Memory pooling

[melted] / src / framework / mlt_pool.c

/*
 * mlt_pool.c -- memory pooling functionality
 * Copyright (C) 2003-2004 Ushodaya Enterprises Limited
 * Author: Charles Yates <charles.yates@pandora.be>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU 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 General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software Foundation,
 * Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include "mlt_properties.h"
#include "mlt_deque.h"

#include <stdlib.h>
#include <string.h>
#include <pthread.h>

/** Singleton repositories
*/

static mlt_properties pools = NULL;

/** Private pooling structure.
*/

typedef struct mlt_pool_s
{
        pthread_mutex_t lock;
        mlt_deque stack;
        int size;
}
*mlt_pool;

/** Private release structure
*/

typedef struct mlt_release_s
{
        void *ptr;
        mlt_pool pool;
}
*mlt_release;

/** Create a pool.
*/

static mlt_pool pool_init( int size )
{
        // Create the pool
        mlt_pool this = calloc( 1, sizeof( struct mlt_pool_s ) );

        // Initialise it
        if ( this != NULL )
        {
                // Initialise the mutex
                pthread_mutex_init( &this->lock, NULL );

                // Create the stack
                this->stack = mlt_deque_init( );

                // Assign the size
                this->size = size;
        }

        // Return it
        return this;
}

/** Get an item from the pool.
*/

static mlt_release pool_fetch( mlt_pool this )
{
        // We will generate a release object
        mlt_release release = NULL;

        // Sanity check
        if ( this != NULL )
        {
                // Lock the pool
                pthread_mutex_lock( &this->lock );

                // Check if the stack is empty
                if ( mlt_deque_count( this->stack ) != 0 )
                {
                        // Pop the top of the stack
                        release = mlt_deque_pop_back( this->stack );
                }
                else
                {
                        // We need to generate a release item
                        release = calloc( 1, sizeof( struct mlt_release_s ) );

                        // Initialise it
                        if ( release != NULL )
                        {
                                // Allocate the real memory
                                release->ptr = malloc( this->size );

                                // Assign the pool
                                release->pool = this;
                        }
                }

                // Unlock the pool
                pthread_mutex_unlock( &this->lock );
        }

        // Return the generated release object
        return release;
}

/** Return an item to the pool.
*/

static void pool_return( mlt_pool this, mlt_release that )
{
        // Sanity checks
        if ( this != NULL && that != NULL )
        {
                // Ensure that the pools match
                if ( this == that->pool )
                {
                        // Lock the pool
                        pthread_mutex_lock( &this->lock );

                        // Push the that back back on to the stack
                        mlt_deque_push_back( this->stack, that );

                        // Unlock the pool
                        pthread_mutex_unlock( &this->lock );

                        // Ensure that we don't clean up
                        that = NULL;
                }
        }

        // Tidy up - this will only occur if the returned item is incorrect
        if ( that != NULL )
        {
                // Free the memory
                free( that->ptr );

                // Free the release itself
                free( that );
        }
}

/** Destroy a pool.
*/

static void pool_close( mlt_pool this )
{
        if ( this != NULL )
        {
                // We need to free up all items in the pool
                mlt_release release = NULL;

                // Iterate through the stack until depleted
                while ( ( release = mlt_deque_pop_back( this->stack ) ) != NULL )
                {
                        // We'll return this item to NULL
                        pool_return( NULL, release );
                }

                // We can now close the stack
                mlt_deque_close( this->stack );

                // Destroy the mutex
                pthread_mutex_destroy( &this->lock );

                // Close the pool
                free( this );
        }
}

/** Initialise the pool.
*/

void mlt_pool_init( )
{
        // Loop variable used to create the pools
        int i = 0;

        // Create the pools
        pools = mlt_properties_new( );

        // Create the pools
        for ( i = 8; i < 32; i ++ )
        {
                // Each properties item needs a name
                char name[ 32 ];

                // Construct a pool
                mlt_pool pool = pool_init( 1 << i );

                // Generate a name
                sprintf( name, "%d", i );

                // Register with properties
                mlt_properties_set_data( pools, name, pool, 0, ( mlt_destructor )pool_close, NULL );
        }
}

/** Allocate size bytes from the pool.
*/

void *mlt_pool_allocate( int size, void **release )
{
        // This is the real release structure we'll return
        mlt_release real = NULL;

        // This will be used to obtain the pool to use
        mlt_pool pool = NULL;

        // Determines the index of the pool to use
        int index = 1;

        // Minimum size pooled is 256 bytes
        size = size >> 8;
        while ( ( 1 << index ) < size )
                index ++;

        // Now get the pool at the index
        pool = mlt_properties_get_data_at( pools, index + 1, NULL );

        // Now get the real item
        real = pool_fetch( pool );

        // Deal with return
        if ( real != NULL )
        {
                // Assign to release
                *release = real;

                // Return the pointer
                return real->ptr;
        }

        // Otherwise return a NULL to indicate failure
        return NULL;
}

/** Release the allocated memory.
*/

void mlt_pool_release( void *release )
{
        // Sanity check
        if ( release != NULL )
        {
                // Get the real release structure
                mlt_release real = release;

                // Return to the pool
                pool_return( real->pool, real );
        }
}

/** Close the pool.
*/

void mlt_pool_close( )
{
        // Close the properties
        mlt_properties_close( pools );
}