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[C++] Multicore coding - Page 5

post #41 of 45
Look into OpenMP... looks like you are over complicating things here.

http://en.wikipedia.org/wiki/OpenMP
post #42 of 45
Thread Starter 
OK, thanks guys. I'll try again in the morning; cricket to watch right now.

Quote:
Originally Posted by C-bro View Post
Edit: The limiting threads to account ranges is a bad idea. Say thread 0 controls account 0-9, and thread 1 controls accounts 10-19. That works fine when you transfer within an account block, but what happens when you need to transfer from 5 to 15? You'll run into a TON of these type of issues if you look into CUDA threading because all work is broken down into blocks similar to what you described.
I'd be limiting the blocks it could transfer to too.

I will look at doing it properly first; I just wanted to know fi I could use this as a backup if I didn't get it.
Edited by zodac - 12/27/10 at 7:12pm
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post #43 of 45
Quote:
Originally Posted by zodac View Post
I read about that somewhere... at least I remember reading about 'locking' in programming and not understanding it properly (like most things ).

I was thinking of working around it by allowing each thread to only access a range of accounts. Hopefully that way no two threads would access the same account.

Or would that not work?
Each account object must have a lock method. Basically, when your worker thread accesses the payer and payee accounts, it sets the locks to its process ID. That means only that PID is allowed to touch the account. Once the worker thread completes the transfer, it unlocks the two accounts.

1) Worker selects random unlocked account.
2) If no unlocked accounts, sleep.
3) If found, lock this account A.
4) Worker reads account balance.
5) If balance is great than zero, find another random unlocked account.
6) If balance is equal or less than zero, unlock A and sleep.
7) If no other unlocked account, unlock A and sleep.
8) If found, lock this account B.
9) Select a random value less than the balance of account A.
10) Subtract value from A
11) Add value to B
12) Print value, account A, account B to log.
13) Unlock B
14) Unlock A

Note, that you must ensure that you release the lock if you cannot proceed or when you complete. Otherwise, you will deadlock.

Quote:
Originally Posted by zodac View Post
I'd be limiting the blocks it could transfer to too.
Range locks won't work. Deadlocks can still occur, but just less often. You need to set explicit locks each account while it is being modified.
Edited by DuckieHo - 12/28/10 at 6:56am
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post #44 of 45
Thread Starter 
Ok, thanks for clearing that up.

I'll start reading and trying some more stuff, then come back when I need some more help. Thank you everyone.
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post #45 of 45
Oh, the account object would store a float and have lock, read, and add methods. If you want to be fancy, you can add an array to store transaction history.
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