CS 3733 Operating Systems Notes: Threads

Introduction

We have studied using multiple processes using fork.

If these processes need to communicate, an external mechanism (such as signals or pipes) must be used.

A thread is a a flow of control in a process.

Multiple threads share the same address space.

If one thread changes a variable, this change can be seen by other threads.

You create a thread by indicating the name of a function for the thread to execute.
Unlike an ordinary call, the created and creating threads execute concurrently.

A thread of execution for an ordinary call to process_fd.

A new thread executes process_fd.

Motivating Problem: Monitoring file descriptors:

• Create a separate process to monitor each file descriptor.
• Use nonblocking I/O with polling.
• Use asynchronous I/O with the SIGPOLL signal.
• Use POSIX asynchronous I/O
• Use select to block until input is available.
• Use poll to block until input is available.
• Create a separate thread to monitor each file descriptor.

  #include <pthread.h>
 
  int pthread_create(pthread_t *tid, const pthread_attr_t *attr,
                 void *(*start_routine)(void *), void *arg);
  void pthread_exit(void *value_ptr);
  int pthread_join(pthread_t thread, void **value_ptr);

• tid points to the place to put the thread ID
• the second parameter is a set of attributes for the thread.
  NULL means use the defaults
• the third parameter is the function to execute
  it takes one pointer parameter and returns a pointer of arbitrary type
• the last parameter to pthread_create is the argument passed to the above function

pthread_exit: allows a return value to be passed to another thread that joins to it.

pthread_join: wait for the thread with a given thread ID.

Look at Program 9.4: using select

Look at Program 9.6: a function that monitors a file descriptor

Look at Example 9.3: a code segment that calls process_fd as an ordinary function

Look at Example 9.4: a code segment that creates a thread ro run process_fd

Look at Program 9.7: a function to monitor an array of file descriptor using threads.

POSIX Threads

Description	POSIX function
Thread Management	pthread_create
	pthread_exit
	pthread_kill
	pthread_join
	pthread_self
Mutual Exclusion	pthread_mutex_init
	pthread_mutex_destroy
	pthread_mutex_lock
	pthread_mutex_trylock
	pthread_mutex_unlock
Condition Variables	pthread_cond_init
	pthread_cond_destroy
	pthread_cond_wait
	pthread_cond_timedwait
	pthread_cond_signal
	pthread_cond_broadcast