vcos/generic/vcos_generic_event_flags.c

/*
Copyright (c) 2012, Broadcom Europe Ltd
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
    * Neither the name of the copyright holder nor the
      names of its contributors may be used to endorse or promote products
      derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY
DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*=============================================================================
VideoCore OS Abstraction Layer - event flags implemented via mutexes
=============================================================================*/

#include "interface/vcos/vcos.h"
#include "interface/vcos/generic/vcos_generic_event_flags.h"

#include <stddef.h>

/** A structure created by a thread that waits on the event flags
  * for a particular combination of flags to arrive.
  */
typedef struct VCOS_EVENT_WAITER_T
{
   VCOS_UNSIGNED requested_events;  /**< The events wanted */
   VCOS_UNSIGNED actual_events;     /**< Actual events found */
   VCOS_UNSIGNED op;                /**< The event operation to be used */
   VCOS_STATUS_T return_status;     /**< The return status the waiter should pass back */
   VCOS_EVENT_FLAGS_T *flags;       /**< Pointer to the original 'flags' structure */
   VCOS_THREAD_T *thread;           /**< Thread waiting */
   struct VCOS_EVENT_WAITER_T *next;
} VCOS_EVENT_WAITER_T;

#ifndef NDEBUG
static int waiter_list_valid(VCOS_EVENT_FLAGS_T *flags);
#endif
static void event_flags_timer_expired(void *cxt);

VCOS_STATUS_T vcos_generic_event_flags_create(VCOS_EVENT_FLAGS_T *flags, const char *name)
{
   VCOS_STATUS_T rc;
   if ((rc=vcos_mutex_create(&flags->lock, name)) != VCOS_SUCCESS)
   {
      return rc;
   }

   flags->events = 0;
   flags->waiters.head = flags->waiters.tail = 0;
   return rc;
}

void vcos_generic_event_flags_set(VCOS_EVENT_FLAGS_T *flags,
                                  VCOS_UNSIGNED bitmask,
                                  VCOS_OPTION op)
{
   vcos_assert(flags);
   vcos_mutex_lock(&flags->lock);
   if (op == VCOS_OR)
   {
      flags->events |= bitmask;
   }
   else if (op == VCOS_AND)
   {
      flags->events &= bitmask;
   }
   else
   {
      vcos_assert(0);
   }

   /* Now wake up any threads that have now become signalled. */
   if (flags->waiters.head != NULL)
   {
      VCOS_UNSIGNED consumed_events = 0;
      VCOS_EVENT_WAITER_T **pcurrent_waiter = &flags->waiters.head;
      VCOS_EVENT_WAITER_T *prev_waiter = NULL;

      /* Walk the chain of tasks suspend on this event flag group to determine
       * if any of their requests can be satisfied.
       */
      while ((*pcurrent_waiter) != NULL)
      {
         VCOS_EVENT_WAITER_T *curr_waiter = *pcurrent_waiter;

         /* Determine if this request has been satisfied */

         /* First, find the event flags in common. */
         VCOS_UNSIGNED waiter_satisfied = flags->events & curr_waiter->requested_events;

         /* Second, determine if all the event flags must match */
         if (curr_waiter->op & VCOS_AND)
         {
            /* All requested events must be present */
            waiter_satisfied = (waiter_satisfied == curr_waiter->requested_events);
         }

         /* Wake this one up? */
         if (waiter_satisfied)
         {

            if (curr_waiter->op & VCOS_CONSUME)
            {
               consumed_events |= curr_waiter->requested_events;
            }

            /* remove this block from the list, taking care at the end */
            *pcurrent_waiter = curr_waiter->next;
            if (curr_waiter->next == NULL)
               flags->waiters.tail = prev_waiter;

            vcos_assert(waiter_list_valid(flags));

            curr_waiter->return_status = VCOS_SUCCESS;
            curr_waiter->actual_events = flags->events;

            _vcos_thread_sem_post(curr_waiter->thread);
         }
         else
         {
            /* move to next element in the list */
            prev_waiter = *pcurrent_waiter;
            pcurrent_waiter = &(curr_waiter->next);
         }
      }

      flags->events &= ~consumed_events;

   }

   vcos_mutex_unlock(&flags->lock);
}

void vcos_generic_event_flags_delete(VCOS_EVENT_FLAGS_T *flags)
{
   vcos_mutex_delete(&flags->lock);
}

extern VCOS_STATUS_T vcos_generic_event_flags_get(VCOS_EVENT_FLAGS_T *flags,
                                                  VCOS_UNSIGNED bitmask,
                                                  VCOS_OPTION op,
                                                  VCOS_UNSIGNED suspend,
                                                  VCOS_UNSIGNED *retrieved_bits)
{
   VCOS_EVENT_WAITER_T waitreq;
   VCOS_STATUS_T rc = VCOS_EAGAIN;
   int satisfied = 0;

   vcos_assert(flags);

   /* default retrieved bits to 0 */
   *retrieved_bits = 0;

   vcos_mutex_lock(&flags->lock);
   switch (op & VCOS_EVENT_FLAG_OP_MASK)
   {
   case VCOS_AND:
      if ((flags->events & bitmask) == bitmask)
      {
         *retrieved_bits = flags->events;
         rc = VCOS_SUCCESS;
         satisfied = 1;
         if (op & VCOS_CONSUME)
            flags->events &= ~bitmask;
      }
      break;

   case VCOS_OR:
      if (flags->events & bitmask)
      {
         *retrieved_bits = flags->events;
         rc = VCOS_SUCCESS;
         satisfied = 1;
         if (op & VCOS_CONSUME)
            flags->events &= ~bitmask;
      }
      break;

   default:
      vcos_assert(0);
      rc = VCOS_EINVAL;
      break;
   }

   if (!satisfied && suspend)
   {
      /* Have to go to sleep.
       *
       * Append to tail so we get FIFO ordering.
       */
      waitreq.requested_events = bitmask;
      waitreq.op = op;
      waitreq.return_status = VCOS_EAGAIN;
      waitreq.flags = flags;
      waitreq.actual_events = 0;
      waitreq.thread = vcos_thread_current();
      waitreq.next = 0;
      vcos_assert(waitreq.thread != (VCOS_THREAD_T*)-1);
      VCOS_QUEUE_APPEND_TAIL(&flags->waiters, &waitreq);

      if (suspend != (VCOS_UNSIGNED)-1)
         _vcos_task_timer_set(event_flags_timer_expired, &waitreq, suspend);

      vcos_mutex_unlock(&flags->lock);
      /* go to sleep and wait to be signalled or timeout */

      _vcos_thread_sem_wait();

      *retrieved_bits = waitreq.actual_events;
      rc = waitreq.return_status;

      /* cancel the timer - do not do this while holding the mutex as it
       * might be waiting for the timeout function to complete, which will
       * try to take the mutex.
       */
      if (suspend != (VCOS_UNSIGNED)-1)
         _vcos_task_timer_cancel();
   }
   else
   {
      vcos_mutex_unlock(&flags->lock);
   }

   return rc;
}

/** Called when a get call times out. Remove this thread's
  * entry from the waiting queue, then resume the thread.
  */
static void event_flags_timer_expired(void *cxt)
{
   VCOS_EVENT_WAITER_T *waitreq = (VCOS_EVENT_WAITER_T *)cxt;
   VCOS_EVENT_FLAGS_T *flags = waitreq->flags;
   VCOS_EVENT_WAITER_T **plist;
   VCOS_EVENT_WAITER_T *prev = NULL;
   VCOS_THREAD_T *thread = 0;

   vcos_assert(flags);

   vcos_mutex_lock(&flags->lock);

   /* walk the list of waiting threads on this event group, and remove
    * the one that has expired.
    *
    * FIXME: could use doubly-linked list if lots of threads are found
    * to be waiting on a single event flag instance.
    */
   plist = &flags->waiters.head;
   while (*plist != NULL)
   {
      if (*plist == waitreq)
      {
         int at_end;
         /* found it */
         thread = (*plist)->thread;
         at_end = ((*plist)->next == NULL);

         /* link past */
         *plist = (*plist)->next;
         if (at_end)
            flags->waiters.tail = prev;

         break;
      }
      prev = *plist;
      plist = &(*plist)->next;
   }
   vcos_assert(waiter_list_valid(flags));

   vcos_mutex_unlock(&flags->lock);

   if (thread)
   {
      _vcos_thread_sem_post(thread);
   }
}

#ifndef NDEBUG

static int waiter_list_valid(VCOS_EVENT_FLAGS_T *flags)
{
   int valid;
   /* Either both head and tail are NULL, or neither are NULL */
   if (flags->waiters.head == NULL)
   {
      valid = (flags->waiters.tail == NULL);
   }
   else
   {
      valid = (flags->waiters.tail != NULL);
   }

   /* If head and tail point at the same non-NULL element, then there
    * is only one element in the list.
    */
   if (flags->waiters.head && (flags->waiters.head == flags->waiters.tail))
   {
      valid = (flags->waiters.head->next == NULL);
   }
   return valid;
}

#endif