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Tweak getCurrentContext for SPEED #5959

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merged 1 commit into from Nov 5, 2019

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@headius headius commented Nov 5, 2019

This change reduces the overhead of calling Ruby.getCurrentContext
since we still call it in a number of places.

  • ThreadService now extends ThreadLocal rather than aggregating a ThreadLocal in a field. This eliminates one hop.
  • All hot-path methods in ThreadService are static.
  • Restore @kares recursion logic since it does appear faster than an explicit null check loop.

On OpenJDK 8 C2 this reduces single-thread getCurrentContext time from around 4ns to around 3.2ns. Other VMs have similar gains.

Tested with a trivial benchmark:

import org.jruby.Ruby;

public class ContextGetter {
  public static void main(String[] args) {
    Ruby runtime = Ruby.newInstance();
    while (true) {
      long nanos = System.nanoTime();
      for (int i = 0; i < 100_000_000; i++) {
        runtime.getCurrentContext();
      }
      System.out.println((System.nanoTime() - nanos) / 100_000_000.0);
    }
  }
}

This change reduces the overhead of calling Ruby.getCurrentContext
since we still call it in a number of places.

* ThreadService now extends ThreadLocal rather than aggregating
  a ThreadLocal in a field. This eliminates one hop.
* All hot-path methods in ThreadService are static.
* Restore @kares recursion logic since it does appear faster than
  an explicit null check loop.

On OpenJDK 8 C2 this reduces single-thread getCurrentContext time
from around 4ns to around 3.2ns. Other VMs have similar gains.

Tested with a trivial benchmark:

```java
import org.jruby.Ruby;

public class ContextGetter {
  public static void main(String[] args) {
    Ruby runtime = Ruby.newInstance();
    while (true) {
      long nanos = System.nanoTime();
      for (int i = 0; i < 100_000_000; i++) {
        runtime.getCurrentContext();
      }
      System.out.println((System.nanoTime() - nanos) / 100_000_000.0);
    }
  }
}
```
@headius headius added this to the JRuby 9.2.10.0 milestone Nov 5, 2019
@headius
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headius commented Nov 5, 2019

Assembly output from this benchmark and this branch on OpenJDK8 C2 is here: https://gist.github.com/headius/ac6ae20bcaa33c9795c3df4decb88dfd

Note that the hot path appears to have inlined completely down to line 167, returning the non-null result at that point. This is a Very Good Thing.

@headius headius merged commit bb07dea into jruby:master Nov 5, 2019
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@headius headius deleted the faster_current_context branch Nov 5, 2019
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