[ruby-core:116347] [Ruby master Bug#20197] Postponed job invocations are significantly reduced in Ruby 3.3

["osyoyu (Daisuke Aritomo) via ruby-core" <ruby-core@ml.ruby-lang.org>]

Issue #20197 has been reported by osyoyu (Daisuke Aritomo).

----------------------------------------
Bug #20197: Postponed job invocations are significantly reduced in Ruby 3.3
https://bugs.ruby-lang.org/issues/20197

* Author: osyoyu (Daisuke Aritomo)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.3.0 (2023-12-25 revision 5124f9ac75) [x86_64-linux]
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN
----------------------------------------
The number of postponed job invocations has been significantly reduced in Ruby 3.3.
While my understanding is that postponed jobs provide no guarantee of how soon registered callbacks will fire, I believe the current rate is too low for practical usage, especially for profilers such as StackProf.

A git bisect led me to https://github.com/ruby/ruby/commit/1f0304218cf00e05a4a126196676ba221ebf91f6 which obviously seems to be related, but I'm not sure why.

## Repro

### Expected

The job fires (nearly) every 100 ms.

```
% ruby bin/test.rb # runs for 3 seconds
count: 1
count: 2
(snip)
count: 29
```

### Actual

The job fires only once.

```
% ruby bin/test.rb
count: 1
count: 2
(snip)
count: 29
```

### Code

```ruby
require 'mycext'

time = Time.now
th = Thread.new do
  loop do
    sleep 0.01
    break if Time.now - time > 3 # run for 3 seconds
  end
end
th.join
```

```c
#include <pthread.h>
#include <stdio.h>
#include <time.h>

#include "ruby.h"
#include "ruby/debug.h"

int called_count;

void
postponed_job(void *ptr)
{
  called_count++;
  printf("count: %d\n", called_count);
}

_Noreturn void *
pthread_main(void *_)
{
  while (1) {
    rb_postponed_job_register_one(0, postponed_job, NULL);

    // Sleep for 100 ms
    struct timespec ts;
    ts.tv_sec = 0;
    ts.tv_nsec = 100 * 1000 * 1000;
    nanosleep(&ts, NULL);
  }
}

RUBY_FUNC_EXPORTED void
Init_mycext(void)
{
  called_count = 0;

  pthread_t pthread;
  pthread_create(&pthread, NULL, pthread_main, NULL);
}
```



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