Problem 2. In addition to POSIX semaphores, the POSIX threads standard provides another useful synchronization primitives: the muter (type pthread_mutex_t) A mutex is used to wait for it implement mutual exclusion. A thread locks a mutex variable by calling pthread_mutex_lock(), and unlocks it by calling pthread_mutex_unlock(). When a thread calls pthread_mutex_lock() while another thread has previously locked the same mutex but not yet unlocked it, the former thread blocks until the latter thread calls pthread_mutex_unlock() on it. a. Is there any difference between a binary semaphore and a pthread_mutex? Justify your answer. b. Consider a program with multiple threads running this function: struct {...} shared_data; pthread_mutex_t m; void *thread_func(void *arg) { [update shared_data]; // critical section! return NULL; } Assume the mutex is initialized before the threads are created. Add the necessary pthread_mutex_* calls to the above code to ensure that only one thread is in the critical section at any time. c. Consider the program below, where ". . ." represents code that updates a shared data structure.

Problem 2. In addition to POSIX semaphores, the POSIX threads standard provides another useful synchronization primitives: the muter (type pthread_mutex_t) A mutex is used to wait for it implement mutual exclusion. A thread locks a mutex variable by calling pthread_mutex_lock(), and unlocks it by calling pthread_mutex_unlock(). When a thread calls pthread_mutex_lock() while another thread has previously locked the same mutex but not yet unlocked it, the former thread blocks until the latter thread calls pthread_mutex_unlock() on it. a. Is there any difference between a binary semaphore and a pthread_mutex? Justify your answer. b. Consider a program with multiple threads running this function: struct {...} shared_data; pthread_mutex_t m; void thread_func(void arg) { [update shared_data]; // critical section! return NULL; } Assume the mutex is initialized before the threads are created. Add the necessary pthread_mutex_* calls to the above code to ensure that only one thread is in the critical section at any time. c. Consider the program below, where ". . ." represents code that updates a shared data structure.

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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Question

Problem 2. In addition to POSIX semaphores, the POSIX threads standard provides another
useful synchronization primitives: the muter (type pthread_mutex_t) A mutex is used to wait for
it implement mutual exclusion. A thread locks a mutex variable by calling pthread_mutex_lock(),
and unlocks it by calling pthread_mutex_unlock(). When a thread calls pthread_mutex_lock()
while another thread has previously locked the same mutex but not yet unlocked it, the former
thread blocks until the latter thread calls pthread_mutex_unlock() on it.
a. Is there any difference between a binary semaphore and a pthread_mutex? Justify your answer.
b. Consider a program with multiple threads running this function:
struct {...} shared_data;
pthread_mutex_t m;
void *thread_func(void *arg) {
[update shared_data]; // critical section!
return NULL;
}
Assume the mutex is initialized before the threads are created. Add the necessary pthread_mutex_*
calls to the above code to ensure that only one thread is in the critical section at any time.
c. Consider the program below, where "..." represents code that updates a shared data structure.

void *thread_func (void *arg) {
pthread_mutex_t mymutex;
int rv = pthread_mutex_init(&mymutex,NULL); // default attributes
}
rv = pthread_mutex_lock (&mymutex);
assert (!rv);
... // critical section
rv = pthread_mutex_unlock (&mymutex);
assert (!rv);
return NULL;
The main program creates and executes 4 threads running thread_func(). What is wrong
with the above code? (Hint: it has nothing to do with the variable rv or the call to assert.)

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