1930952 - Add initial implementation for the Atomics.pause proposal

Status: RESOLVED FIXED

(Core :: JavaScript: Standard Library, enhancement)

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1930952 - Part 1: Initial implementation for the Atomics.pause proposal. r=iain!

Use the following instructions to implement Atomics.pause:

1. Target platform is x86 / x86_64:

• Use the pause instruction which is available since Pentium IV.

2. Target platform is ARM32:

• Use the yield hint instruction which is available since ARMv6.

3. Target platform is ARM64:

• Use the isb instruction.
• ARM64 also provides a yield hint instruction, but current CPUs implement it
  as a nop instruction, so implementations in other languages have switched to
  isb, because it more closely matches the delay observed in x86's pause
  instruction.
• See for example core::hint::spin_loop in Rust or Thread.onSpinWait() in Java.

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1930952 - Part 2: Enable test262 tests for Atomics.pause. r=iain!

Comment 3

[André Bargull [:anba]]

Attachment: Bug 1930952 - Part 3: Support encoding "pause" (x86) and "yield" (arm32) instructions. r=iain!

The instructions are used in the next part.

Comment 4

[André Bargull [:anba]]

Attachment: Bug 1930952 - Part 4: Inline Atomics.pause when called with no arguments. r=iain!

Calling Atomics.pause without having inlining support will just lead to
decreased performance due to the overhead for a JS -> C++ call, so provide at
least inlining support when no arguments are passed. Suppporting the iteration
count argument may require CPU-specific tuning, so this is out-of-scope for
now.

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/3a80e137f7f2
Part 1: Initial implementation for the Atomics.pause proposal. r=iain
https://hg.mozilla.org/integration/autoland/rev/b64f6933537d
Part 2: Enable test262 tests for Atomics.pause. r=iain
https://hg.mozilla.org/integration/autoland/rev/65f71c78b93b
Part 3: Support encoding "pause" (x86) and "yield" (arm32) instructions. r=iain
https://hg.mozilla.org/integration/autoland/rev/e299ddd84481
Part 4: Inline Atomics.pause when called with no arguments. r=iain

Comment 6

[Narcis Beleuzu [:NarcisB]]

https://hg.mozilla.org/mozilla-central/rev/3a80e137f7f2
https://hg.mozilla.org/mozilla-central/rev/b64f6933537d
https://hg.mozilla.org/mozilla-central/rev/65f71c78b93b
https://hg.mozilla.org/mozilla-central/rev/e299ddd84481