc_alloc`, `memalloc_realloc`)**: Snapshot the allocator struct locally before use and guard indirect function calls with `NULL` checks. This prevents crashes if a partially-written struct is observed during a start/stop race. 2. **Start/stop operations (`memalloc_start`, `memalloc_stop`)**: Use local variables and single assignments when publishing the allocator struct to `global_memalloc_ctx.pymem_allocator_obj`. This ensures concurrent hook calls observe either the old or new struct, never a partially-written intermediate state. The real root cause is that `PyMem_GetAllocator` is not documented as atomic, and the struct could be read field-by-field while being written to concurrently. By using local copies and single assignments, we ensure atomicity at the C level and prevent observation of inconsistent state. Co-authored-by: thomas.kowalski <thomas.kowalski@datadoghq.com>

palazzem added the integrations label Feb 17, 2017

palazzem mentioned this pull request Feb 17, 2017

add asynchronous support for the current Tracer #161

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6 tasks

palazzem force-pushed the palazzem/gevent-support branch 2 times, most recently from 6d812a5 to 8dc1941 Compare February 17, 2017 18:40

talwai reviewed Feb 17, 2017

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palazzem force-pushed the palazzem/gevent-support branch from 6ff5410 to 12ddefa Compare February 17, 2017 19:53

palazzem requested a review from LotharSee February 17, 2017 19:54

palazzem force-pushed the palazzem/async-python branch from 0477cab to 18a90b3 Compare February 20, 2017 10:43

[gevent] removing gevent buffer implementation

5789690

palazzem force-pushed the palazzem/gevent-support branch from 6bbb11f to 76987da Compare February 20, 2017 10:44

Emanuele Palazzetti added 4 commits February 20, 2017 11:46

[gevent] using GeventContextProvider with a TracedGreenlet class

4ac1c02

[gevent] provide tests for 1.2; better tox matrix

c191de3

[gevent] using CONTEXT_ATTR in the greenlet class

61005fe

[gevent] add more testing for spawn_later classmethod

6192bb2

palazzem force-pushed the palazzem/gevent-support branch from 76987da to 6192bb2 Compare February 20, 2017 10:46

Emanuele Palazzetti added 2 commits February 20, 2017 11:49

[gevent] wrong renaming of asyncio provider comment

045a5c4

[gevent] patch automatically configures the Greenlet context provider

6f1d157

palazzem added this to the 0.6.0 milestone Feb 20, 2017

palazzem assigned LotharSee Feb 22, 2017

LeoCavaille approved these changes Feb 23, 2017

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[gevent] updating docs

4cd4faa

LotharSee approved these changes Feb 24, 2017

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Merge branch 'palazzem/async-python' into palazzem/gevent-support

fa2ad39

palazzem merged commit 52b9ba7 into palazzem/async-python Mar 1, 2017

palazzem deleted the palazzem/gevent-support branch March 1, 2017 12:25

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palazzem commented Feb 17, 2017 •

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