617198 - Thread-safe, thread-aware Profiler

Status: RESOLVED WONTFIX

(Tamarin Graveyard :: Profiler, defect)

Description

[Simon Wilkinson]

The current profiling infrastructure assumes single-threaded execution through all sampling locations.

With the asymmetric GC, background compilation, and async XML parsing, this is no longer true.

Two solutions are required:
1) Make the profiler thread-safe
2) Make the profiler's bookkeeping thread-aware

The first of these can be easily achieved by disallowing background threads entry to the profiler. But in that case, the profiler may give misleading information (e.g. 0% time compiling on the main thread? Zero XML objects created in a XML-heavy application that that use XMLAsync?)
Thread-safety could also be gained through serialization of threads around sampling locations, but this also prompts questions of profiler accuracy and Heisenburg effects, i.e. is thread identity accounted for?
Hence, the profiler needs to be made thread-safe, thread-aware, and extended with relevant APIs.

Note that in the current patches for the threading features listed above, in all but one case, background threads are not allowed access to the profiler. The exception is sampling of the incremental marking GC phase; background threads perform this task within a safepoint, so we are assured profiler thread-safety.

Comment 1

[Simon Wilkinson]

Attachment: Initial Patch. MQ rev 197

This patch is really the bare minimum.
Sampling is made thread-safe by disallowing sampling of VM-threads.

Comment 2

[Andre Kruetzfeldt]

Who is to review this one?

Comment 3

[Simon Wilkinson]

(In reply to comment #2)
> Who is to review this one?

treilly I presume.

Comment 4

[Sylvestre Ledru [:Sylvestre]]

Tamarin is a dead project now. Mass WONTFIX.

Comment 5

[Sylvestre Ledru [:Sylvestre]]

Tamarin isn't maintained anymore. WONTFIX remaining bugs.