Mutexes and locking

[alexhairyman]

On Monday, 3 March 2014 at 07:38:05 UTC, Ali Çehreli wrote:
> On 03/02/2014 10:38 PM, alexhairyman wrote:
>
> > I think I'm missing something big, but I'm having troubles
> with mutexes
> > (using in a parallel foreach loop somewhere else); Why do the
> trylocks
> > return true shouldn't they return false because the mutex is
> already
> > locked?
>
> The documentation says that Mutex is a recursive lock, meaning 
> that the holder of the lock can lock it even further. :) There 
> is an internal reference count so that the lock must be 
> unlocked the equal number of times that it has been locked.

Oh okay, that makes sense.

>
> > I don't think this is a phobos bug, I'm on OSX using dmd 2.065
> >
> > import core.sync.mutex;
> > import std.stdio;
> >
> > void main()
> > {
> >    Mutex m = new Mutex;
> >    m.lock();
> >    writefln("%s", m.tryLock());
> >    writefln("%s", m.tryLock());
>
> The lock count is now 3. You must unlock it 3 times so that 
> another thread can lock it.
>
> >    return;
> > }
> >
> > produces:
> > true
> > true
> >
> > Thanks!
> >    Alex
>
> Ali

Okay, so when doing something like this

Mutex hashlock;
void tdigest(string path)
{
   MD5Digest thasher = new MD5Digest;
   thasher.put(read(path)); //read the path in to the MD5 API
   hashlock.lock();
   hashkey[path] = thasher.finish();
   hashlock.unlock();
}
void main()
{
   hashlock = new Mutex();
... other stuff
   foreach(string s ; tp.parallel(array of strings))
   {
     tdigest(s);
   }
... even more stuff
}

it will fail because the parallel foreach uses the main thread is 
being used which does some funky stuff? I'm trying to figure out 
how to implement this (for reference I'm just trying to create a 
big hash map of files and their md5's)