Old instrumentation was designed to collect promise creation stack and
promise scheduled stack together. In DevTools for last 6 months we
show only creation stack for promises. We got strong support from users
for new model. Now we can drop support for scheduled stacks and
simplify implementation.
New promise instrumentation is straightforward:
- we send kDebugPromiseThen when promise is created by .then call,
- we send kDebugPromiseCatch when promise is created by .catch call,
- we send kDebugWillHandle before chained callback and kDebugDidHandle
after chained callback,
- and we send separate kDebugAsyncFunctionPromiseCreated for internal
promise inside async await function.
Advantages:
- we reduce amount of captured stacks (we do not capture stack for
promise that constructed not by .then or .catch),
- we can consider async task related to .then and .catch as one shot
since chained callback is executed once,
- on V8 side we can implement required instrumentation using only
promise hooks,
Disadvantage:
- see await-promise test, sometimes scheduled stack was useful since we
add catch handler in native code,
Implementation details:
- on kInit promise hook we need to figure out why promise was created.
We analyze builtin functions until first user defined function on
current stack. If there is kAsyncFunctionPromiseCreate function then
we send kDebugAsyncFunctionPromiseCreated event. If there is
kPromiseThen or kPromiseCatch then only if this function is bottom
builtin function we send corresponded event to inspector. We need it
because Promise.all internally calls .then and in this case we have
Promise.all and Promise.then on stack at the same time and we do not
need to report this internally created promise to inspector.
Bug: chromium:778796
Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I53f47ce8c5c4a9897655c3396c249ea59529ae47
Reviewed-on: https://chromium-review.googlesource.com/765208
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49553}
With recent CLs we always store maximum N async stack traces and when we reach limit we drop half of them.
Current promise collected event requires creating weak handle:
- it takes time,
- it consumes memory.
Since async task id distribution for promises is uniform (each new promise has last_async_task_id + 1 as an id) our hash map is good enough to handle any amount of async task ids, following time of executing 1 000 000 000 of lookups:
- for empty hash map: 1.45 seconds,
- for hash map with one entry: 14.95 seconds
- 1024 entries: 15.03 seconds
- 1024 * 1024 entries: 14.82 seconds
- 1024 * 1024 * 1024: 17.9 seconds
BUG=v8:6189
R=dgozman@chromium.org,yangguo@chromium.org
Review-Url: https://codereview.chromium.org/2819423005
Cr-Commit-Position: refs/heads/master@{#44750}
