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Weird pthread performance difference with printf/cout
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Join Date: Feb 2005
Posts: 466
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Hi,
Trying to play with multithreading by taking some of my existing apps and converting them over. In doing so, I noticed a strange phenomenon that I've been able to reproduce in a very simple program.
let's say I create 2 threads. Each thread simply does a for loop from 1 to 1 billion and returns. The program on my (multi cpu) machine takes 2 - 3 seconds. However, if I put a single printf or cout in the thread's loop (let's say I check in the for loop if I'm at 500 million and if so execute the printf), then the same program takes over 25 seconds. This happens regardless of whether I put a mutex or not around the printf.
has anyone seen anything like this?
Winbatch
Trying to play with multithreading by taking some of my existing apps and converting them over. In doing so, I noticed a strange phenomenon that I've been able to reproduce in a very simple program.
let's say I create 2 threads. Each thread simply does a for loop from 1 to 1 billion and returns. The program on my (multi cpu) machine takes 2 - 3 seconds. However, if I put a single printf or cout in the thread's loop (let's say I check in the for loop if I'm at 500 million and if so execute the printf), then the same program takes over 25 seconds. This happens regardless of whether I put a mutex or not around the printf.
has anyone seen anything like this?
Winbatch
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