I have to use the clone() system call in the main-function to get 2 threads. (I know, there are other options, but in this case, it has to be clone()).
The system call works and both threads arrive in the designated function (foo). But in this function I need them to call another function with this signature:
void increment(int* a, int b)
(Sidenote: It adds b * 1 to a. (= a+b))
The important thing is, that both, a and b, are declared in the main-function and I don't know how to pass them to foo.
I already tried different things, but without success. I've gotten a hint: Use an adapter.
But I have no clue how to do this. (I also dont know how to use the args in clone with int.)
Any suggestions?
One of the arguments to clone() is a void* arg. This lets you pass a void pointer to your function. In order to pass an int pointer and an int instead, you have to create a struct with an int pointer and int assigned to a and b respectively, then cast a pointer to that struct into a void pointer. Then inside the function you reverse the process.
My C is a little rusty and I haven't compiled this, so don't quote me on it, but it should look roughly like this:
struct clone_args {
int* a;
int b
};
int main(int argc, char* argv[])
{
struct clone_args args;
args.a = a;
args.b = b;
void* arg = (void*)&args;
clone(fn, ..., arg, ...);
}
int fn(void* arg)
{
struct clone_args *args = (struct clone_args*)arg;
int* a = args->a;
int b = args->b;
}
Note: take care that the struct you create is still in scope when fn is called, as it isn't copied. You might have to malloc it.
Here is the example code:
#define stacksize 1048576
typedef struct
{
int ii;
int jj;
} someinput1;
static int /* Start function for cloned child */
childFunc(someinput1 *struc)
{
printf("Child: PID=%ld PPID=%ld\n", (long) getpid(), (long) getppid());
printf("Hi!! I am child process created by Clone %ld \n",(long) getpid());
printf("Value of x %d %d\n",struc->ii,struc->jj);
}
int main()
{
someinput1 inputtest;
int i;
char *stack; /* Start of stack buffer */
char *stack1; /* End of stack buffer */
pid_t pid;
stack = malloc(stacksize);
stack1 = stack + stacksize;
for (i = 0;i<5;i++)
{
inputtest.ii = i+5;
inputtest.jj = inputtest.ii + 10;
pid = clone(childFunc, stack1, NULL, (void *) (&inputtest));
printf("clone returned -- %ld \n", (long) pid);
}
sleep(1);
exit(EXIT_SUCCESS);
}
Related
I am having issues trying to send multiple arguments to the pthread_create, the issue is basically because one of the arguments is another struct.
This is the node.
#include <stdio.h>
#include <string.h>
#include <pthread.h>
#include <stdlib.h>
#define NUM_THREADS 4
struct arr {
char line[10];
};
struct args {
struct arr record; int count; int init; int end;
};
void* processarr(void *arguments)
{
int count; int init; int end;
struct args *argstmp=arguments;
init=argstmp->init;
count=argstmp->count;
end=argstmp->end;
struct arr record[count];
record=(struct arr)argstmp->record;
printf("Some of the vals are init %d count %d end %d\n",init, count, end);
printf("vals like record 0\n", record[0].line);
pthread_exit(NULL);
}/*end of processarr*/
int main (int argc, char *argv[])
{
int line_count;
FILE *ptr_file;
char buf[10];
ptr_file =fopen(argv[ 1 ],"r");
if (!ptr_file)
return 1;
while (fgets(buf,10, ptr_file)!=NULL)
{
line_count++ ;
}
rewind(ptr_file);
struct arr record[line_count];
line_count=0;
while (fgets(buf,10, ptr_file)!=NULL)
{
line_count++ ;
buf[strcspn(buf, "\r\n")] = 0; /* Removing end null chars*/
strcpy(record[line_count].line,buf);
}
float grptmp,group, lgroup;
grptmp=line_count/NUM_THREADS;
int counter1,counter2,init,end;
counter2=1;
struct args myargs;
//processarr(record, line_count, init, end);
pthread_t threads[NUM_THREADS];
for (counter1=0;counter1<=line_count;counter1++)
{
if(counter2==NUM_THREADS)
{
end=line_count;
}else{
end=counter1+grptmp;
}
init=counter1;
myargs.record=*record;
myargs.count=line_count;
myargs.init=init;
myargs.end=end;
printf ("Run job #%d with paramts Init=%d and End=%d\n",counter2, init, end);
//call here
//struct arr *record; int count; int init; int end;
int rc;
long t;
for(t=0;t<NUM_THREADS;t++){
rc = pthread_create(&threads[t], NULL,processarr,&myargs);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
counter1=counter1+grptmp;
counter2++;
}
return 0;
}
So, when I send my arguments,the one stored inside myargs.record=*record, for some reason I am not able to "unpack" it once in the function.
The function is was defined as void to be able to catch the whole big argument, and I am trying to re-map everything there, the counts are working fine, but the one called record, that is actually another struct is not working, looks like a cast issue.
void* processarr(void *arguments)
{
int count; int init; int end;
struct args *argstmp=arguments;
init=argstmp->init;
count=argstmp->count;
end=argstmp->end;
struct arr record[count];
record=(struct arr)argstmp->record;
printf("Some of the vals are init %d count %d end %d\n",init, count, end);
printf("vals like record 0\n", record[0].line);
pthread_exit(NULL);
}
I am getting the following error when compiling.
test4.c: In function processarr:
test4.c:31:7: error: assignment to expression with array type
record=(struct arr)argstmp->record;
Any idea why this is not working? This last one was my last change using the casting (struct arr) in front of the argstmp (which is supposed to have everything inside).
Elaborating a little more on my response, this is what I would do using another struct to pass the arguments.
typedef struct {char line[10];}mystruct;
typedef struct {mystruct struct1;char line[10];}wrapper;
struct wrapper2 {mystruct struct1;char line[10];};
void unwrap(struct wrapper2 args){
printf("val is %s\n",args.line);
mystruct tmp=args.struct1;
printf("val inside structure is %s\n\n", tmp.line);
}
int main ()
{
mystruct names;
strcpy(names.line,"TEST");
struct wrapper2 wrapper1;
wrapper1.struct1=names;
strcpy(wrapper1.line,"Value1");
unwrap (wrapper1);
}
I hope this example helps you fix the issue, you just need to pass the same thing using the pthread_create.
Update:
The final code could look like this:
#include <pthread.h>
#include <stdlib.h>
struct mystruct {
int val;
};
void * func (void *args){
struct mystruct *st1=args;
printf("Thread created..%d\n", st1->val);
pthread_exit(NULL);
}
int main ()
{
/* Thread creation logic as void * (*)(void *)
int pthread_create (pthread_t *, const pthread_attr_t *,
void *(*)(void *), void *);
* */
struct mystruct mystruct1;
mystruct1.val=230;
pthread_t threads;
pthread_create(&threads,NULL,&func,&mystruct1);
pthread_exit(NULL);
return 0;
}
I recommend you read the actual manual of pthread_create.
http://man7.org/linux/man-pages/man3/pthread_create.3.html
After some research I didn't find a good way to implement the std::bind in C.
I build a small program that implements an equivalent of std::bind in C by hacking the stack.
There's two functions I will try to bind to function with pre-defined arguments.
My problem is this code is only working under Windows. Under Linux, this is a mess. I this the problem is my knowledge of the stack and the way that arguments are store in memory.
Thanks,
Please, find below the code I made:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
The two functions I want to bind :
void test1 (int nombre, char t, int nombre2)
{
printf ("test 1 : %d%c%d\n", nombre, t, nombre2);
}
void test2 (char t, int nombre, int nombre2)
{
printf ("test 2 : %c%d%d\n", t, nombre, nombre2);
}
Two struct that will store the argument of each function (order of fields is important).
typedef struct {
int nombre;
char t;
int nombre2;
} struct1;
typedef struct {
char t;
int nombre;
int nombre2;
} struct2;
This "fake" struct will be use to write on the stack by dereferencing a structvoid* variable.
// Size must be bigger than every struct*
typedef struct {
int i[10];
} structvoid;
The main function.
int main(int argc, char** argv) {
// Variables to store the two functions and their arguments.
void * functions[2];
structvoid * data[2];
void *func1 = (void *)&test1;
void *func2 = (void *)&test2;
void (*functionPtrc)(structurevoid);
// Definition of the argument of the first function test1
struct1 data1;
data1.nombre = 15;
data1.t = 'c';
data1.nombre2 = 30;
// and storing data.
void *datac = malloc (sizeof (structvoid));
memcpy(datac, &data1, sizeof (struct1));
data[0] = (structvoid*)datac;
functions[0] = func1;
// Same thing with function 2.
struct2 data2;
data2.t = 'a';
data2.nombre = 5;
data2.nombre2 = 10;
datac = malloc (sizeof (structvoid));
memcpy(datac, &data2, sizeof (struct2));
data[1] = (structvoid*)datac;
functions[1] = func2;
// Get the pointer to the first function (test1);
functionPtrc = functions[0];
// All the hack is here. By dereferencing the data, this will write on the stack all arguments need by the test1 function.
functionPtrc(*data[0]);
functionPtrc = functions[1];
functionPtrc(*data[1]);
// To check the result.
test1 (data1.nombre, data1.t, data1.nombre2);
test2 (data2.t, data2.nombre, data2.nombre2);
return 0;
}
EDIT
Here a new version of the program by calling function via the calling convention. I only wrote the new lines. The problem of this method is I can only store data inside a "void *" field. If I increase the size of structvoid, I got garbage behaviors.
// Structure that memories each argument
typedef struct {
void *i[1];
} structvoid;
int main(int argc, char** argv) {
// Variables to store the two functions and their arguments.
void * functions[2];
structvoid * data[2];
void *func1 = (void *)&test1;
// Let's start with a maximum of 5 arguments
void (*functionPtrc)(structurevoid, structurevoid, structurevoid, structurevoid, structurevoid);
// Definition of the argument of the first function test1
struct1 data1;
data1.nombre = 15;
data1.t = 'c';
data1.nombre2 = 30;
// and storing data.
structvoid *datac = malloc (sizeof (structvoid)*5);
memcpy(&datac[0], &data1.nombre, sizeof (data1.nombre));
memcpy(&datac[1], &data1.t, sizeof (data1.t));
memcpy(&datac[2], &data1.nombre2, sizeof (data1.nombre2));
data[0] = datac;
functions[0] = func1;
// Get the pointer to the first function (test1);
functionPtrc = functions[0];
// Call the function with the arguments. The unused argument will be ignored.
functionPtrc(data[0][0], data[0][1], data[0][2], data[0][3], data[0][4]);
}
I'm having a trouble passing a struct pointer into a function because I'm a bit confused with those pointers and references. I want to modify the thread.thread_num value from the thread_startfunction.
#include <stdio.h>
#include <stdlib.h> //malloc, free
#include <pthread.h>
#define N 5
// void *malloc(size_t);
struct thread {
pthread_t thread_id;
int thread_num;
// int thread_sum;
};
void *thread_start(void *thread)
{
struct thread *my_data;
my_data = (struct thread *)thread;
printf("num T: %i\n", my_data->thread_num);
my_data->thread_num=4;
printf("num T: %i\n", my_data->thread_num);
return NULL;
}
int main(int argc, char *argv[])
{
int i;
struct thread pthread_data;
struct thread *thread = &pthread_data;
thread->thread_num=2;
pthread_create(&thread->thread_id, NULL, thread_start, (void *)&thread);
printf("num: %i\n",thread->thread_num);
pthread_exit(NULL);
return 0;
}
But the value that print the main doesn't change (2).
And then I want to create an array of thread struct, but I don't know how exactly do that:
I guess it should be something like this:
int main(int argc, char *argv[])
{
int i;
struct thread pthread_data;
struct thread *thread[N-1] = &pthread_data; // I don't know how to manage this.
for(i=0; i<N; i++)
{
thread->thread_num=i;
pthread_create(&thread[i]->thread_id, NULL, thread_start, (void *)&thread[i]);
printf("num %i: %i\n",i,thread[i]->thread_num);
}
pthread_exit(NULL);
return 0;
}
Any thoughts?
I recommend you to read http://www.advancedlinuxprogramming.com/alp-folder/alp-ch04-threads.pdf
And here what you wanted:
#define N 5
typedef struct thread {
pthread_t thread_id;
int thread_num;
// int thread_sum;
} ThreadData;
void *thread_start(void *thread)
{
ThreadData *my_data = (ThreadData*)thread;
//there is no guarantee that prints will be in order
// we will use its initial thread->num ,cause it differs for each thread
//plus you will see how threads will behave
int order=my_data->thread_num;
printf("%i) before num T: %i\n",order, my_data->thread_num);
my_data->thread_num=4;
printf("%i) after assignment num T: %i\n",order ,my_data->thread_num);
return NULL;
}
int main(int argc, char *argv[])
{
int i;
ThreadData thread[N];
for(i=0; i<N; i++)
{
thread[i].thread_num=i;
pthread_create(&(thread[i].thread_id), NULL, thread_start, (void *)(thread+i));
}
//wait for all threads
for (i = 0; i < N; i++)
pthread_join(thread[i].thread_id, NULL);
//print results of each thread
for (i = 0; i < N; i++)
printf(" %i)thread: number %i\n",i,thread[i].thread_num);
return 0;
}
I can see multiple mistakes in your code.
First you have your pointers wrong. In the first example, it is enough to pass &pthread_data to pthread_create, &thread is the address of the thread pointer, so you are passing struct thread ** to your function instead of struct thread *. In the second example you should use (void *) thread[i]. &thread[i] is again struct thread **.
When you want each thread to write to its own thread data, then you should make an array of thread data, so that each thread has its own piece, else you will run into race conditions.
As others have already pointed out, you should call pthread_join before calling printf to ensure that the main thread will wait for all worker threads.
Also note that if you are calling pthread_join from other function that the one that spawned those threads, you have to ensure that the array of tread data will not go out of scope (in this case it would be probably better to use malloc or a global array).
You can't. As soon as main exits, which it does when you call pthread_exit, pthread_data ceases to exist, since it's local to the main function. So it can't be modified.
If I am going to create a pthread for the following function.
Assume everything is properly delared.
pthread_create(&threadId, &attr, (void * (*)(void*))function, //what should be the arguments for here??);
int a = 0;
int b = 1;
//c and d are global variables.
void function(int a, int b){
c = a;
d = b;
}
This does not work. function() has to take exactly one argument. That's why you have to do this:
(void * ()(void))
You're telling your compiler "no, seriously, this function only takes one argument", which of course it doesn't.
What you have to do instead is pass a single argument (say a pointer to a struct) which gets you the information you need.
Edit: See here for an example: number of arguments for a function in pthread
The pthread thread function always takes one void * argument and returns a void * value. If you want to pass two arguments, you must wrap them in a struct - for example:
struct thread_args {
int a;
int b;
};
void *function(void *);
struct thread_args *args = malloc(sizeof *args);
if (args != NULL)
{
args->a = 0;
args->b = 1;
pthread_create(&threadId, &attr, &function, args);
}
and for the thread function itself:
void *function(void *argp)
{
struct thread_args *args = argp;
int c = args->a;
int d = args->b;
free(args);
/* ... */
You don't need to use malloc() and free(), but you must somehow ensure that the original thread doesn't deallocate or re-use the thread arguments struct until the called thread has finished with it.
I have the following functions :
void *foo(void *i) {
int a = (int) i;
}
int main() {
pthread_t thread;
int i;
pthread_create(&thread, 0, foo, (void *) i);
}
At compilation, there are some errors about casting ((void *) i and int a = (int) i). How can I pass an integer as the last argument of pthread_create properly?
Building on szx's answer (so give him the credit), here's how it would work in your for loop:
void *foo(void *i) {
int a = *((int *) i);
free(i);
}
int main() {
pthread_t thread;
for ( int i = 0; i < 10; ++1 ) {
int *arg = malloc(sizeof(*arg));
if ( arg == NULL ) {
fprintf(stderr, "Couldn't allocate memory for thread arg.\n");
exit(EXIT_FAILURE);
}
*arg = i;
pthread_create(&thread, 0, foo, arg);
}
/* Wait for threads, etc */
return 0;
}
On each iteration of the loop, you're allocating new memory, each with a different address, so the thing that gets passed to pthread_create() on each iteration is different, so none of your threads ends up trying to access the same memory and you don't get any thread safety issues in the way that you would if you just passed the address of i. In this case, you could also set up an array and pass the addresses of the elements.
You can allocate an int on the heap and pass it to pthread_create(). You can then deallocate it in your thread function:
void *foo(void *i) {
int a = *((int *) i);
free(i);
}
int main() {
pthread_t thread;
int *i = malloc(sizeof(*i));
pthread_create(&thread, 0, foo, (void *) i);
}
You should cast the address of i (rather than the value of i as you do now) in the last argument of pthread_create().
pthread_create(&thread, 0, foo, (void *) &i);
^ is missing
And the casting is wrong in your function too. It should be:
int a = *((int*) i);
If you intend to read the value, you should also initialize i to some value in main() as it's uninitialized now.
2 Use proper definition for main():
int main(void)
or int main(int argc, char *argv[]) or its equivalent.
Old question, but I faced the same problem today, and I decided not to follow this path.
My application was really about performance, so I chose to have this array of ints declared statically.
Since I don't know a lot of applications where your pthread_join / pthread_cancel is in another scope than your pthread_create, I chose this way :
#define NB_THREADS 4
void *job(void *_i) {
unsigned int i = *((unsigned int *) _i);
}
int main () {
unsigned int ints[NB_THREADS];
pthread_t threads[NB_THREADS];
for (unsigned int i = 0; i < NB_THREADS; ++i) {
ints[i] = i;
pthread_create(&threads[i], NULL, job, &ints[i]);
}
}
I find it more elegant, more efficient, and you don't have to worry about freeing since it only lives in this scope.
While this is an old question there is one option missing when all you need is to pass a positive integer like a descriptor: you can pass it directly as the address, while it it a hack it works well and avoid allocating anything :)
NOTE: the size of the integer must match the size of a pointer on your OS but nowadays most systems are native 64bits.
#include <pthread.h>
#include <inttypes.h>
#include <stdio.h>
void *_thread_loop(void *p)
{
uint64_t n = (uint64_t)p;
printf("received %llu\n", n);
return NULL;
}
int main(int argc, char const *argv[])
{
pthread_t read_thread_id;
uint64_t n = 42;
pthread_create(&read_thread_id, NULL, _thread_loop, (void *)n);
pthread_join(read_thread_id, NULL);
return 0;
}