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#include <stdio.h>
#include <pthread.h>
#include <sched.h>
#include <string.h>
#include <err.h>
#include "bench.h"
static char name[] = "Mutex Lock/Unlock, Contention";
static char doc[] =
"\tThis is the time interval between when one thread calls\n"
"\tpthread_mutex_unlock() and another thread that was blocked\n"
"\ton pthread_mutex_lock() returns with the lock held.";
/*
The order of locking looks like this:
A B 1 2 3
=============== =============== == == ==
lock(2) A
yield() A
lock(1) A B
lock(3) B A B
yield() B A B
lock(1) Ba A B
-------
unlock(1) a A B
lock(2) a Ab B
^ A Ab B
unlock(2) A b B
lock(3) A b Ba
^ A B Ba
unlock(3) A B a
lock(1) Ab B a
^ Ab B A
unlock(1) b B A
lock(2) b Ba A
^ B Ba A
unlock(2) B a A
lock(3) B a Ab
^ B A Ab
unlock(3) B A b
lock(1) Ba A b
^ Ba A B
-------
unlock(1) a A B
unlock(3) a A
exit
^ A A
unlock(1) A
unlock(2)
exit
In every cycle, there will be 6 transitions and 6 lock/unlock
pairs. So, to compute the transition time, we subtract the
lock/unlock time computed without contention.
*/
static pthread_mutex_t m1, m2, m3;
static bench_t ba, bb;
void *
thread_a(arg)
{
pthread_set_name_np(pthread_self(), "ta");
pthread_mutex_lock(&m2);
sched_yield();
pthread_mutex_lock(&m1);
bench_amortize(&ba, BENCH_LOOPS) {
pthread_mutex_unlock(&m2);
pthread_mutex_lock(&m3);
pthread_mutex_unlock(&m1);
pthread_mutex_lock(&m2);
pthread_mutex_unlock(&m3);
pthread_mutex_lock(&m1);
}
pthread_mutex_unlock(&m1);
pthread_mutex_unlock(&m2);
return (NULL);
}
void *
thread_b(arg)
{
pthread_set_name_np(pthread_self(), "tb");
pthread_mutex_lock(&m1);
pthread_mutex_lock(&m3);
sched_yield();
bench_amortize(&bb, BENCH_LOOPS) {
pthread_mutex_unlock(&m1);
pthread_mutex_lock(&m2);
pthread_mutex_unlock(&m3);
pthread_mutex_lock(&m1);
pthread_mutex_unlock(&m2);
pthread_mutex_lock(&m3);
}
pthread_mutex_unlock(&m1);
pthread_mutex_unlock(&m3);
return (NULL);
}
int
main() {
pthread_t ta, tb;
bench_init(&ba, name, doc, "from unlock to lock inclusive");
bench_init(&bb, NULL, NULL, NULL);
bench_header(&ba);
pthread_mutex_init(&m1, NULL);
pthread_mutex_init(&m2, NULL);
pthread_mutex_init(&m3, NULL);
pthread_create(&ta, NULL, thread_a, NULL);
pthread_create(&tb, NULL, thread_b, NULL);
pthread_join(ta, NULL);
pthread_join(tb, NULL);
ba.divisor = bb.divisor = 6;
bench_report(&ba);
/* bench_report(&bb); */
exit(0);
}
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