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 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(). 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_) { // omit some initialize code... // my code begin_papi_thread(&eventSet); // Processing k-means, omit codes. // is_center value will be updated correctly // my code end_papi_thread(&eventSet); // when jumping into this, error happens 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!