commit 6ffe0ab56793b6764be20377f66d3148e50ce7ec
author Zim <zezeozue@google.com> Mon Oct 09 21:10:30 2023 +0100
committer Zim <zezeozue@google.com> Tue Oct 10 11:33:51 2023 +0100
tree 8508c5a0cb26ec61d12be85bfabae03cc9c00e29
parent a908c7a3e56a876adb553a090851700ca68fa350

[stdlib]: Cache critical path join with thread_states

The current impl of span_join has a limitation that there
must be no overlaps within a partition. This is a challenge when
span joining all critical paths with all thread_states because
multiple threads can share the same critical paths.

This restriction means that the result of querying the critical_path
+ thread_state table for more than one critical path thread at a time
is undefined. This is fine because the exposed APIs don't allow you
do that anyways.

With the introduction of macros, it would be great to expose APIs
to extract the critical path over arbitrary (overlapping) time windows.
This change makes such queries possible on the critical_path
+ thread_state table. The limitation still applies for slices but having
this functionality for thread_states is quite powerful for instance to
extract the critical paths over all monitor contentions in a trace.

There is a performance hit to caching this result but it should speed
up subsequent queries.

Test: tools/diff_test_trace_processor.py out/android/trace_processor_shell --name-filter '.*thread_executing_span.*'
Change-Id: I5a44f91df4d6e08e8ffae4422dc88ad7c3ea4ff8