Logo Search packages:      
Sourcecode: glibc version File versions

aio_misc.c

/* Handle general operations.
   Copyright (C) 1997, 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <aio.h>
#include <assert.h>
#include <errno.h>
#include <limits.h>
#include <pthread.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/stat.h>
#include <sys/time.h>

#include "aio_misc.h"

static void add_request_to_runlist (struct requestlist *newrequest);

/* Pool of request list entries.  */
static struct requestlist **pool;

/* Number of total and allocated pool entries.  */
static size_t pool_max_size;
static size_t pool_size;

/* We implement a two dimensional array but allocate each row separately.
   The macro below determines how many entries should be used per row.
   It should better be a power of two.  */
#define ENTRIES_PER_ROW 32

/* How many rows we allocate at once.  */
#define ROWS_STEP 8

/* List of available entries.  */
static struct requestlist *freelist;

/* List of request waiting to be processed.  */
static struct requestlist *runlist;

/* Structure list of all currently processed requests.  */
static struct requestlist *requests;

/* Number of threads currently running.  */
static int nthreads;

/* Number of threads waiting for work to arrive. */
static int idle_thread_count;


/* These are the values used to optimize the use of AIO.  The user can
   overwrite them by using the `aio_init' function.  */
static struct aioinit optim =
{
  20, /* int aio_threads;     Maximal number of threads.  */
  64, /* int aio_num;         Number of expected simultanious requests. */
  0,
  0,
  0,
  0,
  1,
  0
};


/* Since the list is global we need a mutex protecting it.  */
pthread_mutex_t __aio_requests_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;

/* When you add a request to the list and there are idle threads present,
   you signal this condition variable. When a thread finishes work, it waits
   on this condition variable for a time before it actually exits. */
pthread_cond_t __aio_new_request_notification = PTHREAD_COND_INITIALIZER;


/* Functions to handle request list pool.  */
static struct requestlist *
get_elem (void)
{
  struct requestlist *result;

  if (freelist == NULL)
    {
      struct requestlist *new_row;
      int cnt;

      assert (sizeof (struct aiocb) == sizeof (struct aiocb64));

      if (pool_size + 1 >= pool_max_size)
      {
        size_t new_max_size = pool_max_size + ROWS_STEP;
        struct requestlist **new_tab;

        new_tab = (struct requestlist **)
          realloc (pool, new_max_size * sizeof (struct requestlist *));

        if (new_tab == NULL)
          return NULL;

        pool_max_size = new_max_size;
        pool = new_tab;
      }

      /* Allocate the new row.  */
      cnt = pool_size == 0 ? optim.aio_num : ENTRIES_PER_ROW;
      new_row = (struct requestlist *) calloc (cnt,
                                     sizeof (struct requestlist));
      if (new_row == NULL)
      return NULL;

      pool[pool_size++] = new_row;

      /* Put all the new entries in the freelist.  */
      do
      {
        new_row->next_prio = freelist;
        freelist = new_row++;
      }
      while (--cnt > 0);
    }

  result = freelist;
  freelist = freelist->next_prio;

  return result;
}


void
internal_function
__aio_free_request (struct requestlist *elem)
{
  elem->running = no;
  elem->next_prio = freelist;
  freelist = elem;
}


struct requestlist *
internal_function
__aio_find_req (aiocb_union *elem)
{
  struct requestlist *runp = requests;
  int fildes = elem->aiocb.aio_fildes;

  while (runp != NULL && runp->aiocbp->aiocb.aio_fildes < fildes)
    runp = runp->next_fd;

  if (runp != NULL)
    {
      if (runp->aiocbp->aiocb.aio_fildes != fildes)
      runp = NULL;
      else
      while (runp != NULL && runp->aiocbp != elem)
        runp = runp->next_prio;
    }

  return runp;
}


struct requestlist *
internal_function
__aio_find_req_fd (int fildes)
{
  struct requestlist *runp = requests;

  while (runp != NULL && runp->aiocbp->aiocb.aio_fildes < fildes)
    runp = runp->next_fd;

  return (runp != NULL && runp->aiocbp->aiocb.aio_fildes == fildes
        ? runp : NULL);
}


void
internal_function
__aio_remove_request (struct requestlist *last, struct requestlist *req,
                  int all)
{
  assert (req->running == yes || req->running == queued
        || req->running == done);

  if (last != NULL)
    last->next_prio = all ? NULL : req->next_prio;
  else
    {
      if (all || req->next_prio == NULL)
      {
        if (req->last_fd != NULL)
          req->last_fd->next_fd = req->next_fd;
        else
          requests = req->next_fd;
        if (req->next_fd != NULL)
          req->next_fd->last_fd = req->last_fd;
      }
      else
      {
        if (req->last_fd != NULL)
          req->last_fd->next_fd = req->next_prio;
        else
          requests = req->next_prio;

        if (req->next_fd != NULL)
          req->next_fd->last_fd = req->next_prio;

        req->next_prio->last_fd = req->last_fd;
        req->next_prio->next_fd = req->next_fd;

        /* Mark this entry as runnable.  */
        req->next_prio->running = yes;
      }

      if (req->running == yes)
      {
        struct requestlist *runp = runlist;

        last = NULL;
        while (runp != NULL)
          {
            if (runp == req)
            {
              if (last == NULL)
                runlist = runp->next_run;
              else
                last->next_run = runp->next_run;
              break;
            }
            last = runp;
            runp = runp->next_run;
          }
      }
    }
}


/* The thread handler.  */
static void *handle_fildes_io (void *arg);


/* User optimization.  */
void
__aio_init (const struct aioinit *init)
{
  /* Get the mutex.  */
  pthread_mutex_lock (&__aio_requests_mutex);

  /* Only allow writing new values if the table is not yet allocated.  */
  if (pool == NULL)
    {
      optim.aio_threads = init->aio_threads < 1 ? 1 : init->aio_threads;
      optim.aio_num = (init->aio_num < ENTRIES_PER_ROW
                   ? ENTRIES_PER_ROW
                   : init->aio_num & ~ENTRIES_PER_ROW);
    }

  if (init->aio_idle_time != 0)
    optim.aio_idle_time = init->aio_idle_time;

  /* Release the mutex.  */
  pthread_mutex_unlock (&__aio_requests_mutex);
}
weak_alias (__aio_init, aio_init)


/* The main function of the async I/O handling.  It enqueues requests
   and if necessary starts and handles threads.  */
struct requestlist *
internal_function
__aio_enqueue_request (aiocb_union *aiocbp, int operation)
{
  int result = 0;
  int policy, prio;
  struct sched_param param;
  struct requestlist *last, *runp, *newp;
  int running = no;

  if (operation == LIO_SYNC || operation == LIO_DSYNC)
    aiocbp->aiocb.aio_reqprio = 0;
  else if (aiocbp->aiocb.aio_reqprio < 0
         || aiocbp->aiocb.aio_reqprio > AIO_PRIO_DELTA_MAX)
    {
      /* Invalid priority value.  */
      __set_errno (EINVAL);
      aiocbp->aiocb.__error_code = EINVAL;
      aiocbp->aiocb.__return_value = -1;
      return NULL;
    }

  /* Compute priority for this request.  */
  pthread_getschedparam (pthread_self (), &policy, &param);
  prio = param.sched_priority - aiocbp->aiocb.aio_reqprio;

  /* Get the mutex.  */
  pthread_mutex_lock (&__aio_requests_mutex);

  last = NULL;
  runp = requests;
  /* First look whether the current file descriptor is currently
     worked with.  */
  while (runp != NULL
       && runp->aiocbp->aiocb.aio_fildes < aiocbp->aiocb.aio_fildes)
    {
      last = runp;
      runp = runp->next_fd;
    }

  /* Get a new element for the waiting list.  */
  newp = get_elem ();
  if (newp == NULL)
    {
      pthread_mutex_unlock (&__aio_requests_mutex);
      __set_errno (EAGAIN);
      return NULL;
    }
  newp->aiocbp = aiocbp;
  newp->caller_pid = (aiocbp->aiocb.aio_sigevent.sigev_notify == SIGEV_SIGNAL
                  ? getpid () : 0);
  newp->waiting = NULL;

  aiocbp->aiocb.__abs_prio = prio;
  aiocbp->aiocb.__policy = policy;
  aiocbp->aiocb.aio_lio_opcode = operation;
  aiocbp->aiocb.__error_code = EINPROGRESS;
  aiocbp->aiocb.__return_value = 0;

  if (runp != NULL
      && runp->aiocbp->aiocb.aio_fildes == aiocbp->aiocb.aio_fildes)
    {
      /* The current file descriptor is worked on.  It makes no sense
       to start another thread since this new thread would fight
       with the running thread for the resources.  But we also cannot
       say that the thread processing this desriptor shall immediately
       after finishing the current job process this request if there
       are other threads in the running queue which have a higher
       priority.  */

      /* Simply enqueue it after the running one according to the
       priority.  */
      while (runp->next_prio != NULL
           && runp->next_prio->aiocbp->aiocb.__abs_prio >= prio)
      runp = runp->next_prio;

      newp->next_prio = runp->next_prio;
      runp->next_prio = newp;

      running = queued;
    }
  else
    {
      running = yes;
      /* Enqueue this request for a new descriptor.  */
      if (last == NULL)
      {
        newp->last_fd = NULL;
        newp->next_fd = requests;
        if (requests != NULL)
          requests->last_fd = newp;
        requests = newp;
      }
      else
      {
        newp->next_fd = last->next_fd;
        newp->last_fd = last;
        last->next_fd = newp;
        if (newp->next_fd != NULL)
          newp->next_fd->last_fd = newp;
      }

      newp->next_prio = NULL;
    }

  if (running == yes)
    {
      /* We try to create a new thread for this file descriptor.  The
       function which gets called will handle all available requests
       for this descriptor and when all are processed it will
       terminate.

       If no new thread can be created or if the specified limit of
       threads for AIO is reached we queue the request.  */

      /* See if we need to and are able to create a thread.  */
      if (nthreads < optim.aio_threads && idle_thread_count == 0)
      {
        pthread_t thid;
        pthread_attr_t attr;

        /* Make sure the thread is created detached.  */
        pthread_attr_init (&attr);
        pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);

        running = newp->running = allocated;

        /* Now try to start a thread.  */
        if (pthread_create (&thid, &attr, handle_fildes_io, newp) == 0)
          /* We managed to enqueue the request.  All errors which can
             happen now can be recognized by calls to `aio_return' and
             `aio_error'.  */
          ++nthreads;
        else
          {
            /* Reset the running flag.  The new request is not running.  */
            running = newp->running = yes;

            if (nthreads == 0)
            /* We cannot create a thread in the moment and there is
               also no thread running.  This is a problem.  `errno' is
               set to EAGAIN if this is only a temporary problem.  */
            result = -1;
          }
      }
    }

  /* Enqueue the request in the run queue if it is not yet running.  */
  if (running == yes && result == 0)
    {
      add_request_to_runlist (newp);

      /* If there is a thread waiting for work, then let it know that we
       have just given it something to do. */
      if (idle_thread_count > 0)
      pthread_cond_signal (&__aio_new_request_notification);
    }

  if (result == 0)
    newp->running = running;
  else
    {
      /* Something went wrong.  */
      __aio_free_request (newp);
      newp = NULL;
    }

  /* Release the mutex.  */
  pthread_mutex_unlock (&__aio_requests_mutex);

  return newp;
}


static void *
__attribute__ ((noreturn))
handle_fildes_io (void *arg)
{
  pthread_t self = pthread_self ();
  struct sched_param param;
  struct requestlist *runp = (struct requestlist *) arg;
  aiocb_union *aiocbp;
  int policy;
  int fildes;

  pthread_getschedparam (self, &policy, &param);

  do
    {
      /* If runp is NULL, then we were created to service the work queue
       in general, not to handle any particular request. In that case we
       skip the "do work" stuff on the first pass, and go directly to the
       "get work off the work queue" part of this loop, which is near the
       end. */
      if (runp == NULL)
      pthread_mutex_lock (&__aio_requests_mutex);
      else
      {
        /* Hopefully this request is marked as running.  */
        assert (runp->running == allocated);

        /* Update our variables.  */
        aiocbp = runp->aiocbp;
        fildes = aiocbp->aiocb.aio_fildes;

        /* Change the priority to the requested value (if necessary).  */
        if (aiocbp->aiocb.__abs_prio != param.sched_priority
            || aiocbp->aiocb.__policy != policy)
          {
            param.sched_priority = aiocbp->aiocb.__abs_prio;
            policy = aiocbp->aiocb.__policy;
            pthread_setschedparam (self, policy, &param);
          }

        /* Process request pointed to by RUNP.  We must not be disturbed
           by signals.  */
        if ((aiocbp->aiocb.aio_lio_opcode & 127) == LIO_READ)
          {
            if (aiocbp->aiocb.aio_lio_opcode & 128)
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (__pread64 (fildes, (void *)
                                     aiocbp->aiocb64.aio_buf,
                                     aiocbp->aiocb64.aio_nbytes,
                                     aiocbp->aiocb64.aio_offset));
            else
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (pread (fildes,
                                   (void *) aiocbp->aiocb.aio_buf,
                                   aiocbp->aiocb.aio_nbytes,
                                   aiocbp->aiocb.aio_offset));

            if (aiocbp->aiocb.__return_value == -1 && errno == ESPIPE)
            /* The Linux kernel is different from others.  It returns
               ESPIPE if using pread on a socket.  Other platforms
               simply ignore the offset parameter and behave like
               read.  */
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (read (fildes,
                                  (void *) aiocbp->aiocb64.aio_buf,
                                  aiocbp->aiocb64.aio_nbytes));
          }
        else if ((aiocbp->aiocb.aio_lio_opcode & 127) == LIO_WRITE)
          {
            if (aiocbp->aiocb.aio_lio_opcode & 128)
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (__pwrite64 (fildes, (const void *)
                                      aiocbp->aiocb64.aio_buf,
                                      aiocbp->aiocb64.aio_nbytes,
                                      aiocbp->aiocb64.aio_offset));
            else
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (__libc_pwrite (fildes, (const void *)
                                    aiocbp->aiocb.aio_buf,
                                    aiocbp->aiocb.aio_nbytes,
                                    aiocbp->aiocb.aio_offset));

            if (aiocbp->aiocb.__return_value == -1 && errno == ESPIPE)
            /* The Linux kernel is different from others.  It returns
               ESPIPE if using pwrite on a socket.  Other platforms
               simply ignore the offset parameter and behave like
               write.  */
            aiocbp->aiocb.__return_value =
              TEMP_FAILURE_RETRY (write (fildes,
                                   (void *) aiocbp->aiocb64.aio_buf,
                                   aiocbp->aiocb64.aio_nbytes));
          }
        else if (aiocbp->aiocb.aio_lio_opcode == LIO_DSYNC)
          aiocbp->aiocb.__return_value =
            TEMP_FAILURE_RETRY (fdatasync (fildes));
        else if (aiocbp->aiocb.aio_lio_opcode == LIO_SYNC)
          aiocbp->aiocb.__return_value =
            TEMP_FAILURE_RETRY (fsync (fildes));
        else
          {
            /* This is an invalid opcode.  */
            aiocbp->aiocb.__return_value = -1;
            __set_errno (EINVAL);
          }

        /* Get the mutex.  */
        pthread_mutex_lock (&__aio_requests_mutex);

        /* In theory we would need here a write memory barrier since the
           callers test using aio_error() whether the request finished
           and once this value != EINPROGRESS the field __return_value
           must be committed to memory.

           But since the pthread_mutex_lock call involves write memory
           barriers as well it is not necessary.  */

        if (aiocbp->aiocb.__return_value == -1)
          aiocbp->aiocb.__error_code = errno;
        else
          aiocbp->aiocb.__error_code = 0;

        /* Send the signal to notify about finished processing of the
           request.  */
        __aio_notify (runp);

        /* For debugging purposes we reset the running flag of the
           finished request.  */
        assert (runp->running == allocated);
        runp->running = done;

        /* Now dequeue the current request.  */
        __aio_remove_request (NULL, runp, 0);
        if (runp->next_prio != NULL)
          add_request_to_runlist (runp->next_prio);

        /* Free the old element.  */
        __aio_free_request (runp);
      }

      runp = runlist;

      /* If the runlist is empty, then we sleep for a while, waiting for
       something to arrive in it. */
      if (runp == NULL && optim.aio_idle_time >= 0)
      {
        struct timeval now;
        struct timespec wakeup_time;

        ++idle_thread_count;
        gettimeofday (&now, NULL);
        wakeup_time.tv_sec = now.tv_sec + optim.aio_idle_time;
        wakeup_time.tv_nsec = now.tv_usec * 1000;
        if (wakeup_time.tv_nsec > 1000000000)
          {
            wakeup_time.tv_nsec -= 1000000000;
            ++wakeup_time.tv_sec;
          }
        pthread_cond_timedwait (&__aio_new_request_notification,
                          &__aio_requests_mutex,
                          &wakeup_time);
        --idle_thread_count;
        runp = runlist;
      }

      if (runp == NULL)
      --nthreads;
      else
      {
        assert (runp->running == yes);
        runp->running = allocated;
        runlist = runp->next_run;

        /* If we have a request to process, and there's still another in
           the run list, then we need to either wake up or create a new
           thread to service the request that is still in the run list. */
        if (runlist != NULL)
          {
            /* There are at least two items in the work queue to work on.
             If there are other idle threads, then we should wake them
             up for these other work elements; otherwise, we should try
             to create a new thread. */
            if (idle_thread_count > 0)
            pthread_cond_signal (&__aio_new_request_notification);
            else if (nthreads < optim.aio_threads)
            {
              pthread_t thid;
              pthread_attr_t attr;

              /* Make sure the thread is created detached.  */
              pthread_attr_init (&attr);
              pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);

              /* Now try to start a thread. If we fail, no big deal,
                 because we know that there is at least one thread (us)
                 that is working on AIO operations. */
              if (pthread_create (&thid, &attr, handle_fildes_io, NULL)
                  == 0)
                ++nthreads;
            }
          }
      }

      /* Release the mutex.  */
      pthread_mutex_unlock (&__aio_requests_mutex);
    }
  while (runp != NULL);

  pthread_exit (NULL);
}


/* Free allocated resources.  */
libc_freeres_fn (free_res)
{
  size_t row;

  for (row = 0; row < pool_max_size; ++row)
    free (pool[row]);

  free (pool);
}


/* Add newrequest to the runlist. The __abs_prio flag of newrequest must
   be correctly set to do this. Also, you had better set newrequest's
   "running" flag to "yes" before you release your lock or you'll throw an
   assertion. */
static void
add_request_to_runlist (struct requestlist *newrequest)
{
  int prio = newrequest->aiocbp->aiocb.__abs_prio;
  struct requestlist *runp;

  if (runlist == NULL || runlist->aiocbp->aiocb.__abs_prio < prio)
    {
      newrequest->next_run = runlist;
      runlist = newrequest;
    }
  else
    {
      runp = runlist;

      while (runp->next_run != NULL
           && runp->next_run->aiocbp->aiocb.__abs_prio >= prio)
      runp = runp->next_run;

      newrequest->next_run = runp->next_run;
      runp->next_run = newrequest;
    }
}

Generated by  Doxygen 1.6.0   Back to index