c - inter processes shared memory and pthread_barrier: how to be safe? -

i wanted simple solution inter processes barrier. here solution: solution

but totally lost mmap... first try, fails 1 out of ten times (segfault or deadlock).

i understand problem comes synchronization issue, can't find it. found example set mmaped memory (example), not sure mmaped pthread_barrier.

here extract of code:

#define mmap_file "/tmp/mmapped_bigdft.bin"  void init_barrier() {   pthread_barrier_t *shared_mem_barrier;   pthread_barrierattr_t barattr;   pthread_barrierattr_setpshared(&barattr, pthread_process_shared);    hbcast_fd = open(mmap_file, o_rdwr | o_creat | o_trunc, (mode_t)0600);   result = lseek(hbcast_fd, sizeof(pthread_barrier_t)-1, seek_set);   result = write(hbcast_fd, "", 1);   shared_mem_barrier = (pthread_barrier_t*) mmap(0, sizeof(pthread_barrier_t), prot_read | prot_write, map_shared, hbcast_fd, 0);   if (mpi_rank == 0) {     int err = pthread_barrier_init(shared_mem_barrier, &barattr, host_size);   }   mpi_barrier(some_communicator); } 

questions:

• do miss in mmap initialization?
• which operation should performed processes, , should one?

new question

which safier managing pthread barrier? or based on same mechanism?

• shmget
• shm_open
• mmap
• another one

as charles has mentioned, looks truncation what's getting you. also, should initialise attributes using pthread_barrierattr_init.

as other question, 1 process should initialisation, , processes should call pthread_barrier_wait (just mpi).

i saw other question, know why don't want use mpi. you'd single mpi barrier initialise pthread barriers, so:

if (rank == 0) {   /* create shared memory segment, initialise barrier. */ } mpi_barrier(communicator); if (rank != 0) {   /* load shared memory segment, cast pthread_barrier_t* , store.    * it's initialised */ }