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// author: Marc Orr
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#define NUM_TRIES 1000
// Make sure that flags and wait sit in different cache lines
volatile int flags[10];
volatile int wait[10];
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void *DoWork1(void *threadid)
{
flags[0] = flags[0] + 1;
wait[0] = 0;
pthread_exit(0);
}
void *DoWork2(void *threadid)
{
pthread_mutex_lock (&mutex);
flags[0] = flags[0] + 1;
pthread_mutex_unlock (&mutex);
pthread_exit(0);
}
////////////////////////////////////////////////////////////////////////////////
// Program main
////////////////////////////////////////////////////////////////////////////////
int main( int argc, char** argv)
{
// stuff for thread
pthread_t threads[1];
// initialize global variables
flags[0] = 0;
wait[0] = 1;
// monitor (via gcc intrinsic)
__builtin_ia32_monitor ((void *)&flags, 0, 0);
// invalidate flags in this cpu's cache
pthread_create(&threads[0], NULL, DoWork1, NULL);
while (wait[0]);
// launch thread to invalidate address being monitored
pthread_create(&threads[0], NULL, DoWork2, NULL);
// wait for other thread to modify flags
int mwait_cnt = 0;
do {
pthread_mutex_lock (&mutex);
if (flags[0] != 2) {
pthread_mutex_unlock (&mutex);
__builtin_ia32_mwait(0, 0);
} else {
pthread_mutex_unlock (&mutex);
}
mwait_cnt++;
} while (flags[0] != 2 && mwait_cnt < NUM_TRIES);
// test may hang if mwait is not working
if (flags[0]==2) {
printf("mwait regression PASSED, flags[0] = %d\n", flags[0]);
} else {
printf("mwait regression FAILED, flags[0] = %d\n", flags[0]);
}
return 0;
}
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