CODEWITHSUNDEEP
clinuxshared-librariesmutexld-preload
MicrosoctCprog
MicrosoctCprog

Reputation: 490

How to use mutex in shared library that called from multy threads?

I build a share library that used for LD_PRELOAD , that library is called by multy-threads in parallel.

I in the first time that read function call to call for _init function . I don't want to use __attribute__(constructor) because that library load lot of time.

#include <stdio.h>
#include <string.h>
#include <pthread.h>

pthread_mutex_t lock;
static int is_init = 0;
pthread_mutex_t lock;
static void __init()
{
    is_init = 1;
    pthread_mutex_lock(&lock);
    ////////////////////////////////////////////
    if(is_init == 0)
        return;
    print("init.....\n");
    ////////////////////////////////////////////
    pthread_mutex_unlock(&lock);
}

ssize_t read(int fd, void *data, size_t size) {
  if(is_init == 0)
      __init();
  strcpy(data, "I love cats");
  return 12;
}

But how can I init the lock with pthread_mutex_init that will called only 1 time ?

Upvotes: 0

Views: 634

Answers (1)

Erdal K&#252;&#231;&#252;k
Erdal K&#252;&#231;&#252;k

Reputation: 5830

Either

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

or in the __init function

pthread_mutex_init(...);

As kaylum said earlier: "the constructor is only called once per process."

Upvotes: 2

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