factor/vm/code_gc.cpp

342 lines
7.4 KiB
C++
Executable File

#include "master.hpp"
namespace factor
{
static void clear_free_list(heap *heap)
{
memset(&heap->free,0,sizeof(heap_free_list));
}
/* This malloc-style heap code is reasonably generic. Maybe in the future, it
will be used for the data heap too, if we ever get incremental
mark/sweep/compact GC. */
void new_heap(heap *heap, cell size)
{
heap->seg = alloc_segment(align_page(size));
if(!heap->seg)
fatal_error("Out of memory in new_heap",size);
clear_free_list(heap);
}
static void add_to_free_list(heap *heap, free_heap_block *block)
{
if(block->size < free_list_count * block_size_increment)
{
int index = block->size / block_size_increment;
block->next_free = heap->free.small_blocks[index];
heap->free.small_blocks[index] = block;
}
else
{
block->next_free = heap->free.large_blocks;
heap->free.large_blocks = block;
}
}
/* Called after reading the code heap from the image file, and after code GC.
In the former case, we must add a large free block from compiling.base + size to
compiling.limit. */
void build_free_list(heap *heap, cell size)
{
heap_block *prev = NULL;
clear_free_list(heap);
size = (size + block_size_increment - 1) & ~(block_size_increment - 1);
heap_block *scan = first_block(heap);
free_heap_block *end = (free_heap_block *)(heap->seg->start + size);
/* Add all free blocks to the free list */
while(scan && scan < (heap_block *)end)
{
switch(scan->status)
{
case B_FREE:
add_to_free_list(heap,(free_heap_block *)scan);
break;
case B_ALLOCATED:
break;
default:
critical_error("Invalid scan->status",(cell)scan);
break;
}
prev = scan;
scan = next_block(heap,scan);
}
/* If there is room at the end of the heap, add a free block. This
branch is only taken after loading a new image, not after code GC */
if((cell)(end + 1) <= heap->seg->end)
{
end->status = B_FREE;
end->size = heap->seg->end - (cell)end;
/* add final free block */
add_to_free_list(heap,end);
}
/* This branch is taken if the newly loaded image fits exactly, or
after code GC */
else
{
/* even if there's no room at the end of the heap for a new
free block, we might have to jigger it up by a few bytes in
case prev + prev->size */
if(prev) prev->size = heap->seg->end - (cell)prev;
}
}
static void assert_free_block(free_heap_block *block)
{
if(block->status != B_FREE)
critical_error("Invalid block in free list",(cell)block);
}
static free_heap_block *find_free_block(heap *heap, cell size)
{
cell attempt = size;
while(attempt < free_list_count * block_size_increment)
{
int index = attempt / block_size_increment;
free_heap_block *block = heap->free.small_blocks[index];
if(block)
{
assert_free_block(block);
heap->free.small_blocks[index] = block->next_free;
return block;
}
attempt *= 2;
}
free_heap_block *prev = NULL;
free_heap_block *block = heap->free.large_blocks;
while(block)
{
assert_free_block(block);
if(block->size >= size)
{
if(prev)
prev->next_free = block->next_free;
else
heap->free.large_blocks = block->next_free;
return block;
}
prev = block;
block = block->next_free;
}
return NULL;
}
static free_heap_block *split_free_block(heap *heap, free_heap_block *block, cell size)
{
if(block->size != size )
{
/* split the block in two */
free_heap_block *split = (free_heap_block *)((cell)block + size);
split->status = B_FREE;
split->size = block->size - size;
split->next_free = block->next_free;
block->size = size;
add_to_free_list(heap,split);
}
return block;
}
/* Allocate a block of memory from the mark and sweep GC heap */
heap_block *heap_allot(heap *heap, cell size)
{
size = (size + block_size_increment - 1) & ~(block_size_increment - 1);
free_heap_block *block = find_free_block(heap,size);
if(block)
{
block = split_free_block(heap,block,size);
block->status = B_ALLOCATED;
return block;
}
else
return NULL;
}
/* Deallocates a block manually */
void heap_free(heap *heap, heap_block *block)
{
block->status = B_FREE;
add_to_free_list(heap,(free_heap_block *)block);
}
void mark_block(heap_block *block)
{
/* If already marked, do nothing */
switch(block->status)
{
case B_MARKED:
return;
case B_ALLOCATED:
block->status = B_MARKED;
break;
default:
critical_error("Marking the wrong block",(cell)block);
break;
}
}
/* If in the middle of code GC, we have to grow the heap, data GC restarts from
scratch, so we have to unmark any marked blocks. */
void unmark_marked(heap *heap)
{
heap_block *scan = first_block(heap);
while(scan)
{
if(scan->status == B_MARKED)
scan->status = B_ALLOCATED;
scan = next_block(heap,scan);
}
}
/* After code GC, all referenced code blocks have status set to B_MARKED, so any
which are allocated and not marked can be reclaimed. */
void free_unmarked(heap *heap, heap_iterator iter)
{
clear_free_list(heap);
heap_block *prev = NULL;
heap_block *scan = first_block(heap);
while(scan)
{
switch(scan->status)
{
case B_ALLOCATED:
if(secure_gc)
memset(scan + 1,0,scan->size - sizeof(heap_block));
if(prev && prev->status == B_FREE)
prev->size += scan->size;
else
{
scan->status = B_FREE;
prev = scan;
}
break;
case B_FREE:
if(prev && prev->status == B_FREE)
prev->size += scan->size;
else
prev = scan;
break;
case B_MARKED:
if(prev && prev->status == B_FREE)
add_to_free_list(heap,(free_heap_block *)prev);
scan->status = B_ALLOCATED;
prev = scan;
iter(scan);
break;
default:
critical_error("Invalid scan->status",(cell)scan);
}
scan = next_block(heap,scan);
}
if(prev && prev->status == B_FREE)
add_to_free_list(heap,(free_heap_block *)prev);
}
/* Compute total sum of sizes of free blocks, and size of largest free block */
void heap_usage(heap *heap, cell *used, cell *total_free, cell *max_free)
{
*used = 0;
*total_free = 0;
*max_free = 0;
heap_block *scan = first_block(heap);
while(scan)
{
switch(scan->status)
{
case B_ALLOCATED:
*used += scan->size;
break;
case B_FREE:
*total_free += scan->size;
if(scan->size > *max_free)
*max_free = scan->size;
break;
default:
critical_error("Invalid scan->status",(cell)scan);
}
scan = next_block(heap,scan);
}
}
/* The size of the heap, not including the last block if it's free */
cell heap_size(heap *heap)
{
heap_block *scan = first_block(heap);
while(next_block(heap,scan) != NULL)
scan = next_block(heap,scan);
/* this is the last block in the heap, and it is free */
if(scan->status == B_FREE)
return (cell)scan - heap->seg->start;
/* otherwise the last block is allocated */
else
return heap->seg->size;
}
/* Compute where each block is going to go, after compaction */
cell compute_heap_forwarding(heap *heap, unordered_map<heap_block *,char *> &forwarding)
{
heap_block *scan = first_block(heap);
char *address = (char *)first_block(heap);
while(scan)
{
if(scan->status == B_ALLOCATED)
{
forwarding[scan] = address;
address += scan->size;
}
else if(scan->status == B_MARKED)
critical_error("Why is the block marked?",0);
scan = next_block(heap,scan);
}
return (cell)address - heap->seg->start;
}
void compact_heap(heap *heap, unordered_map<heap_block *,char *> &forwarding)
{
heap_block *scan = first_block(heap);
while(scan)
{
heap_block *next = next_block(heap,scan);
if(scan->status == B_ALLOCATED)
memmove(forwarding[scan],scan,scan->size);
scan = next;
}
}
}