OSThread::GetCurrentThreadId() is used in many places throughout
the vm, particularly in facilities that are used heavily, such as
SafepointRwLock. The high frequency of invocations means that the
runtime overhead of getting the current thread id has a significant
impact on the overall performance of the vm.
The current Fuchsia implemention of OSThread::GetCurrentThreadId()
makes a syscall to get the koid of the current thread's handle,
resulting in hundreds of nanoseconds of unnecessary overhead per
invocation.
This patch changes to using the thread's handle as the id, which is
guaranteed to be unique for the lifetime of the thread, unless it
is closed prematurely (nothing in the vm does this). This approach
is similar to what MUSL libc (the libc used by Fuchsia) does for
the same purpose and has significant mileage.
Bug: b/182183059
TEST=existing ci test suite; manually deployed into Fuchsia build.
Change-Id: I274a793a823a717c8dd206b396001c6acb897b9a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/193643
Reviewed-by: Chase Latta <chaselatta@google.com>
Commit-Queue: Chase Latta <chaselatta@google.com>
Corey Tabaka
db0fa84d59