Introduction to C - Threads, Summaries of Programming Languages

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Introduction to C

Threads

Instructor: Yin Lou

Processes vs. Threads

Processes

I Multiple simultaneous

programs

I Independent memory space

I Independent open

file-descriptors

Threads

I Multiple simultaneous

functions

I Shared memory space

I Shared open file-descriptors

Threads

I One copy of the heap

I One copy of the code

I Multiple stacks

Threads

I One copy of the heap

I One copy of the code

I Multiple stacks

I Life Cycle

pthread

I #include <pthread.h>

I Define a worker function

pthread

I #include <pthread.h>

I Define a worker function

I void *foo(void *args) { }

pthread

I #include <pthread.h>

I Define a worker function

I void *foo(void *args) { }

I Initialize pthread attr t

I pthread attr t attr;

I pthread attr init(attr);

pthread

I #include <pthread.h>

I Define a worker function

I void *foo(void *args) { }

I Initialize pthread attr t

I pthread attr t attr;

I pthread attr init(attr);

I Create a thread

pthread

I #include <pthread.h>

I Define a worker function

I void *foo(void *args) { }

I Initialize pthread attr t

I pthread attr t attr;

I pthread attr init(attr);

I Create a thread

I pthread t thread;

I pthread create(&thread, &attr, worker function, arg);

I Exit current thread

pthread

I #include <pthread.h>

I Define a worker function

I void *foo(void *args) { }

I Initialize pthread attr t

I pthread attr t attr;

I pthread attr init(attr);

I Create a thread

I pthread t thread;

I pthread create(&thread, &attr, worker function, arg);

I Exit current thread

I pthread exit(status)

Thread Management

I pthread join(threadid, status)

I pthread detach(threadid)

Example

#include <stdio.h> #include <pthread.h> #define NUM_THREADS 5

void *print_hello(void *threadid) { long tid; tid = (long) threadid; printf("Hello World! It’s me, thread #%ld!\n", tid); pthread_exit(NULL); }

int main (int argc, char *argv[]) { pthread_t threads[NUM_THREADS]; int rc; long t; for (t = 0; t < NUM_THREADS; t++) { printf("In main: creating thread %ld\n", t); rc = pthread_create(threads + t, NULL, print_hello, (void ) t); if (rc) { printf("ERROR; return code from pthread_create() is %d\n", rc); exit(-1); } } / wait for all threads to complete */ for (t = 0; t < NUM_THREADS; t++) { pthread_join(threads[t], NULL); } pthread_exit(NULL); }

Compiling

I Use “-pthread”

Makefile

CC:=gcc

OPTIONS:=-O

LIB_PATH:=-pthread

SRC_DIR:=src

DST_DIR:=bin

default:

$(CC) $(OPTIONS) $(LIB_PATH) \

$(SRC_DIR)/*.c -o $(DST_DIR)/test

clean:

cd $(DST_DIR); rm test