CoreFoundation/examples/Allocator/AllocatorExample.c

/*
 Simple CFAllocator example program, demonstrating creation and use of custom CFAllocators.
 Author: Ali Ozer
 7/7/99

 Copyright (c) 1999-2004, Apple Computer, Inc., all rights reserved.
*/
/*
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*/
#include <CoreFoundation/CoreFoundation.h>
#include <stdio.h>
#include <stdlib.h>


// This function will print the provided arguments (printf style varargs) out to the console.
// Note that the CFString formatting function accepts "%@" as a way to display CF types.
// For types other than CFString and CFNumber, the result of %@ is mostly for debugging
// and can differ between releases and different platforms.

void show(CFStringRef formatString, ...) {
    CFStringRef resultString;
    CFDataRef data;
    va_list argList;

    va_start(argList, formatString);
    resultString = CFStringCreateWithFormatAndArguments(NULL, NULL, formatString, argList);
    va_end(argList);

    data = CFStringCreateExternalRepresentation(NULL, resultString, CFStringGetSystemEncoding(), '?');

    if (data != NULL) {
    	printf ("%.*s\n\n", (int)CFDataGetLength(data), CFDataGetBytePtr(data));
    	CFRelease(data);
    }
       
    CFRelease(resultString);
}


// "Counting" Allocator
// A simple custom allocator that will count memory allocations and place guards to check memory corruption.

void verifyMemory(int *ptr) {
    int size = ptr[0];
    if (ptr[1] != 0x42424242) abort();
    if (ptr[2 + size / sizeof(int)] != 0x42424242) abort();
    if (ptr[2 + size / sizeof(int) + 1] != 0x42424242) abort();
    if (ptr[2 + size / sizeof(int) + 2] != 0x42424242) abort();
    if (ptr[2 + size / sizeof(int) + 3] != 0x42424242) abort();
}

static void *countingRealloc(void *oPtr, CFIndex size, CFOptionFlags hint, void *info) {
    int *ptr = (int*)oPtr;

    // Round it up to int alignment.
    size = ((size + sizeof(int) - 1) / sizeof(int)) * sizeof(int);

    if (ptr) {
        ptr = ptr - 2;	// Get back to the the originally allocated piece
        verifyMemory(ptr);
        ptr = (int*)realloc(ptr, size + sizeof(int) * 6);
    } else {
        ptr = (int*)malloc(size + sizeof(int) * 6);
    }
    ptr[0] = size;	// Doesn't include the guards
    ptr[1] = 0x42424242;
    ptr[2 + size / sizeof(int)] = 0x42424242;
    ptr[2 + size / sizeof(int) + 1] = 0x42424242;
    ptr[2 + size / sizeof(int) + 2] = 0x42424242;
    ptr[2 + size / sizeof(int) + 3] = 0x42424242;

    return (void *)(ptr + 2);
}

static void *countingAlloc(CFIndex size, CFOptionFlags hint, void *info) {
    (*(int *)info)++;		// Increment count
    return countingRealloc(NULL, size, hint, info);
}

static void countingDealloc(void *ptr, void *info) {
    (*(int *)info)--;		// Decrement count
    ptr = (int *)ptr - 2;	// Restore pointer to the actual malloc block
    verifyMemory((int*)ptr);
    free(ptr);
}

// Returns info about the number of outstanding allocations

static CFIndex NumOutstandingAllocations(CFAllocatorRef alloc) {
    CFAllocatorContext context;
    context.version = 0;
    CFAllocatorGetContext(alloc, &context);
    return (*(int *)(context.info));
}

// Creates a "counting allocator" --- keeps track of number of
// outstanding allocations and also uses guards to catch out of bound writes

static CFAllocatorRef CreateCountingAllocator(CFAllocatorRef alloc) {
    CFAllocatorContext context = {0, NULL, NULL, (CFAllocatorReleaseCallBack)free, NULL, countingAlloc, countingRealloc, countingDealloc, NULL};
    context.info = malloc(sizeof(int));
    // The info field points to an int which keeps number of allocations/deallocations
    // The "free" in slot 3 of the context assures the info field is properly freed when the allocator is
    *(int *)(context.info) = 0;
    // Create and return the allocator
    return CFAllocatorCreate(alloc, &context);
}



// "Reduced Malloc" Allocator
// A simple custom allocator that tries to avoid allocations.
// This allocator will allocate one chunk of memory containing n blocks of a certain size each,
// and manage these as the memory pool. If larger requests or more requests come in, this
// allocator will fall back on allocating actual memory.
// Note: This allocator isn't that great; it's provided as sample code only.

// This struct holds the actual blocks for the memory plus the necessary info
// (The allocated size of this struct will depend on the desired number of blocks)

typedef struct {
    CFAllocatorRef allocator;
    CFIndex size;
    CFIndex numBlocks;
    CFIndex firstAvailable;
    CFIndex numAdditionalAllocations;	// Stats for finding out how much addt'l memory was allocated
    void *mem[0];
} rmInfo;

// This function is used to free the above structure when the allocator is deallocated

void rmInfoFree(const void *actualInfo) {
    rmInfo *info = (rmInfo *)actualInfo;
    CFAllocatorRef allocator = info->allocator;
    CFAllocatorDeallocate(allocator, info);
    CFRelease(allocator);
}

#define rmNextBlockNum(info, blockNum) *(int *)(((unsigned char *)&(info->mem)) + (blockNum * info->size))
// #define rmBlock(info, blockNum) ((&(info->mem)) + (blockNum * info->size))
#define rmBlock(info, blockNum) (((unsigned char *)&(info->mem)) + (blockNum * info->size))
#define rmBlockNumber(info, ptr) (((unsigned char *)ptr - (unsigned char *)rmBlock(info, 0)) / info->size)
#define isRMBlock(info, ptr) (ptr >= (void *)rmBlock(info, 0) && ptr <= (void *)rmBlock(info, info->numBlocks))

static void rmMarkBlockAsAvailable(rmInfo *info, CFIndex blockNum) {
    // Put this block at the head of the available list
    rmNextBlockNum(info, blockNum) = info->firstAvailable;
    info->firstAvailable = blockNum;
}

static void rmMarkFirstAvailableAsUnavailable(rmInfo *info) {
    // This will only happen for the first block, so take it off the free list and return
    info->firstAvailable = rmNextBlockNum(info, info->firstAvailable);
}

// The function pointers for the allocator context

static void *rmRealloc(void *oPtr, CFIndex size, CFOptionFlags hint, void *actualInfo) {
    rmInfo *info = (rmInfo *)actualInfo;
    if (isRMBlock(info, oPtr)) {
	void *ptr;
        if (size <= info->size) return oPtr;	// Easy case...
	ptr = CFAllocatorAllocate(info->allocator, size, hint);
	memmove(ptr, oPtr, info->size);
	rmMarkBlockAsAvailable(info, rmBlockNumber(info, oPtr));
	info->numAdditionalAllocations++;
	return ptr;
    } else {
	return CFAllocatorReallocate(info->allocator, oPtr, size, hint);
    }
}

static void *rmAlloc(CFIndex size, CFOptionFlags hint, void *actualInfo) {
    rmInfo *info = (rmInfo *)actualInfo;
    if ((info->firstAvailable == -1) || (size > info->size)) {
	// No more available; allocate addt'l memory
	info->numAdditionalAllocations++;
        return CFAllocatorAllocate(info->allocator, size, hint);
    } else {
	void *ptr = rmBlock(info, info->firstAvailable);
	rmMarkFirstAvailableAsUnavailable(info);
        return ptr;
    }
}

static void rmDealloc(void *ptr, void *actualInfo) {
    rmInfo *info = (rmInfo *)actualInfo;
    if (isRMBlock(info, ptr)) {
	// It is one of ours, so mark it as available
	rmMarkBlockAsAvailable(info, rmBlockNumber(info, ptr));
    } else {
	// It is not, so directly deallocate
	info->numAdditionalAllocations--;
        CFAllocatorDeallocate(info->allocator, ptr);
    }
}

static CFIndex NumAdditionalAllocations(CFAllocatorRef alloc) {
    CFAllocatorContext context;
    context.version = 0;
    CFAllocatorGetContext(alloc, &context);
    return ((rmInfo *)(context.info))->numAdditionalAllocations;
}

// Creates a "reduced malloc allocator".

static CFAllocatorRef CreateReducedMallocAllocator(CFAllocatorRef alloc, CFIndex size, CFIndex numBlocks) {
    CFIndex cnt;
    rmInfo *info;
    CFAllocatorContext context = {0, NULL, NULL, rmInfoFree, NULL, rmAlloc, rmRealloc, rmDealloc, NULL};

    // Create and initialize the info block and the memory
    info = (rmInfo*)CFAllocatorAllocate(alloc, (sizeof(rmInfo) + size * numBlocks), 0);
    info->size = size;
    info->numBlocks = numBlocks;
    info->firstAvailable = -1;
    info->numAdditionalAllocations = 0;
    for (cnt = 0; cnt < numBlocks; cnt++) rmMarkBlockAsAvailable(info, cnt);
    // Retain the allocator used to allocate the memory
    info->allocator = (CFAllocatorRef)((alloc) ? CFRetain(alloc) : CFRetain(CFAllocatorGetDefault()));
    // And hang on to the info block
    context.info = info;
    // Finally, create and return the allocator
    return CFAllocatorCreate(alloc, &context);
}



// Now some example code which uses these allocators

void countingAllocatorExample(void) {

    CFStringRef str1, str2, str3;
    CFMutableStringRef mStr;

    CFAllocatorRef countingAllocator;

    show(CFSTR("Counting Allocator Test"));

    countingAllocator = CreateCountingAllocator(NULL);

    show(CFSTR("At start, number of allocations: %d"), NumOutstandingAllocations(countingAllocator));

    str1 = CFStringCreateWithCString(countingAllocator, "Hello World", kCFStringEncodingASCII);
#if defined(__APPLE__)
    str2 = CFStringCreateWithPascalString(countingAllocator, "\pHello World", kCFStringEncodingASCII);
#else
    str2 = CFStringCreateWithCString(countingAllocator, "Hello World", kCFStringEncodingASCII);
#endif
    mStr = CFStringCreateMutableCopy(countingAllocator, 0, str1);
    str3 = CFStringCreateCopy(countingAllocator, mStr);

    show(CFSTR("After creation, number of allocations: %d"), NumOutstandingAllocations(countingAllocator));

    CFStringAppend(mStr, str1);
    CFStringAppend(mStr, str1);
    CFStringAppend(mStr, str1);

    show(CFSTR("After mutations, number of allocations: %d"), NumOutstandingAllocations(countingAllocator));

    CFRelease(str1);
    CFRelease(str2);
    CFRelease(mStr);
    CFRelease(str3);

    show(CFSTR("After releasing, number of allocations: %d"), NumOutstandingAllocations(countingAllocator));

    CFRelease(countingAllocator);
}


void reducedMallocAllocatorExample(void) {

    CFStringRef str1, str2, str3;
    CFMutableStringRef mStr;

    CFAllocatorRef reducedMallocAllocator;

    show(CFSTR("Reduced Malloc Allocator Test"));

    // Create a reduced memory allocator; have it start with 3 blocks of 40 bytes each.

    reducedMallocAllocator = CreateReducedMallocAllocator(NULL, 40, 3);

    show(CFSTR("At start, number of addt'l allocations: %d"), NumAdditionalAllocations(reducedMallocAllocator));

    str1 = CFStringCreateWithCString(reducedMallocAllocator, "Hello World", kCFStringEncodingASCII);
#if defined(__APPLE__)
    str2 = CFStringCreateWithPascalString(reducedMallocAllocator, "\pHello World", kCFStringEncodingASCII);
#else
    str2 = CFStringCreateWithCString(reducedMallocAllocator, "Hello World", kCFStringEncodingASCII);
#endif
    mStr = CFStringCreateMutableCopy(reducedMallocAllocator, 0, str1);
    str3 = CFStringCreateCopy(reducedMallocAllocator, mStr);

    show(CFSTR("After creation, number of addt'l allocations: %d"), NumAdditionalAllocations(reducedMallocAllocator));

    CFStringAppend(mStr, str1);
    CFStringAppend(mStr, str1);
    CFStringAppend(mStr, str1);

    show(CFSTR("After mutations, number of addt'l allocations: %d"), NumAdditionalAllocations(reducedMallocAllocator));

    CFRelease(str1);
    CFRelease(str2);
    CFRelease(mStr);
    CFRelease(str3);

    show(CFSTR("After releasing, number of addt'l allocations: %d"), NumAdditionalAllocations(reducedMallocAllocator));

    CFRelease(reducedMallocAllocator);
}


int main (int argc, const char *argv[]) {
    countingAllocatorExample();
    reducedMallocAllocatorExample();

    return 0;
}