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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
#include "StackArena.h"
namespace mozilla {
#define STACK_ARENA_MARK_INCREMENT 50
/* a bit under 4096, for malloc overhead */
#define STACK_ARENA_BLOCK_INCREMENT 4044
/**A block of memory that the stack will
* chop up and hand out
*/
struct StackBlock {
// a block of memory. Note that this must be first so that it will
// be aligned.
char mBlock[STACK_ARENA_BLOCK_INCREMENT];
// another block of memory that would only be created
// if our stack overflowed. Yes we have the ability
// to grow on a stack overflow
StackBlock* mNext;
StackBlock() : mNext(nullptr) { }
~StackBlock() { }
};
/* we hold an array of marks. A push pushes a mark on the stack
* a pop pops it off.
*/
struct StackMark {
// the block of memory we are currently handing out chunks of
StackBlock* mBlock;
// our current position in the memory
size_t mPos;
};
StackArena* AutoStackArena::gStackArena;
StackArena::StackArena()
{
mMarkLength = 0;
mMarks = nullptr;
// allocate our stack memory
mBlocks = new StackBlock();
mCurBlock = mBlocks;
mStackTop = 0;
mPos = 0;
}
StackArena::~StackArena()
{
// free up our data
delete[] mMarks;
while(mBlocks)
{
StackBlock* toDelete = mBlocks;
mBlocks = mBlocks->mNext;
delete toDelete;
}
}
size_t
StackArena::SizeOfExcludingThis(nsMallocSizeOfFun aMallocSizeOf) const
{
size_t n = 0;
StackBlock *block = mBlocks;
while (block) {
n += aMallocSizeOf(block);
block = block->mNext;
}
n += aMallocSizeOf(mMarks);
return n;
}
void
StackArena::Push()
{
// Resize the mark array if we overrun it. Failure to allocate the
// mark array is not fatal; we just won't free to that mark. This
// allows callers not to worry about error checking.
if (mStackTop >= mMarkLength)
{
uint32_t newLength = mStackTop + STACK_ARENA_MARK_INCREMENT;
StackMark* newMarks = new StackMark[newLength];
if (newMarks) {
if (mMarkLength)
memcpy(newMarks, mMarks, sizeof(StackMark)*mMarkLength);
// Fill in any marks that we couldn't allocate during a prior call
// to Push().
for (; mMarkLength < mStackTop; ++mMarkLength) {
NS_NOTREACHED("should only hit this on out-of-memory");
newMarks[mMarkLength].mBlock = mCurBlock;
newMarks[mMarkLength].mPos = mPos;
}
delete [] mMarks;
mMarks = newMarks;
mMarkLength = newLength;
}
}
// set a mark at the top (if we can)
NS_ASSERTION(mStackTop < mMarkLength, "out of memory");
if (mStackTop < mMarkLength) {
mMarks[mStackTop].mBlock = mCurBlock;
mMarks[mStackTop].mPos = mPos;
}
mStackTop++;
}
void*
StackArena::Allocate(size_t aSize)
{
NS_ASSERTION(mStackTop > 0, "Allocate called without Push");
// make sure we are aligned. Beard said 8 was safer then 4.
// Round size to multiple of 8
aSize = NS_ROUNDUP<size_t>(aSize, 8);
// if the size makes the stack overflow. Grab another block for the stack
if (mPos + aSize >= STACK_ARENA_BLOCK_INCREMENT)
{
NS_ASSERTION(aSize <= STACK_ARENA_BLOCK_INCREMENT,
"Requested memory is greater that our block size!!");
if (mCurBlock->mNext == nullptr)
mCurBlock->mNext = new StackBlock();
mCurBlock = mCurBlock->mNext;
mPos = 0;
}
// return the chunk they need.
void *result = mCurBlock->mBlock + mPos;
mPos += aSize;
return result;
}
void
StackArena::Pop()
{
// pop off the mark
NS_ASSERTION(mStackTop > 0, "unmatched pop");
mStackTop--;
if (mStackTop >= mMarkLength) {
// We couldn't allocate the marks array at the time of the push, so
// we don't know where we're freeing to.
NS_NOTREACHED("out of memory");
if (mStackTop == 0) {
// But we do know if we've completely pushed the stack.
mCurBlock = mBlocks;
mPos = 0;
}
return;
}
#ifdef DEBUG
// Mark the "freed" memory with 0xdd to help with debugging of memory
// allocation problems.
{
StackBlock *block = mMarks[mStackTop].mBlock, *block_end = mCurBlock;
size_t pos = mMarks[mStackTop].mPos;
for (; block != block_end; block = block->mNext, pos = 0) {
memset(block->mBlock + pos, 0xdd, sizeof(block->mBlock) - pos);
}
memset(block->mBlock + pos, 0xdd, mPos - pos);
}
#endif
mCurBlock = mMarks[mStackTop].mBlock;
mPos = mMarks[mStackTop].mPos;
}
} // namespace mozilla
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