Re: mutex example

"Chris Thomasson" <>
Tue, 22 Jul 2008 08:42:48 -0700
<> wrote in message

can any one give a simple example for implementing mutex.

Sure... Here is some pseudo-code:
class mutex {
  enum constant {
    UNLOCKED = 0,
    LOCKED = 1,

  atomic_word m_state;
  event m_waitset;

  mutex() : m_state(UNLOCKED) {}

  void lock() {
    if (ATOMIC_SWAP(&m_state, LOCKED)) {
      while (ATOMIC_SWAP(&m_state, CONTENTION)) {
    MEMBAR #StoreLoad | #StoreStore;

  void unlock() {
    MEMBAR #LoadStore | #StoreStore;
    if (ATOMIC_SWAP(&m_state, UNLOCKED) == CONTENTION) {

I have 3 threads (taking different input files )enter into the same
function at different times...

The 3 threads need to exit/leave the function till all the input files
reached till end which are taken as input to the threds.

Do you need mutual exclusion amongst the three threads or not? If you do,
then only a single thread will ever be executing code within the
critical-section at any one time. If not, then you could use a barrier
synchronization object at the end of the function. Basically, something like
Pascal suggested. Except, POSIX has a barrier already, you don't need to
implement one from mutexs and conditions. Something like; modulo any typos
with error checking omitted:

class barrier {
  pthread_barrier_t m_waitset;

  barrier(unsigned count) {
    pthread_barrier_init(&m_waitset, NULL, count);

  ~barrier() {

  void wait() {

You can use it like:
static barrier* g_barrier = NULL;

int main() {
  barrier m_barrier(3);
  g_barrier = &m_barrier;
  return 0;

void Your_Function_For_The_Three_Threads(...) {


thanks to all

No problem.

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