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If you have a program, that has many threads that access the same dynamic arrays of data, you need some mutex or CriticalSection. But mutex is slow- it has to enter global memory, and search for a string, specifying your mutex, and you have to wait for all. CriticalSections seem good, but accessing arrays of one million objects, and if you need to put an mutex in each of them, it all turns crap, as Andy Dick says :).
So, the easiest solution is this:

MyObject struct

     IsAccessed db ?

     MyData dd ? ;.....any data you want, you can have the structure as big as you want

MyObject ends





OnNewData proc    me   ; this is pointer to a MyObject structure

mov ebx,me

.while [ebx].MyObject.IsAccessed

     push ebx

     call SwitchToThread ; it is useless to do anything else!

     pop ebx

.endw

mov [ebx].MyObject.IsAccessed,1



;.... do our processing on MyData here







mov ebx,me

mov [ebx].MyObject.IsAccessed,0 ; release the object



call SwitchToThread ; if this procedure is usually called by a low-priority thread, you should do this, to give immediate access to threads that are more important! Otherwise delete this line



ret

OnNewData endp

Yet, you can use only one bit to specify that the data is locked:

MyObject struct

     Status db ?

     MyData dd ? ;.....any data you want, you can have the structure as big as you want

MyObject ends



MY_OBJECT_STATUS_LOCKED equ 128



OnNewData proc    me   ; this is pointer to a MyObject structure

mov ebx,me

.while [ebx].MyObject.Status & MY_OBJECT_STATUS_LOCKED

     push ebx

     call SwitchToThread ; it is useless to do anything else!

     pop ebx

.endw

or [ebx].MyObject.Status,MY_OBJECT_STATUS_LOCKED



;.... do our processing on MyData here







mov ebx,me

xor [ebx].MyObject.Status,MY_OBJECT_STATUS_LOCKED ; release the object



; you can use also:



;-------\

;  and [ebx].MyObject.Status,( -1 - MY_OBJECT_STATUS_LOCKED) 

;-------/



call SwitchToThread 

ret



OnNewData endp

bitRake's algo is not good if the program knows the pointer, and has to save its data. For example, imagine some object that has a dynamic array with 700 objects, and it's being told to save the data into a file. So, xchg will make the program skip some important data. Or if you have a window with custom-drawn and managed windows inside (that do not use win API to work, but are managed by your program). You click with the mouse on this window over the area that is taken from virtual window Head (for instance). The program searches which window is in the Mouse_x::Mouse_y position, willing to send him a message that the mouse is down. The main window has its own array, where the children windows are registered, and if it doesn't find the target window, it does nothing. Imagine if that window is working in the moment the mouse button is pressed and we've deleted the window's pointer (unregister it). Nothing happens. Won't the user hate it?
So, if the data that we have will be saved, we should wait for the object to be released instead of skipping it ;). And with thread priorities set up, we can know which thread will be the first to switch to. I know it not from theory, but from a lot of practise. I've got a huge mainframe created using these mutex of mine, that works perfectly.

How it can happen in 1 processor system if threads have different priorities?

And what about multiprocessor systems? ;)

Gosh, sorry then. /me dumb . very, very dumb.
I guess I've really been lucky.

no! you got the good idea, but I think the code is nothing like that. I think this is it:

@@:

mov al,1

mov ebx,me

xchg al,[ebx].MyObject.IsAccessed

or al,al

jz @F

call SwitchToThread

jmp @B

@@:

(I hope I'm not wrong as usual)

Ultrano, I don't really understand what the SwitchToThread proc does. My little snippet just waits until the object is available before continuing.

SwitchToThread is NT only. what about Sleep(0) ? or are there some consequences my dull mind hasn't picked up?

well, i was thinking whether there's something "bad" about Sleep(0) vs. SwitchToThread() in a situation like this?