Re: mt questions

[Vladimir T. <vtz...@gm...>]

> 1.  Is test-and-set faster than compare-and-swap?
testandset in xthread.d is special case of cas with 0/1 values.


> 2.  In [xthread.d, line 104 ]  its mentioned "raw mutex used for thread
> suspension/resume". What does a raw mutex refer to here? Is it any
> different from a normal mutex? Does by raw mutex you mean .. simply
> a mutex (! mutex/condition variable pair) ?

In all comments "raw" mutex means operating system mutex while "mutex"
means lisp object mutex (see lispbibl.d:6831).
"raw" mutex is used for lisp mutex implementation.

> 3.  I came across futex. It's a kernel facility the enables fast
> implementations
> of mutex in userspace and is used to implement basic locking. Why don't we
> incorporate it in achieving locking ? since Pthread Mutex in the latest
> Linux
> distributions are implemented through Futex logic.

futex is linux only thing. clisp runs on bsd, win32, etc. Also futex
cannot be used with condition variables.

> 4.  In [xthread.d, line 52 ] I could not understand the 'Create a new
> thread'
> method's  void* (*startroutine)(void*) argument. Please, also provide me
> with a definition of startroutine.

See zthread.d:228
This is start routine for all threads created from lisp code.

> 5.  In [xthread.d, line 99,152] what does #define THREADPROC_SIGNATURE do?
This is just a syntax sugar to hide win32/posix thread function return type.

> 6.  In [xthread.d, line 156],  its mentioned 'an inefficient implementation
> of
> condition variable for win32.'. Why don't we use windows 'Events' instead of
> a condition variable, since I read they are like a mutex/condition pair
> wrapped
> around a boolean.
> plus there's also a to-do marked there-  "TODO : make it better."

Condition variable emulation on win32 is not exactly inefficient but
is not fair for sure. Win32 event is very different compared to posix
condition variables - please go over related docs again.
Recent win32 versions (not sure from when exactly) have real condition
variables (http://msdn.microsoft.com/en-us/library/windows/desktop/ms682052(v=vs.85).aspx).
The reason we do not use them is that we want to support windows xp as
well. Of course some ifdefs are possible but nobody bothered yet.