Make user space streams faster

[ndossche]

Needs more testing, but shows the general idea.

Small PoC bench:

<?php
class MyStream {
    public $context;

    public function stream_open(
        string $path,
        string $mode,
        int $options,
        ?string &$opened_path
    ): bool {
        // debug_print_backtrace();
        return true;
    }

    public function stream_read(int $count): string|false {
        return 'abc';
    }

    public function stream_eof(): bool {
        return false;
    }
}

stream_wrapper_register('my', MyStream::class);

$f = fopen('my://', 'r');
for ($i = 0; $i < 1000000; $i++)
    fread($f, 4096);

On my i7-4790:

  Time (mean ± σ):     135.6 ms ±   3.9 ms    [User: 132.8 ms, System: 2.3 ms]
  Range (min … max):   132.8 ms … 151.6 ms    22 runs
 
  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet system without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.
 
Benchmark 2: ./sapi/cli/php_old x.php
  Time (mean ± σ):     234.3 ms ±   5.7 ms    [User: 231.4 ms, System: 2.2 ms]
  Range (min … max):   229.4 ms … 249.6 ms    12 runs
 
Summary
  ./sapi/cli/php x.php ran
    1.73 ± 0.07 times faster than ./sapi/cli/php_old x.php