Archief - C++: weirdest problem ever

blackrabbit · 14 apr 2010

Gegeven de volgende functie die door een pThread wordt uitgevoerd:

Code:

void *SpeManager::spe_instructions_pthread_function(void * arg)
{
//init some variables
//...
	printf("Running SPE mailbox checker for SPE %u\n",spe.id);
	SpeManager* speManager=(SpeManager*)(args->speManager);
	speInstructionQueue* q = speManager->getSpeQueue(spe);
//...
	
	unsigned int *instructions;
	printf("----- SPE-MANAGER check 1: %u\n",speManager->check());
	while(true)
	{
		//printf(".");//DEZE HIER
		if(q->size()!=0)
		{
			printf("Size is now: %i\n",q->size());
			SPE_instruction instr = q->front();
			//remove from queue
			q->pop();
			//process
			switch(instr.arg_count)
			{
			case 0:
				//do stuff
			break;
			
			case 1:
				//do stuff
			break;
			
			case 2:
				//do stuff
			break;
			
			case 3:
				//do stuff
			break;
			
			default:
				printf("def\n");
				//do other stuff
			break;
			}
			while(!speManager->SPE_mailbox_empty(spe))
			{
				//do nothing (busy wait)
				printf("not empty (SPE %i)\n",spe.id);
			}
			if(size!=0)
			{
				printf("Sending to mailbox of spe %i, size %i\n",spe.id,size);
				delete instructions;
			}
		}
		//printf(",");
	}
	return NULL;
}

Uitvoer van het programma:

Code:

[bartmaes@soft30 t2]$ ./t1
Creating new SpeManager with 1 SPE cores
[B]Running SPE mailbox checker for SPE 0[/B]
[B]----- SPE-MANAGER check 1: 951357[/B]
Running SPE program for SPE 0
(SPE) SPE STARTED
Required number of buffers: 2
Queue-size: 2
(PPU) SPE_instruct(0,1,0xffb09700,64)
(PPU) enqueued instruction: 5 with id 4
(PPU) double check: 5
(PPU) Enqueuing instruction 5 for SPE 0, queue now has size 1
(PPU) SPE_instruct(0,1,0xffb09800,64)
(PPU) enqueued instruction: 9 with id 8
(PPU) double check: 9
(PPU) Enqueuing instruction 9 for SPE 0, queue now has size 2

Als nu in bovenstaande code die 'prinf(".");' uit commentaar wordt gehaald, veranderd de uitvoer naar dit:

Code:

Creating new SpeManager with 1 SPE cores
[B]Running SPE mailbox checker for SPE 0[/B]
[B]----- SPE-MANAGER check 1: 951357[/B]
............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
................................
Running SPE program for SPE 0
............................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
(SPE) SPE STARTED
........................................................................................................................................................
Required number of buffers: 2
Queue-size: 2
(PPU) SPE_instruct(0,1,0xffcad700,64)
(PPU) enqueued instruction: 5 with id 4
.(PPU) double check: 5
..(PPU) Enqueuing instruction 5 for SPE 0, queue now has size 1
(PPU) SPE_instruct(0,1,0xffcad800,64)
(PPU) enqueued instruction: 9 with id 8
(PPU) double check: 9
Size is now: 1
(PPU) Enqueuing instruction 9 for SPE 0, queue now has size 2
Found enqueued instruction for SPE 0
Sending to mailbox of spe 0, size 3
.Size is now: 1
Found enqueued instruction for SPE 0
[B]SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)[/B]
[B](SPE) Fetching instruction
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)[/B]
[B](SPE) original instruction: 5, filtered instr: 1, mask: 3
SPE-inbox not empty (SPE 0)
SPE-inbox not empty (SPE 0)
instruction from mbox: 5, filtered: 1
SPE-inbox not empty (SPE 0)
(SPE) instruction_instr: 1 SPE-inbox not empty (SPE 0)
 blockAdress: 0xffcad700,size 64
Sending to mailbox of spe 0, size 3[/B]
INFO: fetched instruction: 5
...............................................................................................
(SPE) original instruction: 5, filtered instr: 1, mask: 3
......................................................................
(SPE) original instruction: 5, filtered instr: 1, mask: 3
.....................................................................
(SPE) original instruction: 5, filtered instr: 1, mask: 3
.....................................................................
(SPE) original instruction: 5, filtered instr: 1, mask: 3
...........................................................................
(SPE) (successfully fetched correct instruction from mailbox, instruction enqueued for processing) INFO: id: 1, instr: 1
......................................................
(SPE) Fetching instruction
........................................................................................
(SPE) original instruction: 9, filtered instr: 1, mask: 3
................................................................
instruction from mbox: 9, filtered: 1
.............................................................
(SPE) instruction_instr: 1 
................................................................ 
blockAdress: 0xffcad800,size 64
.............................................................
INFO: fetched instruction: 9
.....................................................................
(SPE) original instruction: 9, filtered instr: 1, mask: 3
......................................................................
(SPE) original instruction: 9, filtered instr: 1, mask: 3
......................................................................
(SPE) original instruction: 9, filtered instr: 1, mask: 3
......................................................................
(SPE) original instruction: 9, filtered instr: 1, mask: 3
.........................................................................
(SPE) (successfully fetched correct instruction from mailbox, instruction enqueued for processing) INFO: id: 1, instr: 1
........................................................

Er wordt nu duidelijk méér code uitgevoerd, maar de vraag is: waarom? Die printf zou er toch niet mogen toe doen??

blackrabbit · 15 apr 2010

Code:

		else
		{
			pthread_yield();
		}

Did the trick. Had al langer een vermoeden dat het te maken had met die multi-threading & de busy-waits, maar vond dat ook wel raar: zelfs na héél lang wachten ging het programma niet verder.

Maar veronderstelde dus dat printf de CPU wat 'stalde' en daardoor alles werkte zoals het hoort.

Enfin, dit lijkt het probleem op te lossen, maar blijf het bizar vinden dat thread-sheduling dit probleem niet vanzelf oplost...

FrostByte · 15 apr 2010

Threading is altijd een raar beestje. Helaas kan ik je niet meer zeggen dan dat want ik ben niet zo thuis in C++. Ik ben één van die verwende .NET-ers

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Archief - C++: weirdest problem ever

blackrabbit

Legacy Member

blackrabbit

Legacy Member

FrostByte

Legacy Member