I tried this patch with a test where multiple workers are present -- it does
not help. :(
Or is this another problem?
another test attached.
--kcc
--kcc
#include <pthread.h>
#include < stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
// This test is race-free,
// but helgrind 3.3.0 reports a race iff n_workers >= 2.
//
// main worker1,worker2,...,workerN
//
// 1. start(all workers)
// a. read(GLOB)
// /----------b. signal(CV)
// 2. wait(CV) <-----/
// 3. write(GLOB)
static int COND = 0;
static int GLOB = 0;
static pthread_cond_t CV = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t MU = PTHREAD_MUTEX_INITIALIZER;
void *run_pm(void*) {
sleep(2); // we want waiter to get there first
int val = GLOB;
pthread_mutex_lock(&MU);
COND++;
fprintf(stderr, "Signaling: COND: %d; val=%d\n", COND, val);
pthread_cond_signal(&CV);
pthread_mutex_unlock(&MU);
return NULL;
}
int main(int argc, char **argv) {
pthread_t threads[100];
int n_workers = argc == 2 ? atoi(argv[1]) : 2;
for (int i = 0; i < n_workers; i++) {
pthread_create(&threads[i], NULL, run_pm, NULL);
}
bool entered_cond_wait = false;
pthread_mutex_lock(&MU);
while (COND != n_workers) {
entered_cond_wait = true;
printf("Blocking: COND=%d\n", COND);
pthread_cond_wait(&CV, &MU);
printf("Waking: COND=%d\n", COND);
}
pthread_mutex_unlock(&MU);
assert(COND == n_workers); // being paranoid
assert(entered_cond_wait); // because otherwise is unfair
GLOB = 2; // race is reported here
fprintf(stderr, "GLOB: %d\n", GLOB);
for (int i = 0; i < n_workers; i++) {
pthread_join(threads[i], NULL);
}
return 0;
}
On Dec 13, 2007 12:24 PM, Julian Seward <[EMAIL PROTECTED]> wrote:
> On Thursday 13 December 2007 09:07, Konstantin Serebryany wrote:
> > But isn't it expensive?
> >
> > On Dec 13, 2007 11:01 AM, Julian Seward < [EMAIL PROTECTED]> wrote:
> > > On Thursday 13 December 2007 08:44, Konstantin Serebryany wrote:
> > > > Hi,
> > > >
> > > > The same false positive appears when mixing mutexes and semaphores.
> > > > Test attached.
> > > > As with cond vars, we are able to transition Excl(T1)->Excl(T2), but
> > > > can not do ShM(T1,T2)->Excl(T2).
> > > >
> > > > As I understand, fixing this properly will require storing SegmentID
> in
> > >
> > > all
> > >
> > > > shadow words, not only in those that are in Exclusive state.
> > > > This will hardly squeeze into 32 bits though, need 64... :(
> > >
> > > No, I don't think so. We just need to do the same memory ownership
> > > transition for semaphores that the "cvhack" patch does for CVs. I'll
> > > extend the current patch.
>
> Here is version 2 of the cvhack patch. This makes your semaphore test
> run clean (with --happens-before=cvhack).
>
> J
>
>
>
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <assert.h>
// This test is race-free,
// but helgrind 3.3.0 reports a race iff n_workers >= 2.
//
// main worker1,worker2,...,workerN
//
// 1. start(all workers)
// a. read(GLOB)
// /----------b. signal(CV)
// 2. wait(CV) <-----/
// 3. write(GLOB)
static int COND = 0;
static int GLOB = 0;
static pthread_cond_t CV = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t MU = PTHREAD_MUTEX_INITIALIZER;
void *run_pm(void*) {
sleep(2); // we want waiter to get there first
int val = GLOB;
pthread_mutex_lock(&MU);
COND++;
fprintf(stderr, "Signaling: COND: %d; val=%d\n", COND, val);
pthread_cond_signal(&CV);
pthread_mutex_unlock(&MU);
return NULL;
}
int main(int argc, char **argv) {
pthread_t threads[100];
int n_workers = argc == 2 ? atoi(argv[1]) : 2;
for (int i = 0; i < n_workers; i++) {
pthread_create(&threads[i], NULL, run_pm, NULL);
}
bool entered_cond_wait = false;
pthread_mutex_lock(&MU);
while (COND != n_workers) {
entered_cond_wait = true;
printf("Blocking: COND=%d\n", COND);
pthread_cond_wait(&CV, &MU);
printf("Waking: COND=%d\n", COND);
}
pthread_mutex_unlock(&MU);
assert(COND == n_workers); // being paranoid
assert(entered_cond_wait); // because otherwise is unfair
GLOB = 2; // race is reported here
fprintf(stderr, "GLOB: %d\n", GLOB);
for (int i = 0; i < n_workers; i++) {
pthread_join(threads[i], NULL);
}
return 0;
}
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