New to pthread programming, and stuck on this error when working on a C++&C mixed code.
What I have done is to call the c code in the thread created by the c++ code. There is a static boolean pointer is_center used in the thread and should got free when the thread finishes.
However I noticed that every time when the program processed into the c function, the value of the boolean pointer would be changed and the segmentation fault then happened due to the free(). And the problem only happens when the c code is used. Remove the c code and the multi-thread c++ part works well.
Detail code is as follows:
static bool *is_center;
// omit other codes in between ...
void streamCluster( PStream* stream)
{
// some code here ...
while(1){
// some code here ...
is_center = (bool*)calloc(points.num,sizeof(bool));
// start the parallel thread here.
// the c code is invoked in this function.
localSearch(&points,kmin, kmax,&kfinal); // parallel
free(is_center);
}
And the function using parallel is as follows (my c code is invoked in each thread):
void localSearch( Points* points, long kmin, long kmax, long* kfinal ) {
pthread_barrier_t barrier;
pthread_t* threads = new pthread_t[nproc];
pkmedian_arg_t* arg = new pkmedian_arg_t[nproc];
pthread_barrier_init(&barrier,NULL,nproc);
for( int i = 0; i < nproc; i++ ) {
arg[i].points = points;
arg[i].kmin = kmin;
arg[i].kmax = kmax;
arg[i].pid = i;
arg[i].kfinal = kfinal;
arg[i].barrier = &barrier;
pthread_create(threads+i,NULL,localSearchSub,(void*)&arg[i]);
}
for ( int i = 0; i < nproc; i++) {
pthread_join(threads[i],NULL);
}
delete[] threads;
delete[] arg;
pthread_barrier_destroy(&barrier);
}
Finally the function calling my c code:
void* localSearchSub(void* arg_) {
int eventSet = PAPI_NULL;
begin_papi_thread(&eventSet);
pkmedian_arg_t* arg= (pkmedian_arg_t*)arg_;
pkmedian(arg->points,arg->kmin,arg->kmax,arg->kfinal,arg->pid,arg->barrier);
end_papi_thread(&eventSet);
return NULL;
}
And from gdb, what I have got for the is_center is:
Breakpoint 2, localSearchSub (arg_=0x600000000000bc40) at streamcluster.cpp:1711
1711 end_papi_thread(&eventSet);
(gdb) s
Hardware watchpoint 1: is_center
Old value = (bool *) 0x600000000000bba0
New value = (bool *) 0xa93f3
0x400000000000d8d1 in localSearchSub (arg_=0x600000000000bc40) at streamcluster.cpp:1711
1711 end_papi_thread(&eventSet);
Any suggestions? Thanks in advance!
Some new information about the code: for the c code, I am using the PAPI package. I write my own papi wrapper to initialize and read system counters. The code is as follows:
void begin_papi_thread(int* eventSet)
{
int thread_id = pthread_self();
// Events
if (PAPI_create_eventset(eventSet)) {
PAPI_perror(return_value, error_string, PAPI_MAX_STR_LEN);
printf("*** ERROR *** Failed to create event set for thread %d: %s\n.", thread_id, error_string);
}
if((return_value = PAPI_add_events(*eventSet, event_code, event_num)) != PAPI_OK)
{
printf("*** ERROR *** Failed to add event for thread %d: %d.\n", thread_id, return_value);
}
// Start counting
if ((return_value = PAPI_start(*eventSet)) != PAPI_OK) {
PAPI_perror(return_value, error_string, PAPI_MAX_STR_LEN);
printf("*** ERROR *** PAPI failed to start the event for thread %d: %s.\n", thread_id, error_string);
}
}
void end_papi_thread(int* eventSet)
{
int thread_id = pthread_self();
int i;
long long * count_values = (long long*)malloc(sizeof(long long) * event_num);
if (PAPI_read(*eventSet, count_values) != PAPI_OK)
printf("*** ERROR *** Failed to load count values.\n");
if (PAPI_stop(*eventSet, &dummy_values) != PAPI_OK) {
PAPI_perror(return_value, error_string, PAPI_MAX_STR_LEN);
printf("*** ERROR *** PAPI failed to stop the event for thread %d: %s.\n", thread_id, error_string);
return;
}
if(PAPI_cleanup_eventset(*eventSet) != PAPI_OK)
printf("*** ERROR *** Clean up failed for the thread %d.\n", thread_id);
}