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Whenever threads come into play, there are bounded to be shared memory or resources that each thread wants to access. But because of the random nature of execution of each thread, there will be corruption of data when multiple threads try to read and write into the same memory space. One possible way to fix the problem is using locking mechanism like a mutex. POSIX provides a mutex called pthread_mutex_t just for this purpose. See POS00-C Avoid race conditions with multiple threads
Deadlock can happen when multiple threads each holds a lock the other needs and are waiting for each other to release the resource. One way to fix the problem is to avoid circular wait by locking the mutex in a predefined order.
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