From: Kirk Haines <wyhaines@...>
Date: 2011-06-28T03:20:10+09:00
Subject: Re: Understanding Threading...

On Mon, Jun 27, 2011 at 12:06 PM, Darryl L. Pierce <mcpierce@gmail.com> wrote:
> On Tue, Jun 28, 2011 at 02:28:07AM +0900, Luiz Angelo Daros de Luca wrote:
>> Is your block using some C extension?

>> In ruby<1.9, threads in ruby do
>> not use system threads. So, if you call
>> some external C command, no thread will run in ruby. In ruby>=1.9, it
>> uses pthreads.
>
> So in 1.9 we should have _some_ semblance of multi-threading with
> extensions?

Yes, if you write your extension to take advantage of it.  Do some
searches for information on rb_thread_blocking_region(), and take a
look at the source code for it in thread.c.  Here are the relevant
comments:

/*
 * rb_thread_blocking_region - permit concurrent/parallel execution.
 *
 * This function does:
 *   (1) release GVL.
 *       Other Ruby threads may run in parallel.
 *   (2) call func with data1.
 *   (3) aquire GVL.
 *       Other Ruby threads can not run in parallel any more.
 *
 *   If another thread interrupts this thread (Thread#kill, signal deliverly,
 *   VM-shutdown request, and so on), `ubf()' is called (`ubf()' means
 *   "un-blocking function").  `ubf()' should interrupt `func()' execution.
 *
 *   There are built-in ubfs and you can specify these ubfs.
 *   However, we can not guarantee our built-in ubfs interrupt
 *   your `func()' correctly.  Be careful to use rb_thread_blocking_region().
 *
 *     * RUBY_UBF_IO: ubf for IO operation
 *     * RUBY_UBF_PROCESS: ubf for process operation
 *
 *   NOTE: You can not execute most of Ruby C API and touch Ruby objects
 *         in `func()' and `ubf()' because current thread doesn't acquire
 *         GVL (cause synchronization problem).  If you need to do it,
 *         read source code of C APIs and confirm by yourself.
 *
 *   NOTE: In short, this API is difficult to use safely.  I recommend you
 *         use other ways if you have.  We lack experiences to use this API.
 *         Please report your problem related on it.
 *
 *   Safe C API:
 *     * rb_thread_interrupted() - check interrupt flag
 *     * ruby_xalloc(), ruby_xrealloc(), ruby_xfree() -
 *         if they called without GVL, acquire GVL automatically.
 */


Kirk Haines
Software Engineer
Engine Yard