[MUD-Dev] (no subject)

claw at kanga.nu claw at kanga.nu
Sun Dec 23 23:41:34 New Zealand Daylight Time 2001


>From shren at fnord.io.com  Fri Apr 27 23: 08:29 2001
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Date: Sat, 28 Apr 2001 01:08:22 -0500 (CDT)
From: shren <shren at io.com>
To: mud-dev at kanga.nu
Subject: Re: [MUD-Dev] Re: TECH: Distributed Muds 
In-Reply-To: <30426.988420819 at 2wire.com>
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Resent-To: mud-dev at kanga.nu
Resent-Date: Sun, 23 Dec 2001 23:41:34 -0800
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Resent-From: J C Lawrence <claw at kanga.nu>

<EdNote: This is an old message that Mailman somehow diverted
without my noticing>

On Fri, 27 Apr 2001, J C Lawrence wrote:
> On Fri, 27 Apr 2001 12:57:43 -0400 
> Derek Snider <derek at idirect.com> wrote:

>> Threaded/multi-process MUDs are a completely different story.
>> It's like comparing apples and oranges.
 
> Given a threaded IO setup with only two threads (IO gathering and
> game process), the delta really isn't that large.

I concurr.  Designing entire architectures that have 30,000 threads
dancing in harmony is very, very tricky.  But threading is very
useful when you are making a thread to solve a reasonably
modularized problem that has to happen (or would be better
happening) independantly from the rest of execution.

The classic example is sound.  If you're writing some code that
deals with sound buffers directly, then you can either check the
sound buffers constantly in your code, to make sure your 2 second
sound buffer stays full with new sound, or you can push it off in a
seperate thread.  (I'd swear that Ultima 9 had sound in the main
thread.  I'm not *certain*, but the way things would skip sometimes,
it seemed very likely.)

I find the key to working with threads is state diagrams.  Your
threads have to clearly be in one state or another, to make a
coherent design.

Since I've recently been told that long posts are ok, I'll dump some
code here that I wrote to do simple interaction with threads.  I'm
not saying it's the best code, but I get by with it.  (Actually, I'm
not even sure this is the best version of my code.)

Note : this is windows code, but the principles are similar in the
UNIX world.

This is far from the best code you'll find.  Books big enough to do
mugging in Central Park are introductions to the subject.  The
reason I think it will be interesting for those who don't know
threads is that it is the smallest modular implementation of
threading I could come up with.  We never launched a project that
*uses* this code, however, so I can't guarantee stability.  It
served, however, all the way up to the point where we realized that
our product would draw lawsuits like flies and abandoned it.  I look
back now and see some things I'd change, but all code is like that.

I've got some other thread code that is object based, developed from
this code, where you can make an object have it's own thread by
having it inherit the "runnable" class, but I think this older code
is better for a c sample, as it abuses the c++ class structure for
it's advantages to essentially write c style code.

Here's how you might use this code.  As for communicating between
the thread and the outside world, the best thing to do is to make
your favorite queue class threadsafe and then put instances of it
inside y, below.  Since the queues are threadsafe, the thread can
push things onto them and you can pop things outside outside of the
thread.

Below, three functions are declared.  Init, loop, and end.  These
functions are passed as pointers to the object.  The first is run
once.  The second is run as a loop when hGo is set.  The third is
triggered when CThread goes out of scope (x is deleted).

    CThread *x;
    
    void init(void *) {//this function is run once at the beginning}
    void loop(void *) {//this function is run as the main loop}
    void end(void *) {//this function is run at the end}
    struct something y; 
     
    x = new CThread("blah", // an arbitrary (should be unique) thread name
                    &y,     // this pointer is passed to init, loop, and end
                    init,loop,end  // function pointers
                    );
    
    //init(y) is run in the thread at this point
    
    // tell it to start - these three statements should be a method of
    // CThread and *not* accessed externally.  Thing one I'd change -
    // making a start method and a stop method inside the class.
    // Exercise to the reader, and all that.
    HANDLE hGo;
    OpenEvent(NULL,FALSE,"blah_go");
    SetEvent(hGo);
    
    //do other stuff here.  while you do,
    //loop(y) is run repeatedly untill....
    
    delete x;
    
    //loop(y) finishes if it is currently running.
    //end(y) is run.
    
    //here's the 4 source files.
    /* Thread.h begin */
    
    #include "stdafx.h"
    #include "threadproc.h"
    
    #ifndef _thread_class_h_
    #define _thread_class_h_
    
    unsigned __stdcall threadproc(void *lpThreadParameter);
    
    class CThread  
    {
    friend unsigned __stdcall threadproc(void *lpThreadParameter);
    
    protected:
    	HANDLE hIdle,hEnd,hEndAck,hChild;
    	HANDLE hGo;
    	char szIdle[16],szEnd[16],szEndAck[16];
    	char szWait[16];
    	unsigned int id;
    	void *pass;
    	void (*start)(void *);
    	void (*loop)(void *);
    	void (*end)(void *);
    
    	struct threadinfo ti;
    
    public:
    	CThread();
    	CThread(char *name, void *data, 
                    void(*a)(void *),void(*b)(void *),void(*c)(void *));
    	virtual ~CThread();
    };
    
    #endif
    
    /* Thread.h end */
    /* Threadproc.h begin */
    
    #ifndef _threadproc_h_
    #define _threadproc_h_
    
    unsigned int __stdcall threadproc(void *x);
    
    struct threadinfo {
    	char szIdle[16];
    	char szEnd[16];
    	char szEndAck[16];
    	char szGo[16];
    	void (*start)(void *);
    	void (*loop)(void *);
    	void (*end)(void *);
    	void *data;
    };
    
    #endif
    
    /* Threadproc.h end */
    /* Thread.cpp begin */
    
    #include "stdafx.h"
    #include "Thread.h"
    #include "threadproc.h"
    
    CThread::CThread()
    {
    }
    
    CThread::CThread(char *name, void *data, void(*a)(void *),
                     void(*b)(void *),void(*c)(void *))
    {
    	ODS("thread constructor\n");
    	pass = data;
    
    // store the function pointers and the data pointer.
    	ti.start = a;
    	ti.loop = b;
    	ti.end = c;
    	ti.data = data;
    
    // create the event names.
    	sprintf(ti.szIdle,"%s_idle",name);
    	sprintf(ti.szEnd,"%s_end",name);
    	sprintf(ti.szEndAck,"%s_end_ack",name);
    	sprintf(ti.szGo,"%s_go",name);
    
    // create the thread running threadproc()
    	hChild = (HANDLE)( 
        _beginthreadex(NULL,0,threadproc,(void *)&ti,CREATE_SUSPENDED,&id)
            );
    
    // events
    
    // this indicates that the thread is idle when set.
    // if you want to modify the data outside the class,
    // then you can, outside the class, Reset the go
    // event then wait for the Idle event. 
    	hIdle = CreateEvent(0,TRUE,FALSE,ti.szIdle);  
            ResetEvent(hIdle);
    // end and endack are used for synchronous shutdown
    	hEnd = CreateEvent(0,TRUE,FALSE,ti.szEnd);	
            ResetEvent(hEnd);
    	hEndAck = CreateEvent(0,TRUE,FALSE,ti.szEndAck);	
            ResetEvent(hEndAck);
    // to execute the loop or not execute the loop?
    	hGo = CreateEvent(0,TRUE,FALSE,ti.szGo);	
            ResetEvent(hGo);
    
    // make the thread start
    	ResumeThread(hChild);
    }
    
    CThread::~CThread()
    {
    	ODS("destructor\n");
    	WaitForSingleObject(hIdle,INFINITE);
    	ODS("thread is idle\n");
    	SetEvent(hEnd);
    	WaitForSingleObject(hEndAck,INFINITE);
    	ODS("thread is terminated\n");
    }
    
    /* Thread.cpp end */
    
    /* Threadproc.cpp begin */
    
    #include "stdafx.h"
    #include "Thread.h"
    #include "threadproc.h"
    
    unsigned int __stdcall threadproc(void *in)
    {
    	HANDLE hIdle, hEnd, hEndAck, hGo;
    	HRESULT hr;
    	struct threadinfo *pass;
    
    	pass = (struct threadinfo *)in;
    
    // open copies of the events made inside the class.
    	hIdle = OpenEvent(EVENT_MODIFY_STATE,FALSE,pass->szIdle);
    	if (hIdle == 0) {ODS("dead idle handle!\n");}
    	hEnd = OpenEvent(EVENT_MODIFY_STATE,FALSE,pass->szEnd);
    	if (hEnd == 0) {ODS("dead end handle!\n");}
    	hEndAck = OpenEvent(EVENT_MODIFY_STATE,FALSE,pass->szEndAck);
    	if (hEndAck == 0) {ODS("dead endack handle!\n");}
    	hGo = OpenEvent(EVENT_MODIFY_STATE,FALSE,pass->szGo);
    	if (hGo == 0) {ODS("dead wait handle!\n");}
    
    // run the start function the user passed us
    	pass->start(pass->data);
    	while (0==0)
    	{
    // if we can go, run the main loop once
    		hr = WaitForSingleObject(hGo,0);
    		if (hr == WAIT_OBJECT_0)
    		{
    			pass->loop(pass->data);
    		}
    // we are idle
    		SetEvent(hIdle);
    // let the other processes have some time
    		Sleep(0);
    // check if we've been instructed to terminate
    		hr = WaitForSingleObject(hEnd,0);
    		if (hr == WAIT_OBJECT_0)
    		{
    			SetEvent(hEndAck);
    			pass->end(pass->data);
    			_endthreadex(0);
    		}
    // we are no longer idle
    		ResetEvent(hIdle);
    	}
        
    	return 0;
    }
    
    /* Threadproc.cpp end */
    
    
--
Give a man a fish, and you feed him for a day.
Teach a man to fish, and you've created competition.
Competition keeps you on your toes.
    
    
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