fix(profiling): Do not keep reference to frame to prevent memory leak (getsentry#2049)

The profiler can capture frames from it's own thread. When it does so, it holds
on to a reference to the frame in the previous sample. One of the frames it
holds on it is a frame from the profiler itself, which prevents the references
to other frames to other frames from being freed. A consequence of this is that
the local variables of those frames are not able to be freed either. This change
ensures we do not keep a reference to the profiler around in order to prevent
this issue.

Author: Zylphrex

mypy.ini

@@ -59,6 +59,8 @@ ignore_missing_imports = True
 [mypy-sentry_sdk._queue]
 ignore_missing_imports = True
 disallow_untyped_defs = False
+[mypy-sentry_sdk._lru_cache]
+disallow_untyped_defs = False
 [mypy-celery.app.trace]
 ignore_missing_imports = True
 [mypy-flask.signals]

sentry_sdk/_lru_cache.py

@@ -0,0 +1,156 @@
+"""
+A fork of Python 3.6's stdlib lru_cache (found in Python's 'cpython/Lib/functools.py')
+adapted into a data structure for single threaded uses.
+
+https://github.com/python/cpython/blob/v3.6.12/Lib/functools.py
+
+
+Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
+2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Python Software Foundation;
+
+All Rights Reserved
+
+
+PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+--------------------------------------------
+
+1. This LICENSE AGREEMENT is between the Python Software Foundation
+("PSF"), and the Individual or Organization ("Licensee") accessing and
+otherwise using this software ("Python") in source or binary form and
+its associated documentation.
+
+2. Subject to the terms and conditions of this License Agreement, PSF hereby
+grants Licensee a nonexclusive, royalty-free, world-wide license to reproduce,
+analyze, test, perform and/or display publicly, prepare derivative works,
+distribute, and otherwise use Python alone or in any derivative version,
+provided, however, that PSF's License Agreement and PSF's notice of copyright,
+i.e., "Copyright (c) 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
+2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020 Python Software Foundation;
+All Rights Reserved" are retained in Python alone or in any derivative version
+prepared by Licensee.
+
+3. In the event Licensee prepares a derivative work that is based on
+or incorporates Python or any part thereof, and wants to make
+the derivative work available to others as provided herein, then
+Licensee hereby agrees to include in any such work a brief summary of
+the changes made to Python.
+
+4. PSF is making Python available to Licensee on an "AS IS"
+basis.  PSF MAKES NO REPRESENTATIONS OR WARRANTIES, EXPRESS OR
+IMPLIED.  BY WAY OF EXAMPLE, BUT NOT LIMITATION, PSF MAKES NO AND
+DISCLAIMS ANY REPRESENTATION OR WARRANTY OF MERCHANTABILITY OR FITNESS
+FOR ANY PARTICULAR PURPOSE OR THAT THE USE OF PYTHON WILL NOT
+INFRINGE ANY THIRD PARTY RIGHTS.
+
+5. PSF SHALL NOT BE LIABLE TO LICENSEE OR ANY OTHER USERS OF PYTHON
+FOR ANY INCIDENTAL, SPECIAL, OR CONSEQUENTIAL DAMAGES OR LOSS AS
+A RESULT OF MODIFYING, DISTRIBUTING, OR OTHERWISE USING PYTHON,
+OR ANY DERIVATIVE THEREOF, EVEN IF ADVISED OF THE POSSIBILITY THEREOF.
+
+6. This License Agreement will automatically terminate upon a material
+breach of its terms and conditions.
+
+7. Nothing in this License Agreement shall be deemed to create any
+relationship of agency, partnership, or joint venture between PSF and
+Licensee.  This License Agreement does not grant permission to use PSF
+trademarks or trade name in a trademark sense to endorse or promote
+products or services of Licensee, or any third party.
+
+8. By copying, installing or otherwise using Python, Licensee
+agrees to be bound by the terms and conditions of this License
+Agreement.
+
+"""
+
+SENTINEL = object()
+
+
+# aliases to the entries in a node
+PREV = 0
+NEXT = 1
+KEY = 2
+VALUE = 3
+
+
+class LRUCache(object):
+    def __init__(self, max_size):
+        assert max_size > 0
+
+        self.max_size = max_size
+        self.full = False
+
+        self.cache = {}
+
+        # root of the circularly linked list to keep track of
+        # the least recently used key
+        self.root = []  # type: ignore
+        # the node looks like [PREV, NEXT, KEY, VALUE]
+        self.root[:] = [self.root, self.root, None, None]
+
+        self.hits = self.misses = 0
+
+    def set(self, key, value):
+        link = self.cache.get(key, SENTINEL)
+
+        if link is not SENTINEL:
+            # have to move the node to the front of the linked list
+            link_prev, link_next, _key, _value = link
+
+            # first remove the node from the lsnked list
+            link_prev[NEXT] = link_next
+            link_next[PREV] = link_prev
+
+            # insert the node between the root and the last
+            last = self.root[PREV]
+            last[NEXT] = self.root[PREV] = link
+            link[PREV] = last
+            link[NEXT] = self.root
+
+            # update the value
+            link[VALUE] = value
+
+        elif self.full:
+            # reuse the root node, so update its key/value
+            old_root = self.root
+            old_root[KEY] = key
+            old_root[VALUE] = value
+
+            self.root = old_root[NEXT]
+            old_key = self.root[KEY]
+
+            self.root[KEY] = self.root[VALUE] = None
+
+            del self.cache[old_key]
+
+            self.cache[key] = old_root
+
+        else:
+            # insert new node after last
+            last = self.root[PREV]
+            link = [last, self.root, key, value]
+            last[NEXT] = self.root[PREV] = self.cache[key] = link
+            self.full = len(self.cache) >= self.max_size
+
+    def get(self, key, default=None):
+        link = self.cache.get(key, SENTINEL)
+
+        if link is SENTINEL:
+            self.misses += 1
+            return default
+
+        # have to move the node to the front of the linked list
+        link_prev, link_next, _key, _value = link
+
+        # first remove the node from the lsnked list
+        link_prev[NEXT] = link_next
+        link_next[PREV] = link_prev
+
+        # insert the node between the root and the last
+        last = self.root[PREV]
+        last[NEXT] = self.root[PREV] = link
+        link[PREV] = last
+        link[NEXT] = self.root
+
+        self.hits += 1
+
+        return link[VALUE]