Semaphore used to synchronize threads of local process &limitations

/MY PROGRAM ARE COMPILED IN FEDORA15 ..WITH 4.6 gcc compiler...../

 /*A semaphore is used to synchronise the threads*/

 2 //In this function semaphore may be acquired by any of thread at any time...so no sy    nchronisation will be maintains in executing the threads ...

  3 //so global data may be changed by any of thread at any instant of time

  4 //suppose there r four fun open..read ..write..close..close may be executed 1st befo    re read

  5 //if i applied semaphore before pthread_create...work of pthread_create is only to c    reate a thread ..not to wait finishing of function started when this thread created.    .so in mid of execution of that func..it will release the semaphore & give it to ano    ther pthread_create

  6 //when main ends ....every thread will be finished..

  7 //but benefit of semaphore will be seen when i will use it globaly..means for more t    han one process....it will sychronise threads b/w two distinct process...

  8 //suppose i have open write read close function in two applications & both applicati    ons will execute at same time as foreground process as used & b/w files...then it wi    ll do write of 1st app ...then write of another app..

  9 //i want 1st open write read & close occur in 1st app...then open write read & close     in  another app...so could be synchronised by using global semaphore of threads

 10 #include<stdio.h>

12 #include<stdlib.h>

 13 #include<string.h>

 14 #include<pthread.h>

 15 #include<semaphore.h>

 16 void* thread_fun1(void*);

 17 void* thread_fun2(void*);

 18 void* thread_fun3(void*);

 19 void* thread_fun4(void*);

 20 char buff[24],set[20];//used two global variables...shared by all threads

 21 sem_t mutex;//variable of semaphore is declared

 22 int main()

 23     {

 24         int lv;

 25         void* retval;

 26         char *message="THIS IS LINUX";

 27         pthread_t tid1,tid2,tid3,tid4;

28         if(!sem_init(&mutex,0,1))//semid will in mutex..2nd arg is value of pshared.    ...i.e.if pshared=0 means this semaphore may be used local to this  process ...if ps    hared=1...means this same semaphore may be used extern to this process

 29             printf("sem_init is initialised\n");

 30         printf("mutex=%p\n",&mutex);

 31       //sem_wait(&mutex);

 32         lv=pthread_create(&tid1,NULL,thread_fun1,(void*)message);

 33       if(lv==0)

 34       {

 35           printf("thread 1 is created\n");

 36       }

 37     //sem_post(&mutex);

 38       //pthread_join(tid1,&retval);

 39       //printf("retval=%s\n",(char*)retval);

 40

 41       message="THIS IS WINDOWS";

 42       //sem_wait(&mutex);

43         lv=pthread_create(&tid2,NULL,thread_fun2,(void*)message);

 44       if(lv==0)

 45       {

 46           printf("thread 2 is created\n");

 47       }

 48     //sem_post(&mutex);

 49       //pthread_join(tid2,&retval);

 50       //printf("retval=%s\n",(char*)retval);

 51       message="THIS IS 8051";

 52