Summary:
The chrome trace viewer requires events within a thread to strictly nest.
So we need to record the lifetime of the Span objects, not the contexts.
But we still want to show the relationship between spans where a context crosses
threads, so do this with flow events (i.e. arrows).
Before: https://photos.app.goo.gl/q4Dd9u9xtelaXk1v1
After: https://photos.app.goo.gl/5RNLmAMLZR3unvY83
(This could stand some further improvement, in particular I think we want a
container span whenever we schedule work on a thread. But that's another patch)
Reviewers: ioeric
Subscribers: klimek, ilya-biryukov, jkorous-apple, cfe-commits
Differential Revision: https://reviews.llvm.org/D43272
llvm-svn: 325220
Summary:
Instead of passing Context explicitly around, we now have a thread-local
Context object `Context::current()` which is an implicit argument to
every function.
Most manipulation of this should use the WithContextValue helper, which
augments the current Context to add a single KV pair, and restores the
old context on destruction.
Advantages are:
- less boilerplate in functions that just propagate contexts
- reading most code doesn't require understanding context at all, and
using context as values in fewer places still
- fewer options to pass the "wrong" context when it changes within a
scope (e.g. when using Span)
- contexts pass through interfaces we can't modify, such as VFS
- propagating contexts across threads was slightly tricky (e.g.
copy vs move, no move-init in lambdas), and is now encapsulated in
the threadpool
Disadvantages are all the usual TLS stuff - hidden magic, and
potential for higher memory usage on threads that don't use the
context. (In practice, it's just one pointer)
Reviewers: ilya-biryukov
Subscribers: klimek, jkorous-apple, ioeric, cfe-commits
Differential Revision: https://reviews.llvm.org/D42517
llvm-svn: 323872
Summary:
This is probably the right behavior for distributed tracers, and makes unpaired
begin-end events impossible without requiring Spans to be bound to a thread.
The API is conceptually clean but syntactically awkward. As discussed offline,
this is basically a naming problem and will go away if (when) we use TLS to
store the current context.
The apparently-unrelated change to onScopeExit are because its move semantics
broken if Func is POD-like since r322838. This is true of function pointers,
and the lambda I use here that captures two pointers only.
I've raised this issue on llvm-dev and will revert this part if we fix it in
some other way.
Reviewers: ilya-biryukov
Subscribers: klimek, jkorous-apple, ioeric, cfe-commits
Differential Revision: https://reviews.llvm.org/D42499
llvm-svn: 323511
Summary:
[clangd] Tracing improvements
Compose JSON using JSONExpr
Allow attaching metadata to spans (and avoid it if tracing is off)
Attach IDs and responses of JSON RPCs to their spans
The downside is that large responses make the trace viewer sluggish.
We should make our responses less huge :-) Or fix trace viewer.
Reviewers: ilya-biryukov
Subscribers: cfe-commits
Differential Revision: https://reviews.llvm.org/D40132
llvm-svn: 318928
Summary:
This lets you visualize clangd's activity on different threads over time,
and understand critical paths of requests and object lifetimes.
The data produced can be visualized in Chrome (at chrome://tracing), or
in a standalone copy of catapult (http://github.com/catapult-project/catapult)
This patch consists of:
- a command line flag "-trace" that causes clangd to emit JSON trace data
- an API (in Trace.h) allowing clangd code to easily add events to the stream
- several initial uses of this API to capture JSON-RPC requests, builds, logs
Example result: https://photos.app.goo.gl/12L9swaz5REGQ1rm1
Caveats:
- JSON serialization is ad-hoc (isn't it everywhere?) so the API is
limited to naming events rather than attaching arbitrary metadata.
I'd like to fix this (I think we could use a JSON-object abstraction).
- The recording is very naive: events are written immediately by
locking a mutex. Contention on the mutex might disturb performance.
- For now it just traces instants or spans on the current thread.
There are other things that make sense to show (cross-thread flows,
non-thread resources such as ASTs). But we have to start somewhere.
Reviewers: ioeric, ilya-biryukov
Subscribers: cfe-commits, mgorny
Differential Revision: https://reviews.llvm.org/D39086
llvm-svn: 317193
Jordan Rose