// The thread of the periodic task is running in an infinite loop. I have included a flag and sleep(), so that it executes only for a certain time and then goes to sleep. But, after the modification, I am not getting the output "executing thread" at all. Please suggest, how to modify the use of the sleep function so that I get the output "executing thread" for the time and then it goes to sleep.//
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <time.h>
#include <unistd.h>
int exitflag=0;
struct task_spec_struct
{
char task_type;
int period,r_min,r_max;
}s1;
int gen_rand(int a, int b)
{
srand(time(NULL));
int x = a+(rand()%(b-a));
return x;
}
//task body to utilize CPU to perform computations
void* periodic_task(void* arg)
{
struct task_spec_struct *arg_struct = (struct task_spec_struct*) arg;
int rand_num = gen_rand(arg_struct->r_min, arg_struct->r_max);
while(1)
{
int i, j=0;
for(i=0; i<rand_num; i++)
{
j=j+i;
}
if (exitflag==1)
{
pthread_exit(0);
}
usleep((arg_struct->period)*1000);
printf("Executing thread1");
}
//pthread_exit(0);
}
int main(int argc, char **argv)
{
int num_args = argc-1;
// Creating pthread for periodic task ( runs Thread function to run periodically)
// printf("\nGive task with specifications:");
s1.task_type= 'P';
s1.period= 300;
s1.r_min= 400;
s1.r_max= 500;
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_create(&tid, &attr, periodic_task, &s1);
int ret=sleep(3);
if (ret==0)
{
exitflag=1;
}
pthread_join(&tid, NULL);
}
printf does not flush by default unless you end the string with a newline character. See Why does printf not flush after the call unless a newline is in the format string?.
You are not seeing the output because the buffer is not being flushed. Either add a new line character, or call fflush on stdout.
Related
This is my current code for the Producer-Consumer problem. I compiled it and ran it but nothing is printed. The command line takes in 3 arguments: Sleep time, producer threads, consumer threads. I've tried setting the values as 5, 1, 1 respectively, the sleep timer works but I'm unsure about the rest.
Code for buffer.h:
typedef int buffer_item;
#define BUFFER_SIZE 5
Code for buffer.c:
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include "buffer.h"
buffer_item buffer[BUFFER_SIZE];
void *producer(void *param);
void *consumer(void *param);
pthread_mutex_t mutex;
sem_t empty;
sem_t full;
int insert_item(buffer_item item)
{
do
{
wait(empty);
wait(mutex);
signal(mutex);
signal(full);
}while(1);
return 0;
}
int remove_item(buffer_item *item)
{
do
{
wait(full);
wait(mutex);
signal(mutex);
signal(empty);
}while(1);
return 0;
}
int main(int argc, char *argv[])
{
int sleepTime;
int producerThreads;
int consumerThreads;
int counter_1;
int counter_2;
if(argc != 4)
{
return -1;
}
sleepTime = atoi(argv[1]);
producerThreads = atoi(argv[2]);
consumerThreads = atoi(argv[3]);
srand((unsigned)time(NULL));
for(counter_1 = 0; counter_1 < producerThreads; counter_1++)
{
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_create(&tid, &attr, producer, NULL);
}
for(counter_2 = 0; counter_2 < consumerThreads; counter_2++)
{
pthread_t tid;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_create(&tid, &attr, consumer, NULL);
}
sleep(sleepTime);
return 0;
}
void *producer(void *param)
{
buffer_item item;
int randomTime;
int counter_1 = 0;
while(1)
{
randomTime = rand() % 1000 + 1;
sleep(randomTime);
item = rand();
if(insert_item(item))
{
fprintf(stderr, "Error.");
}
else
{
printf("Producer ID: %lu, Produced Item: %d\n", pthread_self(), item);
printf("The buffer now contains %d items\n", counter_1);
++counter_1;
}
}
}
void *consumer(void *param)
{
buffer_item item;
int randomTime;
int counter_2 = 0;
while(1)
{
randomTime = rand() % 1000 + 1;
sleep(randomTime);
if(insert_item(item))
{
fprintf(stderr, "Error.");
}
else
{
printf("Consumer ID: %lu, Consumed Item: %d\n", pthread_self(), item);
printf("The buffer now contains %d items\n", counter_2);
++counter_2;
}
}
}
So far I've tried declaring the tid separately, skipping sleep and join the threads, but it still doesn't print.
Your code can't possibly run, indeed it doesn't even compile.
Here's a list of issues that need to be addressed:
wait should be sem_wait
signal should be sem_post for semaphores
int sem_wait(sem_t *sem); and int sem_post(sem_t *sem); take the pointer to a semaphore
sem_wait(mutex) and sem_post(mutex) give something like "incompatible type for argument 1 of sem_wait", I guess you want to acquire and release the lock on the mutex like pthread_mutex_lock(&mutex) and pthread_mutex_unlock(&mutex)
in the consumer if(insert_item(item)): item is used uninitialized
still in the consumer you use insert_item instead of remove_item
Coming to the main question "I compiled it and ran it but nothing is printed", it doesn't print anything because producer and consumer call, respectively, insert_item and remove_item and are trapped inside infinite loops (e.g. while(1))
I am trying to make a "guess the number" minigame to get used to pthreads and synchronization. A thread sleeps for 10 seconds, while the other reads input and says whether the number is too big or too low. When the first thread "wakes up", the second thread should no longer read input, regardless if it were executing scanf. When the second thread has read the correct number, the first thread should no longer sleep and ignore the rest of its code.
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <unistd.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
unsigned short quit = 0;
unsigned short won = 0;
void * engine(void * arg);
void * arbiter();
int main(int argc, char** argv) {
int n = rand() % 100;
pthread_t t1, t2;
pthread_create(&t1, NULL, arbiter, NULL);
pthread_create(&t2, NULL, engine, &n);
pthread_join(t1, NULL);
pthread_join(t2, NULL);
return (EXIT_SUCCESS);
}
void * arbiter(){
sleep(10);
quit = 1;
printf("Stop!\n");
}
void * engine(void * arg){
int n = *(int*)arg;
printf("%d\n", n);
while(!quit){
printf("N = ");
int a;
scanf("%d", &a);
if(a < n){
printf("Go higher!\n");
} else if(a > n){
printf("Go lower!\n");
} else{
printf("Bingo!\n");
won = 1;
}
}
}
I don't know how to use mutexes or cond var here, to make the threads work together. Now, when the first thread wakes up, the second will execute the last scanf. How should I implement this correctly and safe?
Hey so I'm trying to create a multithreaded program. The first thread takes in input from std in and stores it in a minheap. The second thread... well for now, all it does is print "sequencer thread works" and nothing else because it doesn't run properly.
Both threads are detached, so they should run simultaneously, and yet for some reason the second thread doesn't run until the first exits. Is it something simple I am overlooking? I'm new to multithreading.
Thanks
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <sys/time.h>
#include "MinHeap.h"
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
void* readerthread(MinHeap minheap, char eventlist[], char timestamp[])
{
char buffer[100];
char input;
int ret, len, fd;
while(1)
{
char *choice;
choice = malloc(50*sizeof(char));
fgets(choice, 50, stdin);
printf("choice = : %s", choice);
if(checkTimestamp(choice)==0)
{
pthread_mutex_lock(&mutex);
addElement(&minheap, choice);
pthread_mutex_unlock(&mutex);
}
free(choice);
printf( "min of minheap: %s\n", getMin(&minheap));
}
void* sequencerthread()
{
printf("sequencer works\n");
fflush(stdout);
pthread_exit(0);
}
int main(int argc, char *argv[])
{
if (argv < 2)
{
printf("not enough arguments. exiting...\n");
return 1;
}
char timestamp[50];
char event[50];
char eventlist[sizeof(char)+170];
int i;
char nowtimestamp[] = "2400/001/00/00/00";
MinHeap minheap;
initializeMinHeap(&minheap, intCompare, sizeof(char)*50);
strcpy(timestamp, argv[1]);
strcpy(event, argv[2]);
pthread_t ignore1, ignore2;
pthread_attr_t attr;
pthread_attr_init(&attr);
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
pthread_attr_setscope(&attr, PTHREAD_SCOPE_SYSTEM);
pthread_create(&ignore1, &attr, readerthread(minheap, eventlist, nowtimestamp), 0);
pthread_create(&ignore2, &attr, sequencerthread, 0);
pthread_attr_destroy(&attr);
pthread_exit(0);
return (EXIT_SUCCESS);
}
This line is the problem:
pthread_create(&ignore1, &attr, readerthread(minheap, eventlist, nowtimestamp), 0);
You're calling readerthread on the main thread and passing its result to pthread_create. Since readerthread never returns, you never even get to the first call to pthread_create, let alone the second one.
You need to call it like this instead:
pthread_create(&ignore1, &attr, readerthread, &readerthread_args);
where readerthread_args is a struct encapsulating the arguments to pass to readerthread. You'll also need to change readerthread to take a single void * argument, cast it to the type of readerthread_args, and unpack the args.
You should have got a whole bunch of warnings from your compiler. Did you remember to turn them on?
Now this is just a little test, and part of a school assignment. In my code printf is not printing at least to me being able to see it. Is this a result of the thread not functioning? The print line works outside of the thread. Thank you for any help.
I am new to threading in c.
#include<stdio.h>
#include<pthread.h>
#include<string.h>
#include<stdlib.h>
void *threadServer(void *arg)
{
printf("This is the file Name: %s\n", arg);
pthread_exit(0);
}
int main(int argc, char* argv[]){
int i=1;
while(argv[i]!=NULL){
pthread_t thread;
pthread_create(&thread, NULL, threadServer,argv[i]);
i++;
}
In your code, the parent thread of execution that created another thread finishes execution without waiting for its child threads to finish. And threads, unlike processes, once the parent thread terminates, all its child threads of execution terminate as well.
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>
void *threadServer(void *arg)
{
printf("This is the file Name: %s\n", (char*)arg);
pthread_exit(0);
}
int main(int argc, char* argv[]){
int i=1;
while(argv[i]!=NULL){
pthread_t thread;
pthread_create(&thread, NULL, threadServer, argv[i]);
i++;
pthread_join(thread, NULL);
}
}
Doing this will allow the thread created to run, until it finishes execution. The pthread_join will wait for the thread to complete its execution and then move ahead.
EDIT
As people did mention in the comments, it is probably worthless trying to spawn a single thread and joining it immediately, making it no better than a single thread of execution. Hence, for the sake of experimentation, the code can be modified as follows:
#include <stdio.h>
#include <pthread.h>
#include <string.h>
#include <stdlib.h>
void *threadServer(void *arg)
{
printf("This is the file Name: %s\n", (char*)arg);
}
int main(int argc, char* argv[]){
int i = 1;
pthread_t thread[argc - 1];
while(i < argc)
{
pthread_create(&thread[i-1], NULL, threadServer, argv[i]);
i++;
}
for (i = 0; i < argc - 1; ++i)
{
pthread_join(thread[i], NULL);
}
}
I've spent quite a few hours on trying to figure this one out and I'm completly stuck. The program is supposed to start 6 threads. Where some threads start where others end. Right now, I'm trying to get one single thread (thread 0) to execute. The caps lock commenting shows where I have added code and done my mistakes. My main struggle here is dealing with the pointers. Could anyone give me any pointers (ha..ha.. :c )?
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
#define SHARED 1
sem_t sem[6];
struct threadargs
{
int id; /* thread number */
int sec; /* how many sec to sleep */
int signal[6]; /* which threads to signal when done */
};
void *tfunc(void *arg)
{
int i;
struct threadargs *targs=arg;
sem_wait(sem); //WAIT FOR OWN SEMAPHORE
printf("Thread %d is running\n", targs->id);
sleep(targs->sec);
printf("Thread %d is completed and may wake others..\n", targs->id);
for(i=0; i<6; i++) //ITERATE OVER signal_ARRAY &
{ //WAKE THREAD NUMBER i IF
if(targs->signal[i] == 1) //signal[i] IS 1
pthread_cond_signal(&sem[i]);
}
}
int main(void)
{
int i, j;
struct threadargs *targs[6];
pthread_t tid[6];
for(i=0; i<6; i++)
{
targs[i] = (struct threadargs*) malloc(sizeof(struct threadargs));
for(j=0; j<6; j++)
{ targs[i]->signal[j]=0; }
}
targs[0]->id=1;
targs[0]->sec=1;
targs[0]->signal[1]=1;
targs[0]->signal[4]=1;
sem[0] = 0; //INITIALIZE THREAD'S SEMAPHORE TO 0 or 1
pthread_create(targs[0], NULL, tfunc, NULL) // START THREAD
for(i=0; i<6; i++)
pthread_join(tid[i], NULL);
return 0;
}
Alright. First things first, I do recommend taking a second look at your coding style. It is of course highly subjective and I won't say yours is bad, but it took me a while to figure it out (if you really want to know, I recommend the Linux coding style for C/C++ code).
Lets get on with your problem. As far as I can see, the main issue seems that you're basically comparing pointers to apples with pointers to banana's (in other words, you're using the wrong pointer type in the wrong place).
To make sure that calls to functions and the like are correct, make sure to look up the API documentation for functions that are new to you (examples: pthread_create, sem_init, sem_wait, sem_post, pthread_cond_signal).
As you can see, pthread_cond_signal doesn't take a sem_t* as argument, and therefore you can't pass one to it and expect it to work. Below you'll find an example program showing how semaphores are used.
First, a new thread is created which will be put in waiting state instantly. As soon as the main tread finished counting from 0 to 150, it will post ('unlock') the semaphore and allowing the second thread to finish its execution.
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <semaphore.h>
static sem_t sem_thread_one;
static pthread_t thread_one_data;
static int x;
static void *tfunc(void *arg)
{
sem_wait(&sem_thread_one);
printf("Thread 1 is running. The value of x is %i\n", x);
return NULL;
}
int main(int argc, char **argv)
{
sem_init(&sem_thread_one, 0 /* don't share between processes */, 0);
if(pthread_create(&thread_one_data, NULL, &tfunc, NULL)) {
fprintf(stderr, "Could not create thread, exiting!\n");
return -EXIT_FAILURE;
}
while(x < 150) {
x++;
}
sem_post(&sem_thread_one);
if(pthread_join(thread_one_data, NULL)) {
fprintf(stderr, "Could not join threads, exiting!\n");
return -EXIT_FAILURE;
}
sem_destroy(&sem_thread_one);
printf("Program ran succesfully!\n");
return -EXIT_SUCCESS;
}
Save in a file sem.c and compile & link using:
gcc -Wall -Os -pthread -o sem_test sem.c
Now a second example, but now using pthread_cond_t. The functionality of the program is somewhat similar, it waits for a counter to reach a certain number.
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
static pthread_t thread_one_data, thread_two_data;
static volatile int x, y, idx = 10;
static int count = 1;
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t condition = PTHREAD_COND_INITIALIZER;
static void *cond_test_wait(void *arg)
{
pthread_mutex_lock(&mutex);
while(count < 10) {
printf("Waiting for `count < 10' to become true\n");
pthread_cond_wait(&condition, &mutex);
}
pthread_mutex_unlock(&mutex);
printf("Test wait thread finished. Value of count: %i\n", count);
return NULL;
}
static void *cond_test_signal(void *arg)
{
while(count < 10) {
pthread_mutex_lock(&mutex);
pthread_cond_signal(&condition);
/* do more intelligent things here */
count++;
pthread_mutex_unlock(&mutex);
}
printf("Test signal thread finished\n");
return NULL;
}
int main(int argc, char **argv)
{
if(pthread_create(&thread_one_data, NULL, &cond_test_wait, NULL)) {
fprintf(stderr, "Could not create thread, exiting!\n");
return -EXIT_FAILURE;
}
if(pthread_create(&thread_two_data, NULL, &cond_test_signal, NULL)) {
fprintf(stderr, "Could not create thread, exiting!\n");
return -EXIT_FAILURE;
}
pthread_join(thread_one_data, NULL);
pthread_join(thread_two_data, NULL);
pthread_cond_destroy(&condition);
pthread_mutex_destroy(&mutex);
printf("Program ran succesfully!\n");
return -EXIT_SUCCESS;
}
Save in a file cond.c and compile & link using:
gcc -o cond -pthread -Os -Wall cond.c
Do note how neat condition work in this example. You can use them to wait until any expression (= condition) becomes true. After the condition becomes true normal execution continue's.
If you need any more help, don't hesitate to ask in the comments. Good luck combining the above examples to fix up your program.