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/*

 * This file contains the old semaphore code that we need to

 * preserve for glibc-2.0 backwards compatibility. Port to glibc 2.1

 * done by Cristian Gafton.

 */

/* Linuxthreads - a simple clone()-based implementation of Posix        */

/* threads for Linux.                                                   */

/* Copyright (C) 1996 Xavier Leroy (Xavier.Leroy@inria.fr)              */

/*                                                                      */

/* This program is free software; you can redistribute it and/or        */

/* modify it under the terms of the GNU Library General Public License  */

/* as published by the Free Software Foundation; either version 2       */

/* of the License, or (at your option) any later version.               */

/*                                                                      */

/* This program is distributed in the hope that it will be useful,      */

/* but WITHOUT ANY WARRANTY; without even the implied warranty of       */

/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */

/* GNU Library General Public License for more details.                 */

/* Semaphores a la POSIX 1003.1b */

#include <errno.h>

#include "pthread.h"

#include "internals.h"

#include "spinlock.h"

#include "restart.h"

#include "queue.h"

typedef struct {

    long int sem_status;

    int sem_spinlock;

} old_sem_t;

/* Maximum value the semaphore can have.  */

#define SEM_VALUE_MAX   ((int) ((~0u) >> 1))

static inline int sem_compare_and_swap(old_sem_t *sem, long oldval, long newval)

{

    return compare_and_swap(&sem->sem_status, oldval, newval, &sem->sem_spinlock);

}

/* The state of a semaphore is represented by a long int encoding

   either the semaphore count if >= 0 and no thread is waiting on it,

   or the head of the list of threads waiting for the semaphore.

   To distinguish the two cases, we encode the semaphore count N

   as 2N+1, so that it has the lowest bit set.

   A sequence of sem_wait operations on a semaphore initialized to N

   result in the following successive states:

     2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...

*/

static void sem_restart_list(pthread_descr waiting);

int __old_sem_init(old_sem_t *sem, int pshared, unsigned int value)

{

    if (value > SEM_VALUE_MAX) {

        errno = EINVAL;

        return -1;

    }

    if (pshared) {

        errno = ENOSYS;

        return -1;

    }

  sem->sem_spinlock = 0;

  sem->sem_status = ((long)value << 1) + 1;

  return 0;

}

/* Function called by pthread_cancel to remove the thread from

   waiting inside __old_sem_wait. Here we simply unconditionally

   indicate that the thread is to be woken, by returning 1. */

static int old_sem_extricate_func(void *obj, pthread_descr th)

{

    return 1;

}

int __old_sem_wait(old_sem_t * sem)

{

    long oldstatus, newstatus;

    volatile pthread_descr self = thread_self();

    pthread_descr * th;

    pthread_extricate_if extr;

    /* Set up extrication interface */

    extr.pu_object = 0;

    extr.pu_extricate_func = old_sem_extricate_func;

    while (1) {

        /* Register extrication interface */

        __pthread_set_own_extricate_if(self, &extr);

        do {

            oldstatus = sem->sem_status;

            if ((oldstatus & 1) && (oldstatus != 1))

                newstatus = oldstatus - 2;

            else {

                newstatus = (long) self;

                self->p_nextwaiting = (pthread_descr) oldstatus;

            }

        }

        while (! sem_compare_and_swap(sem, oldstatus, newstatus));

        if (newstatus & 1) {

            /* We got the semaphore. */

          __pthread_set_own_extricate_if(self, 0);

            return 0;

        }

        /* Wait for sem_post or cancellation */

        suspend(self);

        __pthread_set_own_extricate_if(self, 0);

        /* This is a cancellation point */

        if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {

            /* Remove ourselves from the waiting list if we're still on it */

            /* First check if we're at the head of the list. */

            do {

                oldstatus = sem->sem_status;

                if (oldstatus != (long) self) break;

                newstatus = (long) self->p_nextwaiting;

            }

            while (! sem_compare_and_swap(sem, oldstatus, newstatus));

            /* Now, check if we're somewhere in the list.

               There's a race condition with sem_post here, but it does not matter:

               the net result is that at the time pthread_exit is called,

               self is no longer reachable from sem->sem_status. */

            if (oldstatus != (long) self && (oldstatus & 1) == 0) {

                for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);

                     *th != NULL && *th != (pthread_descr) 1;

                     th = &((*th)->p_nextwaiting)) {

                    if (*th == self) {

                        *th = self->p_nextwaiting;

                        break;

                    }

                }

            }

            pthread_exit(PTHREAD_CANCELED);

        }

    }

}

int __old_sem_trywait(old_sem_t * sem)

{

  long oldstatus, newstatus;

  do {

    oldstatus = sem->sem_status;

    if ((oldstatus & 1) == 0 || (oldstatus == 1)) {

      errno = EAGAIN;

      return -1;

    }

    newstatus = oldstatus - 2;

  }

  while (! sem_compare_and_swap(sem, oldstatus, newstatus));

  return 0;

}

int __old_sem_post(old_sem_t * sem)

{

  long oldstatus, newstatus;

  do {

    oldstatus = sem->sem_status;

    if ((oldstatus & 1) == 0)

      newstatus = 3;

    else {

      if (oldstatus >= SEM_VALUE_MAX) {

        /* Overflow */

        errno = ERANGE;

        return -1;

      }

      newstatus = oldstatus + 2;

    }

  }

  while (! sem_compare_and_swap(sem, oldstatus, newstatus));

  if ((oldstatus & 1) == 0)

    sem_restart_list((pthread_descr) oldstatus);

  return 0;

}

int __old_sem_getvalue(old_sem_t * sem, int * sval)

{

  long status = sem->sem_status;

  if (status & 1)

    *sval = (int)((unsigned long) status >> 1);

  else

    *sval = 0;

  return 0;

}

int __old_sem_destroy(old_sem_t * sem)

{

  if ((sem->sem_status & 1) == 0) {

    errno = EBUSY;

    return -1;

  }

  return 0;

}

/* Auxiliary function for restarting all threads on a waiting list,

   in priority order. */

static void sem_restart_list(pthread_descr waiting)

{

  pthread_descr th, towake, *p;

  /* Sort list of waiting threads by decreasing priority (insertion sort) */

  towake = NULL;

  while (waiting != (pthread_descr) 1) {

    th = waiting;

    waiting = waiting->p_nextwaiting;

    p = &towake;

    while (*p != NULL && th->p_priority < (*p)->p_priority)

      p = &((*p)->p_nextwaiting);

    th->p_nextwaiting = *p;

    *p = th;

  }

  /* Wake up threads in priority order */

  while (towake != NULL) {

    th = towake;

    towake = towake->p_nextwaiting;

    th->p_nextwaiting = NULL;

    restart(th);

  }

}

#if defined __PIC__ && defined DO_VERSIONING

symbol_version (__old_sem_init, sem_init, GLIBC_2.0);

symbol_version (__old_sem_wait, sem_wait, GLIBC_2.0);

symbol_version (__old_sem_trywait, sem_trywait, GLIBC_2.0);

symbol_version (__old_sem_post, sem_post, GLIBC_2.0);

symbol_version (__old_sem_getvalue, sem_getvalue, GLIBC_2.0);

symbol_version (__old_sem_destroy, sem_destroy, GLIBC_2.0);

#endif