Notes

Thread Termination
1) Implicit Termination -> When thread routine returns
2) Explicit Termination -> pthread_exit() function
a) When main thread calls pthread_exit() it waits for all other peer threads to terminate, and then terminates the main thread and the entire process with return value of thread_return
3) Some peer thread calls UNIX exit() function which terminates whole process and all the threads associated with that process.
4) Another peer thread terminates the current thread by calling the pthread_cancel() with the ID of the current thread.

Reaping Terminated Threads
1) Threads wait for other peer thread to terminate by calling the pthread_join() function
#include <pthread.h>
int pthread_join(pthread_t tid, void** thread_return) {} Returns 0 if OK, non-zero if error
pthread_join() blocks untill thread with ID tid terminates, assigns the generic void * pointer returned by the thread routine of thread with ID tid to the location pointed by thread_return and then reaps the memory resources(stacks not heap, because heap is shared by all peer threads) held by current threads
2) Difference between UNIX wait() and pthread_join()
-> wait() can be used to wait on any arbitrary child process but no similar pthread_wait() function exists.
-> pthread_join() can only be used to wait on a particular thread

Shared variables in threaded program:
1) Multiple threads can share the same program variables
Each thread has its own separate thread context which includes a thread ID, stack, stack pointer, Register, Program counter, condition codes.
Each thread shares rest of the process context with the other threads. This includes entire user virtual address space, which consists of read-only text(code), read-write data, the heap, library code and data areas.
2) In an operational sense, it is impossible for one thread to read or write the register values of another thread. On the other hand, any thread can access any location in the shared memory. If some thread modifies a memory location then every other thread will eventually see the change if it reads that location.