iOSでスピンロック ref: http://qiita.com/ykst/items/abab52d496b4ca37a82a

file0.c

#include <libkern/OSAtomic.h>

static volatile OSSpinLock lock = OS_SPINLOCK_INIT;

void spinlock_lock() 
{
    OSSpinLockLock(&lock);
}

void spinlock_unlock() 
{
    OSSpinLockUnlock(&lock);
}

file1.c

#define SPINLOCK(lock) for (int ___do = ({ OSSpinLockLock(&(lock)); 1; }); ___do || ({ OSSpinLockUnlock(&(lock)); 0; }); ___do = 0)

... 
    SPINLOCK(a_lock) {
        do_something();
    }
...