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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
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 #pragma once
#include <AK/Atomic.h>
#include <AK/StdLibExtras.h> #include <AK/StdLibExtras.h>
#include <AK/Types.h> #include <AK/Types.h>
#include <AK/kmalloc.h> #include <AK/kmalloc.h>
@ -55,14 +56,22 @@ public:
{ {
if (!m_head_chunk) if (!m_head_chunk)
return; return;
for_each_chunk([this](auto chunk) { // Note that 'cache_filled' is just an educated guess, and we don't rely on it.
if (!s_unused_allocation_cache) { // If we determine 'cache_filled=true' and the cache becomes empty in the meantime,
auto next_chunk = ((ChunkHeader const*)chunk)->next_chunk; // then we haven't lost much; it was a close call anyway.
if (!next_chunk) { // If we determine 'cache_filled=false' and the cache becomes full in the meantime,
s_unused_allocation_cache = chunk; // 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; return;
} // The cache got filled in the meantime. Oh well, we have to call munmap() anyway.
} }
if constexpr (use_mmap) { if constexpr (use_mmap) {
munmap((void*)chunk, m_chunk_size); munmap((void*)chunk, m_chunk_size);
} else { } 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); // 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; // m_allocations_in_previous_chunk = 0;
void* new_chunk; void* new_chunk = (void*)s_unused_allocation_cache.exchange(0);
if (s_unused_allocation_cache) { if (!new_chunk) {
new_chunk = (void*)exchange(s_unused_allocation_cache, 0);
} else {
if constexpr (use_mmap) { if constexpr (use_mmap) {
#ifdef __serenity__ #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"); 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 }; FlatPtr m_current_chunk { 0 };
size_t m_byte_offset_into_current_chunk { 0 }; size_t m_byte_offset_into_current_chunk { 0 };
size_t m_chunk_size { 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> 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> 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 };
} }