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Add initial scheletons

nextime 6 years ago
2 changed files with 221 additions and 0 deletions
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  2. +68

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dotprod_mutex.c View File

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* FILE: dotprod_mutex.c
* This example program illustrates the use of mutex variables
* in a threads program. This version was obtained by modifying the
* serial version of the program (dotprod_serial.c) which performs a
* dot product. The main data is made available to all threads through
* a globally accessible structure. Each thread works on a different
* part of the data. The main thread waits for all the threads to complete
* their computations, and then it prints the resulting sum.
* SOURCE: Vijay Sonnad, IBM
* LAST REVISED: 01/29/09 Blaise Barney
* gcc -Wall -lpthread dotprod_mutex.c -o dotprod_mutex
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>

The following structure contains the necessary information
to allow the function "dotprod" to access its input data and
place its output into the structure. This structure is
unchanged from the sequential version.

typedef struct
double *a;
double *b;
double sum;
int veclen;

/* Define globally accessible variables and a mutex */

#define NUMTHRDS 2
#define VECLEN 100000
DOTDATA dotstr;
pthread_t callThd[NUMTHRDS];
pthread_mutex_t mutexsum;

The function dotprod is activated when the thread is created.
As before, all input to this routine is obtained from a structure
of type DOTDATA and all output from this function is written into
this structure. The benefit of this approach is apparent for the
multi-threaded program: when a thread is created we pass a single
argument to the activated function - typically this argument
is a thread number. All the other information required by the
function is accessed from the globally accessible structure.

void *dotprod(void *arg)

/* Define and use local variables for convenience */

int i, start, end, len ;
long offset;
double mysum, *x, *y;
offset = (long)arg;
len = dotstr.veclen;
start = offset*len;
end = start + len;
x = dotstr.a;
y = dotstr.b;

Perform the dot product and assign result
to the appropriate variable in the structure.
mysum = 0;
for (i=start; i<end ; i++)
mysum += (x[i] * y[i]);

Lock a mutex prior to updating the value in the shared
structure, and unlock it upon updating.
pthread_mutex_lock (&mutexsum);
dotstr.sum += mysum;
printf("Thread %ld did %d to %d: mysum=%f global sum=%f\n",offset,start,end,mysum,dotstr.sum);
pthread_mutex_unlock (&mutexsum);

pthread_exit((void*) 0);

The main program creates threads which do all the work and then
print out result upon completion. Before creating the threads,
The input data is created. Since all threads update a shared structure, we
need a mutex for mutual exclusion. The main thread needs to wait for
all threads to complete, it waits for each one of the threads. We specify
a thread attribute value that allow the main thread to join with the
threads it creates. Note also that we free up handles when they are
no longer needed.

int main (int argc, char *argv[])
long i;
double *a, *b;
void *status;
pthread_attr_t attr;

/* Assign storage and initialize values */

a = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));
b = (double*) malloc (NUMTHRDS*VECLEN*sizeof(double));
for (i=0; i<VECLEN*NUMTHRDS; i++) {

dotstr.veclen = VECLEN;
dotstr.a = a;
dotstr.b = b;

pthread_mutex_init(&mutexsum, NULL);
/* Create threads to perform the dotproduct */
pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE);

/* Each thread works on a different set of data.
* The offset is specified by 'i'. The size of
* the data for each thread is indicated by VECLEN.
pthread_create(&callThd[i], &attr, dotprod, (void *)i);

/* Wait on the other threads */

for(i=0;i<NUMTHRDS;i++) {
pthread_join(callThd[i], &status);
/* After joining, print out the results and cleanup */

printf ("Sum = %f \n", dotstr.sum);
free (a);
free (b);

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pinthread.c View File

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* compile with :
* $ gcc -Wall -D_GNU_SOURCE -fpic -shared -o pinthread.c -ldl -lpthread
* and test it with :
* LD_PRELOAD=/path/to/ something

//#include <sys/types.h>
//#include <unistd.h>
#include <stdio.h>
#include <pthread.h>
#include <dlfcn.h>
#include <sched.h> //cpu_set_t , CPU_SET

typedef struct {
void *arg;
void *(*fn)(void *);
} real_args;

void *create_head(void *arg)
real_args *a = arg;

//fprintf(stderr,"PID %d TID %d\n",
// getpid(),(int)pthread_self());
return a->fn(a->arg);

static int (*real_pthread_create)(pthread_t *thread,
const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);

int pthread_create(pthread_t *thread,
const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg)
//real_args targs;
char *msg;
int ret;
cpu_set_t mask; /* Define your cpu_set bit mask. */
CPU_ZERO(&mask); /* Initialize it all to 0, i.e. no CPUs selected. */
CPU_SET(0, &mask); /* set the bit that represents core 0. */

//targs.arg = arg;
//targs.fn = start_routine;

if (real_pthread_create == NULL)
real_pthread_create = dlsym(RTLD_NEXT,"pthread_create");
if ((msg=dlerror())!=NULL)
printf("**fopen dlopen failed : %s\n", msg);
printf("*wrapping done\n");

printf("*about to call original pthread_create\n");
//return real_pthread_create(thread,attr,create_head,&targs);
ret = real_pthread_create(thread,attr,start_routine,arg);
pthread_setaffinity_np(*thread, sizeof(mask), &mask);
return ret;