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Fix a class of logcontext leaks #3170
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So, it turns out that if you have a first `Deferred` `D1`, you can add a callback which returns another `Deferred` `D2`, and `D2` must then complete before any further callbacks on `D1` will execute (and later callbacks on `D1` get the *result* of `D2` rather than `D2` itself). So, `D1` might have `called=True` (as in, it has started running its callbacks), but any new callbacks added to `D1` won't get run until `D2` completes - so if you `yield D1` in an `inlineCallbacks` function, your `yield` will 'block'. In conclusion: some of our assumptions in `logcontext` were invalid. We need to make sure that we don't optimise out the logcontext juggling when this situation happens. Fortunately, it is easy to detect by checking `D1.paused`.
erikjohnston
approved these changes
May 2, 2018
tests/util/test_logcontext.py
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| return self._test_preserve_fn(nonblocking_function) | ||
| return self._test_run_in_background(nonblocking_function) | ||
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| @unittest.DEBUG |
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removed the spurious |
neilisfragile
added a commit
that referenced
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May 18, 2018
Changes in synapse v0.29.1 (2018-05-17) ========================================== Changes: * Update docker documentation (PR #3222) Changes in synapse v0.29.0 (2018-05-16) =========================================== Not changes since v0.29.0-rc1 Changes in synapse v0.29.0-rc1 (2018-05-14) =========================================== Notable changes, a docker file for running Synapse (Thanks to @kaiyou!) and a closed spec bug in the Client Server API. Additionally further prep for Python 3 migration. Potentially breaking change: * Make Client-Server API return 401 for invalid token (PR #3161). This changes the Client-server spec to return a 401 error code instead of 403 when the access token is unrecognised. This is the behaviour required by the specification, but some clients may be relying on the old, incorrect behaviour. Thanks to @NotAFile for fixing this. Features: * Add a Dockerfile for synapse (PR #2846) Thanks to @kaiyou! Changes - General: * nuke-room-from-db.sh: added postgresql option and help (PR #2337) Thanks to @rubo77! * Part user from rooms on account deactivate (PR #3201) * Make 'unexpected logging context' into warnings (PR #3007) * Set Server header in SynapseRequest (PR #3208) * remove duplicates from groups tables (PR #3129) * Improve exception handling for background processes (PR #3138) * Add missing consumeErrors to improve exception handling (PR #3139) * reraise exceptions more carefully (PR #3142) * Remove redundant call to preserve_fn (PR #3143) * Trap exceptions thrown within run_in_background (PR #3144) Changes - Refactors: * Refactor /context to reuse pagination storage functions (PR #3193) * Refactor recent events func to use pagination func (PR #3195) * Refactor pagination DB API to return concrete type (PR #3196) * Refactor get_recent_events_for_room return type (PR #3198) * Refactor sync APIs to reuse pagination API (PR #3199) * Remove unused code path from member change DB func (PR #3200) * Refactor request handling wrappers (PR #3203) * transaction_id, destination defined twice (PR #3209) Thanks to @damir-manapov! * Refactor event storage to prepare for changes in state calculations (PR #3141) * Set Server header in SynapseRequest (PR #3208) * Use deferred.addTimeout instead of time_bound_deferred (PR #3127, #3178) * Use run_in_background in preference to preserve_fn (PR #3140) Changes - Python 3 migration: * Construct HMAC as bytes on py3 (PR #3156) Thanks to @NotAFile! * run config tests on py3 (PR #3159) Thanks to @NotAFile! * Open certificate files as bytes (PR #3084) Thanks to @NotAFile! * Open config file in non-bytes mode (PR #3085) Thanks to @NotAFile! * Make event properties raise AttributeError instead (PR #3102) Thanks to @NotAFile! * Use six.moves.urlparse (PR #3108) Thanks to @NotAFile! * Add py3 tests to tox with folders that work (PR #3145) Thanks to @NotAFile! * Don't yield in list comprehensions (PR #3150) Thanks to @NotAFile! * Move more xrange to six (PR #3151) Thanks to @NotAFile! * make imports local (PR #3152) Thanks to @NotAFile! * move httplib import to six (PR #3153) Thanks to @NotAFile! * Replace stringIO imports with six (PR #3154, #3168) Thanks to @NotAFile! * more bytes strings (PR #3155) Thanks to @NotAFile! Bug Fixes: * synapse fails to start under Twisted >= 18.4 (PR #3157) * Fix a class of logcontext leaks (PR #3170) * Fix a couple of logcontext leaks in unit tests (PR #3172) * Fix logcontext leak in media repo (PR #3174) * Escape label values in prometheus metrics (PR #3175, #3186) * Fix 'Unhandled Error' logs with Twisted 18.4 (PR #3182) Thanks to @Half-Shot! * Fix logcontext leaks in rate limiter (PR #3183) * notifications: Convert next_token to string according to the spec (PR #3190) Thanks to @mujx! * nuke-room-from-db.sh: fix deletion from search table (PR #3194) Thanks to @rubo77! * add guard for None on purge_history api (PR #3160) Thanks to @krombel!
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So, it turns out that if you have a first
DeferredD1, you can add a callback which returns anotherDeferredD2, andD2must then complete before any further callbacks onD1will execute (and later callbacks onD1get the result ofD2rather thanD2itself).So,
D1might havecalled=True(as in, it has started running its callbacks), but any new callbacks added toD1won't get run untilD2completes - so if youyield D1in aninlineCallbacksfunction, youryieldwill 'block'.In conclusion: some of our assumptions in
logcontextwere invalid. We need to make sure that we don't optimise out the logcontext juggling when this situation happens. Fortunately, it is easy to detect by checkingD1.paused.