Is this method of protecting shared data reasonable?

[htirwin]

I'm re-factoring a program I started when I was much less experienced. I used a simple method to "lock" some data which is shared between two threads; something along these lines.

volatile bool lock;
bool isLocked();
void lock();
void unlock();

//thread1
while(islocked()) usleep(1);
lock();
writeArr(arr);
unlock();

//thread2
while(islocked()) usleep(1);
lock();
readArr(arr);
unlock();

Without the "lock" there are problems. But with it I can't seam to cause any undesired behavior.

What's wrong with this method? What can go wrong?

[cire]

Both threads call lock at the same time and simultaneously write and read the data?

[htirwin]

I just realized I should just use std::atomic <bool>.

std::atomic <bool> lock;

while (lock.exchange(true)) {}
//do stuff
lock = false;

http://www.drdobbs.com/parallel/measuring-parallel-performance-optimizin/212201163?pgno=3