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- File : rw.c
- Title : Demo Readers/Writer.
- Short : A solution to the multi-reader's, one writer problem.
- Long :
- Author : Andrae Muys
- Date : 18 September 1997
- Revised : */
#include <pthread.h> #include <stdio.h> #include <unistd.h> #include <stdlib.h>
#define MAXCOUNT 5
#define READER1 50000 #define READER2 100000 #define READER3 400000 #define READER4 800000 #define WRITER1 150000
typedef struct { pthread_mutex_t *mut; int writers; int readers; int waiting; pthread_cond_t *writeOK, *readOK; } rwl;
rwl *initlock (void); void readlock (rwl *lock, int d); void writelock (rwl *lock, int d); void readunlock (rwl *lock); void writeunlock (rwl *lock); void deletelock (rwl *lock);
typedef struct { rwl *lock; int id; long delay; } rwargs;
rwargs *newRWargs (rwl *l, int i, long d); void *reader (void *args); void *writer (void *args);
static int data = 1;
int main () { pthread_t r1, r2, r3, r4, w1; rwargs *a1, *a2, *a3, *a4, *a5; rwl *lock;
lock = initlock (); a1 = newRWargs (lock, 1, WRITER1); pthread_create (&w1, NULL, writer, a1); a2 = newRWargs (lock, 1, READER1); pthread_create (&r1, NULL, reader, a2); a3 = newRWargs (lock, 2, READER2);
pthread_create (&r2, NULL, reader, a3); a4 = newRWargs (lock, 3, READER3); pthread_create (&r3, NULL, reader, a4); a5 = newRWargs (lock, 4, READER4); pthread_create (&r4, NULL, reader, a5); pthread_join (w1, NULL); pthread_join (r1, NULL); pthread_join (r2, NULL); pthread_join (r3, NULL); pthread_join (r4, NULL); free (a1); free (a2); free (a3); free (a4); free (a5);
return 0; }
rwargs *newRWargs (rwl *l, int i, long d) { rwargs *args;
args = (rwargs *)malloc (sizeof (rwargs)); if (args == NULL) return (NULL); args->lock = l; args->id = i; args->delay = d; return (args); }
void *reader (void *args) { rwargs *a; int d;
a = (rwargs *)args;
do { readlock (a->lock, a->id); d = data; usleep (a->delay); readunlock (a->lock); printf ("Reader %d : Data = %d\n", a->id, d); usleep (a->delay); } while (d != 0); printf ("Reader %d: Finished.\n", a->id);
return (NULL); }
void *writer (void *args) { rwargs *a; int i;
a = (rwargs *)args;
for (i = 2; i < MAXCOUNT; i++) { writelock (a->lock, a->id); data = i; usleep (a->delay); writeunlock (a->lock); printf ("Writer %d: Wrote %d\n", a->id, i); usleep (a->delay); } printf ("Writer %d: Finishing...\n", a->id); writelock (a->lock, a->id); data = 0; writeunlock (a->lock); printf ("Writer %d: Finished.\n", a->id);
return (NULL); }
void writeunlock (rwl *lock) { pthread_mutex_lock (lock->mut); lock->writers--; pthread_cond_broadcast (lock->readOK); pthread_mutex_unlock (lock->mut); }
void deletelock (rwl *lock) { pthread_mutex_destroy (lock->mut); pthread_cond_destroy (lock->readOK); pthread_cond_destroy (lock->writeOK); free (lock);
return; }
