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sortix--sortix/libc/stdlib/heap.cpp
2014-05-16 14:48:27 +02:00

683 lines
16 KiB
C++

/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
stdlib/heap.cpp
Functions that allocate/free memory from a dynamic memory heap.
*******************************************************************************/
#include <sys/mman.h>
#if __STDC_HOSTED__
#include <error.h>
#include <stdio.h>
#include <unistd.h>
#endif
#include <assert.h>
#include <errno.h>
#include <malloc.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#define PARANOIA 1
#if defined(__is_sortix_kernel)
#include <sortix/kernel/decl.h>
#include <sortix/kernel/addralloc.h>
#include <sortix/kernel/kthread.h>
#include <sortix/kernel/log.h>
#include <sortix/kernel/memorymanagement.h>
#include <sortix/kernel/panic.h>
#endif
//
// This first section is just magic compiler/platform stuff, you should
// skip ahead to the actual algorithm.
//
#if defined(__x86_64__)
const size_t MAGIC = 0xDEADDEADDEADDEADUL;
const size_t ALIGNMENT = 16UL;
#else
const size_t MAGIC = 0xDEADDEADUL;
const size_t ALIGNMENT = 8UL;
#endif
const size_t PAGESIZE = 4UL * 1024UL; // 4 KiB
const size_t NUMBINS = 8UL * sizeof(size_t);
static uintptr_t wilderness;
#if defined(__is_sortix_kernel)
static uintptr_t GetHeapStart()
{
return Sortix::GetHeapLower();
}
static void FreeMemory(uintptr_t where, size_t bytes)
{
assert(Sortix::Page::IsAligned(where + bytes));
while ( bytes )
{
addr_t page = Sortix::Memory::Unmap(where);
Sortix::Page::Put(page);
bytes -= PAGESIZE;
where += PAGESIZE;
}
}
static bool AllocateMemory(uintptr_t where, size_t bytes)
{
assert(Sortix::Page::IsAligned(where + bytes));
uintptr_t pos = where;
while ( bytes )
{
addr_t page = Sortix::Page::Get();
if ( !page )
{
FreeMemory(where, pos-where);
return false;
}
if ( !Sortix::Memory::Map(page, pos, PROT_KREAD | PROT_KWRITE) )
{
Sortix::Page::Put(page);
FreeMemory(where, pos-where);
return false;
}
bytes -= PAGESIZE;
pos += PAGESIZE;
}
return true;
}
static bool ExtendHeap(size_t bytesneeded)
{
size_t got_bytes = Sortix::ExpandHeap(bytesneeded);
if ( !got_bytes )
return false;
assert(bytesneeded <= got_bytes);
if ( !AllocateMemory(wilderness, got_bytes) )
{
Sortix::ShrinkHeap(got_bytes);
return false;
}
return true;
}
#else
static uintptr_t GetHeapStart()
{
uintptr_t base = (uintptr_t) sbrk(0);
uintptr_t unaligned = base % ALIGNMENT;
if ( unaligned )
{
sbrk(ALIGNMENT-unaligned);
}
uintptr_t result = (uintptr_t) sbrk(0);
return result;
}
static bool ExtendHeap(size_t bytesneeded)
{
void* newheapend = sbrk(bytesneeded);
return newheapend != (void*) -1UL;
}
#endif
// TODO: BitScanForward and BitScanReverse are x86 instructions, but
// directly using them messes with the optimizer. Once possible, use
// the inline assembly instead of the C-version of the functions.
// Returns the index of the most significant set bit.
inline size_t BSR(size_t Value)
{
#if 1
assert(Value > 0);
for ( size_t I = 8*sizeof(size_t); I > 0; I-- )
{
if ( Value & ( 1UL << (I-1) ) ) { return I-1; }
}
return 0;
#else
size_t Result;
asm("bsr %0, %1" : "=r"(Result) : "r"(Value));
return Result;
#endif
}
// Returns the index of the least significant set bit.
inline size_t BSF(size_t Value)
{
#if 1
assert(Value > 0);
for ( size_t I = 0; I < 8*sizeof(size_t); I++ )
{
if ( Value & ( 1UL << I ) ) { return I; }
}
return 0;
#else
size_t Result;
asm("bsf %0, %1" : "=r"(Result) : "r"(Value));
return Result;
#endif
}
//
// Now for some helper functions and structures.
//
struct Chunk;
struct Trailer;
#if defined(__is_sortix_kernel)
Sortix::kthread_mutex_t heaplock;
#endif
// The location where the heap originally grows from.
uintptr_t heapstart;
// If heap grows down: Location of the first mapped page.
// If heap grows up: Location of the first not-mapped page.
#if 0 /* forward declared abvce */
static uintptr_t wilderness;
#endif
// How many bytes remain in the wilderness.
size_t wildernesssize;
// How many bytes are the heap allow to grow to (including wilderness).
size_t heapmaxsize;
// How many bytes are currently used for chunks in the heap, which
// excludes the wilderness.
size_t heapsize;
// bins[N] contain a linked list of chunks that are at least 2^(N+1)
// bytes, but less than 2^(N+2) bytes. By selecting the proper bin in
// constant time, we can allocate chunks in constant time.
Chunk* bins[NUMBINS];
// Bit N is set if bin[N] contains a chunk.
size_t bincontainschunks;
static bool IsGoodHeapPointer(void* ptr, size_t size)
{
uintptr_t ptrlower = (uintptr_t) ptr;
uintptr_t ptrupper = ptrlower + size;
uintptr_t heaplower = heapstart;
uintptr_t heapupper = wilderness;
return heaplower <= ptrlower && ptrupper <= heapupper;
}
// A preamble to every chunk providing meta-information.
struct Chunk
{
public:
size_t size; // Includes size of Chunk and Trailer
union
{
size_t magic;
Chunk* nextunused;
};
public:
bool IsUsed() { return magic == MAGIC; }
Trailer* GetTrailer();
Chunk* LeftNeighbor();
Chunk* RightNeighbor();
bool IsSane();
};
// A trailer to every chunk providing meta-information.
struct Trailer
{
public:
union
{
size_t magic;
Chunk* prevunused;
};
size_t size; // Includes size of Chunk and Trailer
public:
bool IsUsed() { return magic == MAGIC; }
Chunk* GetChunk();
};
const size_t OVERHEAD = sizeof(Chunk) + sizeof(Trailer);
// This is how a real chunk actually looks:
//struct RealChunk
//{
// Chunk header;
// byte data[...];
// Trailer footer;
// };
Trailer* Chunk::GetTrailer()
{
return (Trailer*) (((uintptr_t) this) + size - sizeof(Trailer));
}
Chunk* Chunk::LeftNeighbor()
{
Trailer* trailer = (Trailer*) (((uintptr_t) this) - sizeof(Trailer));
return trailer->GetChunk();
}
Chunk* Chunk::RightNeighbor()
{
return (Chunk*) (((uintptr_t) this) + size);
}
Chunk* Trailer::GetChunk()
{
return (Chunk*) (((uintptr_t) this) + sizeof(Trailer) - size);
}
bool Chunk::IsSane()
{
if ( !IsGoodHeapPointer(this, sizeof(*this)) )
return false;
if ( !size ) { return false; }
size_t binindex = BSR(size);
Trailer* trailer = GetTrailer();
if ( !IsGoodHeapPointer(trailer, sizeof(*trailer)) )
return false;
if ( trailer->size != size ) { return false; }
if ( IsUsed() )
{
if ( bins[binindex] == this ) { return false; }
if ( magic != MAGIC || trailer->magic != magic ) { return false; }
}
if ( !IsUsed() )
{
if ( ((uintptr_t) nextunused) & (ALIGNMENT-1UL) ) { return false; }
if ( ((uintptr_t) trailer->prevunused) & (ALIGNMENT-1UL) ) { return false; }
if ( nextunused && !IsGoodHeapPointer(nextunused->GetTrailer(),
sizeof(Trailer)) )
return false;
if ( nextunused && nextunused->GetTrailer()->prevunused != this ) { return false; }
if ( trailer->prevunused )
{
if ( !IsGoodHeapPointer(trailer->prevunused,
sizeof(*trailer->prevunused)) )
return false;
if ( bins[binindex] == this ) { return false; }
if ( trailer->prevunused->nextunused != this ) { return false; }
}
if ( !trailer->prevunused )
{
if ( bins[binindex] != this ) { return false; }
if ( !(bincontainschunks & (1UL << binindex)) ) { return false; }
}
}
return true;
}
static void InsertChunk(Chunk* chunk)
{
// Insert the chunk into the right bin.
size_t binindex = BSR(chunk->size);
chunk->GetTrailer()->prevunused = NULL;
chunk->nextunused = bins[binindex];
if ( chunk->nextunused )
{
assert(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = chunk;
}
bins[binindex] = chunk;
bincontainschunks |= (1UL << binindex);
assert(chunk->IsSane());
}
__attribute__((unused))
static bool ValidateHeap()
{
bool foundbin[NUMBINS];
for ( size_t i = 0; i < NUMBINS; i++ ) { foundbin[i] = false; }
Chunk* chunk = (Chunk*) heapstart;
while ( (uintptr_t) chunk < wilderness - wildernesssize )
{
size_t timesfound = 0;
for ( size_t i = 0; i < NUMBINS; i++ )
{
if ( chunk == bins[i] ) { foundbin[i] = true; timesfound++; }
}
if ( 1 < timesfound ) { return false; }
if ( !chunk->IsSane() ) { return false; }
chunk = chunk->RightNeighbor();
}
for ( size_t i = 0; i < NUMBINS; i++ )
{
if ( !bins[i] )
{
if ( foundbin[i] ) { return false; }
continue;
}
if ( !foundbin[i] ) { return false; }
if ( !bins[i]->IsSane() ) { return false; }
}
return true;
}
//
// This is where the actual memory allocation algorithm starts.
//
extern "C" void _init_heap()
{
heapstart = GetHeapStart();
heapmaxsize = SIZE_MAX;
heapsize = 0;
wilderness = heapstart;
wildernesssize = 0;
for ( size_t i = 0; i < NUMBINS; i++ ) { bins[i] = NULL; }
bincontainschunks = 0;
#if defined(__is_sortix_kernel)
heaplock = Sortix::KTHREAD_MUTEX_INITIALIZER;
#endif
}
// Attempts to expand the wilderness such that it contains at least
// bytesneeded bytes. This is done by mapping new pages onto into the
// virtual address-space.
static bool ExpandWilderness(size_t bytesneeded)
{
if ( bytesneeded <= wildernesssize ) { return true; }
bytesneeded -= wildernesssize;
// Align the increase on page boundaries.
const size_t PAGEMASK = ~(PAGESIZE - 1UL);
bytesneeded = ( bytesneeded + PAGESIZE - 1UL ) & PAGEMASK;
assert(bytesneeded >= PAGESIZE);
// TODO: Overflow MAY happen here!
if ( heapmaxsize <= heapsize + wildernesssize + bytesneeded )
return errno = ENOMEM, true;
uintptr_t newwilderness = wilderness + bytesneeded;
// Attempt to map pages so our wilderness grows.
if ( !ExtendHeap(bytesneeded) )
return false;
wildernesssize += bytesneeded;
wilderness = newwilderness;
return true;
}
extern "C" void* malloc(size_t size)
{
#if defined(__is_sortix_kernel)
Sortix::ScopedLock scopedlock(&heaplock);
#endif
#if 2 <= PARANOIA
assert(ValidateHeap());
#endif
// The size field keeps both the allocation and meta information.
size += OVERHEAD;
// Round up to nearest alignment.
size = (size + ALIGNMENT - 1UL) & (~(ALIGNMENT-1UL));
// Find the index of the smallest usable bin.
size_t minbinindex = BSR(size-1UL)+1UL;
// Make a bitmask that filter away all bins that are too small.
size_t minbinmask = ~((1UL << minbinindex) - 1UL);
// Figure out which bins are usable for our chunk.
size_t availablebins = bincontainschunks & minbinmask;
if ( availablebins )
{
// Find the smallest available bin.
size_t binindex = BSF(availablebins);
Chunk* chunk = bins[binindex];
assert(chunk->IsSane());
bins[binindex] = chunk->nextunused;
size_t binsize = 1UL << binindex;
// Mark the bin as empty if we emptied it.
if ( !bins[binindex] )
{
bincontainschunks ^= binsize;
}
else
{
Trailer* trailer = bins[binindex]->GetTrailer();
trailer->prevunused = NULL;
}
assert(!bins[binindex] || bins[binindex]->IsSane());
// If we don't use the entire chunk.
size_t original_chunk_size = chunk->size;
if ( OVERHEAD <= original_chunk_size - size )
{
size_t left = original_chunk_size - size;
chunk->size -= left;
chunk->GetTrailer()->size = chunk->size;
Chunk* leftchunk = chunk->RightNeighbor();
leftchunk->size = left;
Trailer* lefttrailer = leftchunk->GetTrailer();
lefttrailer->size = left;
InsertChunk(leftchunk);
}
chunk->magic = MAGIC;
chunk->GetTrailer()->magic = MAGIC;
#if 3 <= PARANOIA
assert(ValidateHeap());
#endif
uintptr_t result = ((uintptr_t) chunk) + sizeof(Chunk);
return (void*) result;
}
// If no bins are available, try to allocate from the wilderness.
// Check if the wilderness can meet our requirements.
if ( wildernesssize < size && !ExpandWilderness(size) )
{
errno = ENOMEM;
return NULL;
}
// Carve a new chunk out of the wilderness and initialize it.
Chunk* chunk = (Chunk*) (wilderness - wildernesssize);
assert(size <= wildernesssize);
wildernesssize -= size;
heapsize += size;
assert(IsGoodHeapPointer(chunk, sizeof(*chunk)));
chunk->size = size;
Trailer* trailer = chunk->GetTrailer();
assert(IsGoodHeapPointer(trailer, sizeof(*trailer)));
trailer->size = size;
chunk->magic = MAGIC;
trailer->magic = MAGIC;
#if 3 <= PARANOIA
assert(ValidateHeap());
#endif
uintptr_t result = ((uintptr_t) chunk) + sizeof(Chunk);
return (void*) result;
}
static bool IsLeftmostChunk(Chunk* chunk)
{
return heapstart <= (uintptr_t) chunk;
}
static bool IsRightmostChunk(Chunk* chunk)
{
return heapstart + heapsize <= (uintptr_t) chunk + chunk->size;
}
// Removes a chunk from its bin.
static void UnlinkChunk(Chunk* chunk)
{
assert(chunk->IsSane());
Trailer* trailer = chunk->GetTrailer();
if ( trailer->prevunused )
{
assert(trailer->prevunused->IsSane());
trailer->prevunused->nextunused = chunk->nextunused;
if ( chunk->nextunused )
{
assert(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = trailer->prevunused;
}
}
else
{
if ( chunk->nextunused )
{
assert(chunk->nextunused->IsSane());
chunk->nextunused->GetTrailer()->prevunused = NULL;
}
size_t binindex = BSR(chunk->size);
assert(bins[binindex] == chunk);
bins[binindex] = chunk->nextunused;
if ( !bins[binindex] ) { bincontainschunks ^= 1UL << binindex; }
else { assert(bins[binindex]->IsSane()); }
}
}
// Transforms a chunk and its neighbors into a single chunk if possible.
static void UnifyNeighbors(Chunk** chunk)
{
if ( !IsLeftmostChunk(*chunk) )
{
Chunk* neighbor = (*chunk)->LeftNeighbor();
if ( !neighbor->IsUsed() )
{
size_t size = neighbor->size;
size_t chunksize = (*chunk)->size;
UnlinkChunk(neighbor);
*chunk = neighbor;
(*chunk)->size = size + chunksize;
(*chunk)->GetTrailer()->size = (*chunk)->size;
}
}
if ( !IsRightmostChunk(*chunk) )
{
Chunk* neighbor = (*chunk)->RightNeighbor();
if ( !neighbor->IsUsed() )
{
UnlinkChunk(neighbor);
(*chunk)->size += neighbor->size;
(*chunk)->GetTrailer()->size = (*chunk)->size;
}
}
}
extern "C" void free(void* addr)
{
#if defined(__is_sortix_kernel)
Sortix::ScopedLock scopedlock(&heaplock);
#endif
#if 2 <= PARANOIA
assert(ValidateHeap());
#endif
if ( !addr) { return; }
Chunk* chunk = (Chunk*) ((uintptr_t) addr - sizeof(Chunk));
#if __STDC_HOSTED__
if ( !IsGoodHeapPointer(addr, 1) ||
!IsGoodHeapPointer(chunk, sizeof(*chunk)) )
{
error(0, 0, "attempted to free(3) non-heap pointer: 0x%zx", addr);
abort();
}
if ( !chunk->IsUsed() )
{
error(0, 0, "attempted to free(3) area that doesn't appear to be "
"allocated: 0x%zx + 0x%zx", addr);
abort();
}
#endif
assert(chunk->IsUsed());
assert(chunk->IsSane());
UnifyNeighbors(&chunk);
bool nexttowilderness = IsRightmostChunk(chunk);
// If possible, let the wilderness regain the memory.
if ( nexttowilderness )
{
heapsize -= chunk->size;
wildernesssize += chunk->size;
return;
}
InsertChunk(chunk);
#if 3 <= PARANOIA
assert(ValidateHeap());
#endif
}
// TODO: Implement this function properly.
extern "C" void* realloc(void* ptr, size_t size)
{
if ( !ptr ) { return malloc(size); }
Chunk* chunk = (Chunk*) ((uintptr_t) ptr - sizeof(Chunk));
assert(chunk->IsUsed());
assert(chunk->IsSane());
size_t allocsize = chunk->size - OVERHEAD;
if ( size < allocsize ) { return ptr; }
void* newptr = malloc(size);
if ( !newptr ) { return NULL; }
memcpy(newptr, ptr, allocsize);
free(ptr);
return newptr;
}