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AK: Make BumpAllocator work in multi-threaded environments

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Fixes #10578.
This commit is contained in:
Ben Wiederhake 2021-10-29 00:49:11 +02:00 committed by Linus Groh
parent 2c901ae2be
commit 03526a7f2b
Notes: sideshowbarker 2024-07-18 01:40:15 +09:00 
Author: https://github.com/BenWiederhake
Commit: https://github.com/SerenityOS/serenity/commit/03526a7f2b3
Pull-request: https://github.com/SerenityOS/serenity/pull/10676
Issue: https://github.com/SerenityOS/serenity/issues/10578
Reviewed-by: https://github.com/alimpfard
1 changed files with 19 additions and 12 deletions
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31
AK/BumpAllocator.h
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@ -6,6 +6,7 @@
#pragma once
#include <AK/Atomic.h>
#include <AK/StdLibExtras.h>
#include <AK/Types.h>
#include <AK/kmalloc.h>
@ -55,14 +56,22 @@ public:
{
if (!m_head_chunk)
return;
for_each_chunk([this](auto chunk) {
if (!s_unused_allocation_cache) {
auto next_chunk = ((ChunkHeader const*)chunk)->next_chunk;
if (!next_chunk) {
s_unused_allocation_cache = chunk;
// Note that 'cache_filled' is just an educated guess, and we don't rely on it.
// If we determine 'cache_filled=true' and the cache becomes empty in the meantime,
// then we haven't lost much; it was a close call anyway.
// If we determine 'cache_filled=false' and the cache becomes full in the meantime,
// then we'll end up with a different chunk to munmap(), no big difference.
bool cache_filled = s_unused_allocation_cache.load(MemoryOrder::memory_order_relaxed);
for_each_chunk([&](auto chunk) {
if (!cache_filled) {
cache_filled = true;
((ChunkHeader*)chunk)->next_chunk = 0;
chunk = s_unused_allocation_cache.exchange(chunk);
if (!chunk)
return;
}
// The cache got filled in the meantime. Oh well, we have to call munmap() anyway.
}
if constexpr (use_mmap) {
munmap((void*)chunk, m_chunk_size);
} else {
@ -91,10 +100,8 @@ protected:
{
// dbgln("Allocated {} entries in previous chunk and have {} unusable bytes", m_allocations_in_previous_chunk, m_chunk_size - m_byte_offset_into_current_chunk);
// m_allocations_in_previous_chunk = 0;
void* new_chunk;
if (s_unused_allocation_cache) {
new_chunk = (void*)exchange(s_unused_allocation_cache, 0);
} else {
void* new_chunk = (void*)s_unused_allocation_cache.exchange(0);
if (!new_chunk) {
if constexpr (use_mmap) {
#ifdef __serenity__
new_chunk = serenity_mmap(nullptr, m_chunk_size, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_RANDOMIZED | MAP_PRIVATE, 0, 0, m_chunk_size, "BumpAllocator Chunk");
@ -140,7 +147,7 @@ protected:
FlatPtr m_current_chunk { 0 };
size_t m_byte_offset_into_current_chunk { 0 };
size_t m_chunk_size { 0 };
static FlatPtr s_unused_allocation_cache;
static Atomic<FlatPtr> s_unused_allocation_cache;
};
template<typename T, bool use_mmap = false, size_t chunk_size = use_mmap ? 4 * MiB : 4 * KiB>
@ -186,7 +193,7 @@ public:
};
template<bool use_mmap, size_t size>
inline FlatPtr BumpAllocator<use_mmap, size>::s_unused_allocation_cache { 0 };
inline Atomic<FlatPtr> BumpAllocator<use_mmap, size>::s_unused_allocation_cache { 0 };
}