1. Threads in C
Caryl Rahn

2. What is a thread? Also known as lightweight processes
A single sequence stream within a process
Threads are not independent of one another like processes
A thread shares with other threads:
code section
Data section
OS resources (open files and signals)
A thread does have its own:
program counter (PC)
Register set
Stack space

3. Why use Multithreading
Way to improve an application through parallelism
For example, a browser has multiple tabs
Threads are faster than processes because
Thread creation is faster
Context switching between threads is much faster
Threads can be terminated easily
Communication between threads is faster

4. C and Multithreading
Multithreading is not supported by the language standard
POSIX threads (Pthreads) are implemented in the gcc compiler
You must include pthread.h
You must link the program with the pthreads library
Include the –lpthread option on the compile line

5. Sample pthread_create has 4 arguments
#include <stdio.h> #include <stdlib.h> #include <pthread.h> // A normal C function that is executed as a thread when its name // is specified in pthread_create() void *myThreadFun(void *vargp) { sleep(1); printf("In Thread \n"); return NULL; } int main() pthread_t tid; printf("Before Thread\n"); pthread_create(&tid, NULL, myThreadFun, NULL); pthread_join(tid, NULL); printf("After Thread\n"); exit(0);
pthread_create has 4 arguments
The first is a pointer to the thread_id set by this function.
The third is NULL
The third is the name of the function to be executed for the thread to be created.
The fourth is used to pass arguments to the thread
Variable thread_id is of type pthread_t is an integer used to identify the thread in the system
After declaring thread_id pthread_create() function is called to create a thread.
pthread_join() is like a wait() for processes. It blocks the calling process until the thread with an identier equal to the first argument terminates