/* enqdeq.h */

/* Data structures for condition variable based solution to the */
/* readers and writers problem...                               */

#include <pthread.h>

#define READ  1
#define WRITE 2

/* These Queue Elements are used to represent threads that are    */
/* waiting upon the resource.. They should be dynamically created */
/* using malloc() ONLY IF a thread must wait and should be        */
/* released using free() AT THE TIME the request is granted.      */

struct qeltype
{
   int            tid;      /* For debugging                       */
   int            action;   /* Read or write                       */
   struct qeltype *qnext;   /* Next element in list (or NULL)      */
};

/* This Queue Control block is used to serialize access of a number */
/* of reading or writing threads to a serially reusable resource    */
/* It should reside in the calling program and be properly          */
/* initialized by the calling program.                              */

struct qcbtype
{
   int state;               /* 1 => Read and 2 => write and 0 free */
   int numusing;            /* Number of threads using the resource */
   int numwaiting;          /* Number of waiting threads            */
   pthread_mutex_t mtx;     /* Mutex                                */
   pthread_cond_t  cv;      /* Condition var.                       */
   struct qeltype *qhead;   /* Head of wait queue                   */
   struct qeltype *qtail;   /* Tail of wait queue.                  */
};

/* Function prototypes */

int enqueue(
struct qcbtype *q,          /* Pointer to QCB  */
int            action,      /* READ or WRITE   */
int            tid);        /* Thread id       */

/* Function prototypes */

int dequeue(
struct qcbtype *q,          /* Pointer to QCB */
int            tid);        /* Thread id      */