📄 tx_byts.c
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/**************************************************************************/
/* */
/* Copyright (c) 1996-2000 by Express Logic Inc. */
/* */
/* This software is copyrighted by and is the sole property of Express */
/* Logic, Inc. All rights, title, ownership, or other interests */
/* in the software remain the property of Express Logic, Inc. This */
/* software may only be used in accordance with the corresponding */
/* license agreement. Any unauthorized use, duplication, transmission, */
/* distribution, or disclosure of this software is expressly forbidden. */
/* */
/* This Copyright notice may not be removed or modified without prior */
/* written consent of Express Logic, Inc. */
/* */
/* Express Logic, Inc. reserves the right to modify this software */
/* without notice. */
/* */
/* Express Logic, Inc. */
/* 11440 West Bernardo Court info@expresslogic.com */
/* Suite 366 http://www.expresslogic.com */
/* San Diego, CA 92127 */
/* */
/**************************************************************************/
/**************************************************************************/
/**************************************************************************/
/** */
/** ThreadX Component */
/** */
/** Byte Pool (BYT) */
/** */
/**************************************************************************/
/**************************************************************************/
#define TX_SOURCE_CODE
/* Include necessary system files. */
#include "tx_api.h"
#include "tx_thr.h"
#include "tx_byt.h"
/**************************************************************************/
/* */
/* FUNCTION RELEASE */
/* */
/* _tx_byte_pool_search PORTABLE C */
/* 3.0f */
/* AUTHOR */
/* */
/* William E. Lamie, Express Logic, Inc. */
/* */
/* DESCRIPTION */
/* */
/* This function searches a byte pool for a memory block to satisfy */
/* the requested number of bytes. Merging of adjacent free blocks */
/* takes place during the search and a split of the block that */
/* satisfies the request may occur before this function returns. */
/* */
/* It is assumed that this function is called with interrupts enabled */
/* and with the tx_pool_owner field set to the thread performing the */
/* search. Also note that the search can occur during allocation and */
/* release of a memory block. */
/* */
/* INPUT */
/* */
/* pool_ptr Pointer to pool control block */
/* memory_size Number of bytes required */
/* */
/* OUTPUT */
/* */
/* CHAR_PTR Pointer to the allocated memory, */
/* if successful. Otherwise, a */
/* NULL is returned */
/* */
/* CALLS */
/* */
/* None */
/* */
/* CALLED BY */
/* */
/* _tx_byte_allocate Allocate bytes of memory */
/* _tx_byte_release Release bytes of memory */
/* */
/* RELEASE HISTORY */
/* */
/* DATE NAME DESCRIPTION */
/* */
/* 12-31-1996 William E. Lamie Initial Version 3.0 */
/* 11-11-1997 William E. Lamie Modified comment(s), */
/* resulting in version 3.0b. */
/* 01-01-1999 William E. Lamie Modified comment(s), */
/* resulting in version 3.0e. */
/* 11-01-1999 William E. Lamie Modified comment(s), */
/* resulting in version 3.0f. */
/* */
/**************************************************************************/
VOID *_tx_byte_pool_search(TX_BYTE_POOL *pool_ptr, ULONG memory_size)
{
TX_INTERRUPT_SAVE_AREA
REG_1 CHAR_PTR current_ptr; /* Current block pointer */
REG_2 CHAR_PTR next_ptr; /* Next block pointer */
REG_3 ULONG available_bytes; /* Calculate bytes available */
REG_4 ULONG examine_blocks; /* Blocks to be examined */
/* Disable interrupts. */
TX_DISABLE
/* First, determine if there are enough bytes in the pool. */
if (memory_size >= pool_ptr -> tx_byte_pool_available)
{
/* Restore interrupts. */
TX_RESTORE
/* Not enough memory, return a NULL pointer. */
return(TX_NULL);
}
/* Walk through the memory pool in search for a large enough block. */
current_ptr = pool_ptr -> tx_byte_pool_search;
examine_blocks = pool_ptr -> tx_byte_pool_fragments + 1;
available_bytes = 0;
do
{
/* Check to see if this block is free. */
if (*((ULONG *) (current_ptr + sizeof(CHAR_PTR))) == TX_BYTE_BLOCK_FREE)
{
/* Block is free, see if it is large enough. */
/* Pickup the next block's pointer. */
next_ptr = *((CHAR_PTR *) current_ptr);
/* Calculate the number of byte available in this block. */
available_bytes = next_ptr - current_ptr - sizeof(CHAR_PTR) - sizeof(ULONG);
/* If this is large enough, we are done because our first-fit algorithm
has been satisfied! */
if (available_bytes >= memory_size)
{
/* Get out of the search loop! */
break;
}
else
{
/* Clear the available bytes variable. */
available_bytes = 0;
/* Not enough memory, check to see if the neighbor is
free and can be merged. */
if (*((ULONG *) (next_ptr + sizeof(CHAR_PTR))) == TX_BYTE_BLOCK_FREE)
{
/* Yes, neighbor block can be merged! This is quickly accomplished
by updating the current block with the next blocks pointer. */
*((CHAR_PTR *) current_ptr) = *((CHAR_PTR *) next_ptr);
/* Reduce the fragment total. We don't need to increase the bytes
available because all free headers are also included in the available
count. */
pool_ptr -> tx_byte_pool_fragments--;
/* See if the search pointer is affected. */
if (pool_ptr -> tx_byte_pool_search == next_ptr)
pool_ptr -> tx_byte_pool_search = current_ptr;
}
else
{
/* Neighbor is not free so we can skip over it! */
current_ptr = *((CHAR_PTR *) next_ptr);
/* Decrement the examined block count to account for this one. */
if (examine_blocks)
examine_blocks--;
}
}
}
else
{
/* Block is not free, move to next block. */
current_ptr = *((CHAR_PTR *) current_ptr);
}
/* Another block has been searched... decrement counter. */
if (examine_blocks)
examine_blocks--;
/* Restore interrupts temporarily. */
TX_RESTORE
/* Disable interrupts. */
TX_DISABLE
/* Determine if anything has changed in terms of pool ownership. */
if (pool_ptr -> tx_byte_pool_owner != _tx_thread_current_ptr)
{
/* Pool changed ownership in the brief period interrupts were
enabled. Reset the search. */
current_ptr = pool_ptr -> tx_byte_pool_search;
examine_blocks = pool_ptr -> tx_byte_pool_fragments + 1;
/* Setup our ownership again. */
pool_ptr -> tx_byte_pool_owner = _tx_thread_current_ptr;
}
} while(examine_blocks);
/* Determine if a block was found. If so, determine if it needs to be
split. */
if (available_bytes)
{
/* Determine if we need to split this block. */
if ((available_bytes - memory_size) >= ((ULONG) TX_BYTE_BLOCK_MIN))
{
/* Split the block. */
next_ptr = current_ptr + memory_size + sizeof(CHAR_PTR) + sizeof(ULONG);
/* Setup the new free block. */
*((CHAR_PTR *) next_ptr) = *((CHAR_PTR *) current_ptr);
*((ULONG *) (next_ptr + sizeof(CHAR_PTR))) = TX_BYTE_BLOCK_FREE;
/* Increase the total fragment counter. */
pool_ptr -> tx_byte_pool_fragments++;
/* Update the current pointer to point at the newly created block. */
*((CHAR_PTR *) current_ptr) = next_ptr;
/* Set available equal to memory size for subsequent calculation. */
available_bytes = memory_size;
}
/* In any case, mark the current block as allocated. */
*((TX_BYTE_POOL **) (current_ptr + sizeof(CHAR_PTR))) = pool_ptr;
/* Reduce the number of available bytes in the pool. */
pool_ptr -> tx_byte_pool_available = pool_ptr -> tx_byte_pool_available -
available_bytes - sizeof(CHAR_PTR) - sizeof(ULONG);
/* Restore interrupts. */
TX_RESTORE
/* Adjust the pointer for the application. */
current_ptr = current_ptr + sizeof(CHAR_PTR) + sizeof(ULONG);
}
else
{
/* Restore interrupts. */
TX_RESTORE
/* Set current pointer to NULL to indicate nothing was found. */
current_ptr = TX_NULL;
}
/* Return the search pointer. */
return(current_ptr);
}
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