forked from 0ad/0ad
janwas
73683b6109
. the massive renaming undertaking: camelCase functions -> PascalCase. . add some cppdoc. . minor additional renaming improvements: e.g. GetIsClosed -> IsClosed . in entity code, replace constructs like "pvec = new vector; return pvec; use *pvec; delete pvec" with a simple stack variable passed as output parameter (avoid unnecessary dynamic allocs) . timer: simpler handling of raw ticks vs normal timer (less #if) This was SVN commit r5017.
590 lines
11 KiB
C++
590 lines
11 KiB
C++
/**
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* =========================================================================
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* File : lf_alloc.cpp
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* Project : 0 A.D.
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* Description : lock-free memory allocation.
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*
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* @author Jan.Wassenberg@stud.uni-karlsruhe.de
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* =========================================================================
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*/
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/*
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* Copyright (c) 2005 Jan Wassenberg
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*
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* Redistribution and/or modification are also permitted under the
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* terms of the GNU General Public License as published by the
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* Free Software Foundation (version 2 or later, at your option).
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*/
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#include "precompiled.h"
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#if 0
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#include <algorithm>
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#include <limits.h>
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#include "lib.h"
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#include "posix.h"
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#include "lib/sysdep/cpu.h"
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#include "lockfree.h"
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#include "timer.h"
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// superblock descriptor structure
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// one machine word
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struct Anchor
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{
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uint avail : 10;
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uint count : 10;
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uint tag : 10;
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uint state : 2;
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// convert to uintptr_t for CAS
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operator uintptr_t() const
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{
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return *(uintptr_t*)this;
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}
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};
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cassert(sizeof(Anchor) == sizeof(uintptr_t));
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enum State
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{
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ACTIVE = 0,
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FULL = 1,
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PARTIAL = 2,
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EMPTY = 3
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};
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/*typedef void* DescList;
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struct SizeClass
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{
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DescList partial; // initially empty
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size_t sz; // block size
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size_t sb_size; // superblock's size
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};
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struct Descriptor;
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static const uint PTR_BITS = sizeof(void*) * CHAR_BIT;
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struct Active
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{
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uint pdesc : PTR_BITS-6;
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uint credits : 6;
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Active()
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{
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}
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// convert to uintptr_t for CAS
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operator uintptr_t() const
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{
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return *(uintptr_t*)this;
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}
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//
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// allow Active to be used as Descriptor*
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//
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Active& operator=(Descriptor* desc)
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{
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*(Descriptor**)this = desc;
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debug_assert(credits == 0); // make sure ptr is aligned
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return *this;
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}
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Active(Descriptor* desc)
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{
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*this = desc;
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}
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// disambiguate (could otherwise be either uintptr_t or Descriptor*)
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bool operator!() const
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{
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return (uintptr_t)*this != 0;
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}
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operator Descriptor*() const
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{
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return *(Descriptor**)this;
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}
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};
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static const uint MAX_CREDITS = 64; // = 2 ** num_credit_bits
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struct ProcHeap
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{
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Active active; // initially 0; points to Descriptor
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Descriptor* partial; // initially 0
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SizeClass* sc; // parent
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};
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// POD; must be MAX_CREDITS-aligned!
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struct Descriptor
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{
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Anchor anchor;
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Descriptor* next;
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u8* sb; // superblock
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ProcHeap* heap; // -> owner procheap
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size_t sz; // block size
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uint maxcount; // superblock size/sz
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};
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static u8* AllocNewSB(size_t sb_size)
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{
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return 0;
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}
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static void FreeSB(u8* sb)
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{
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}
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static Descriptor* DescAvail = 0;
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static const size_t DESCSBSIZE = 128;
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static Descriptor* DescAlloc()
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{
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Descriptor* desc;
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for(;;)
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{
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desc = DescAvail;
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if(desc)
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{
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Descriptor* next = desc->next;
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if(CAS(&DescAvail, desc, next))
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break;
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}
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else
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{
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desc = (Descriptor*)AllocNewSB(DESCSBSIZE);
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// organize descriptors in a linked list
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cpu_MemoryFence();
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if(CAS(&DescAvail, 0, desc->next))
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break;
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FreeSB((u8*)desc);
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}
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}
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return desc;
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}
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static void DescRetire(Descriptor* desc)
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{
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Descriptor* old_head;
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do
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{
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old_head = DescAvail;
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desc->next = old_head;
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cpu_MemoryFence();
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}
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while(!CAS(&DescAvail, old_head, desc));
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}
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static Descriptor* ListGetPartial(SizeClass* sc)
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{
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return 0;
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}
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static void ListPutPartial(Descriptor* desc)
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{
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}
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static void ListRemoveEmptyDesc(SizeClass* sc)
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{
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}
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static ProcHeap* find_heap(SizeClass* sc)
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{
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return 0;
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}
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static Descriptor* HeapGetPartial(ProcHeap* heap)
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{
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Descriptor* desc;
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do
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{
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desc = heap->partial;
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if(!desc)
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return ListGetPartial(heap->sc);
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}
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while(!CAS(&heap->partial, desc, 0));
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return desc;
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}
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static void HeapPutPartial(Descriptor* desc)
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{
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Descriptor* prev;
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do
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prev = desc->heap->partial;
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while(!CAS(&desc->heap->partial, prev, desc));
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if(prev)
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ListPutPartial(prev);
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}
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static void UpdateActive(ProcHeap* heap, Descriptor* desc, uint more_credits)
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{
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Active new_active = desc;
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new_active.credits = more_credits-1;
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if(CAS(&heap->active, 0, new_active))
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return;
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// someone installed another active sb
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// return credits to sb and make it partial
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Anchor old_anchor, new_anchor;
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do
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{
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new_anchor = old_anchor = desc->anchor;
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new_anchor.count += more_credits;
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new_anchor.state = PARTIAL;
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}
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while(!CAS(&desc->anchor, old_anchor, new_anchor));
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HeapPutPartial(desc);
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}
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static void RemoveEmptyDesc(ProcHeap* heap, Descriptor* desc)
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{
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if(CAS(&heap->partial, desc, 0))
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DescRetire(desc);
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else
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ListRemoveEmptyDesc(heap->sc);
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}
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static void* MallocFromActive(ProcHeap* heap)
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{
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// reserve block
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Active old_active, new_active;
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do
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{
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new_active = old_active = heap->active;
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// no active superblock - will try Partial and then NewSB
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if(!old_active)
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return 0;
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// none left - mark as no longer active
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if(old_active.credits == 0)
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new_active = 0;
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// expected case - reserve
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else
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new_active.credits--;
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}
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while(!CAS(&heap->active, old_active, new_active));
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u8* p;
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// pop block
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Anchor old_anchor, new_anchor;
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Descriptor* desc = old_active;
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uint more_credits;
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do
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{
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new_anchor = old_anchor = desc->anchor;
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p = desc->sb + old_anchor.avail*desc->sz;
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new_anchor.avail = *(uint*)p;
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new_anchor.tag++;
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if(old_active.credits == 0)
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{
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// state must be ACTIVE
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if(old_anchor.count == 0)
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new_anchor.state = FULL;
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else
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{
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more_credits = MIN(old_anchor.count, MAX_CREDITS);
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new_anchor.count -= more_credits;
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}
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}
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}
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while(!CAS(&desc->anchor, old_anchor, new_anchor));
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if(old_active.credits == 0 && old_anchor.count > 0)
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UpdateActive(heap, desc, more_credits);
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*(Descriptor**)p = desc;
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return p+sizeof(void*);
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}
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static void* MallocFromPartial(ProcHeap* heap)
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{
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retry:
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Descriptor* desc = HeapGetPartial(heap);
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if(!desc)
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return 0;
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desc->heap = heap;
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// reserve blocks
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uint more_credits;
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Anchor old_anchor, new_anchor;
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do
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{
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new_anchor = old_anchor = desc->anchor;
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if(old_anchor.state == EMPTY)
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{
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DescRetire(desc);
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goto retry;
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}
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// old_anchor state must be PARTIAL
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// old_anchor count must be > 0
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more_credits = MIN(old_anchor.count-1, MAX_CREDITS);
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new_anchor.count -= more_credits+1;
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new_anchor.state = (more_credits > 0)? ACTIVE : FULL;
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}
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while(!CAS(&desc->anchor, old_anchor, new_anchor));
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u8* p;
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// pop reserved block
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do
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{
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new_anchor = old_anchor = desc->anchor;
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p = desc->sb + old_anchor.avail*desc->sz;
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new_anchor.avail = *(uint*)p;
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new_anchor.tag++;
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}
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while(!CAS(&desc->anchor, old_anchor, new_anchor));
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if(more_credits > 0)
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UpdateActive(heap, desc, more_credits);
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*(Descriptor**)p = desc;
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return p+sizeof(void*);
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}
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static void* MallocFromNewSB(ProcHeap* heap)
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{
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Descriptor* desc = DescAlloc();
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desc->sb = AllocNewSB(heap->sc->sb_size);
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//organize blocks in a linked list starting with index 0
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desc->heap = heap;
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desc->anchor.avail = 1;
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desc->sz = heap->sc->sz;
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desc->maxcount = (uint)(heap->sc->sb_size/desc->sz);
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Active new_active = (Active)desc;
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new_active.credits = MIN(desc->maxcount-1, MAX_CREDITS)-1;
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desc->anchor.count = (desc->maxcount-1)-(new_active.credits+1);
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desc->anchor.state = ACTIVE;
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cpu_MemoryFence();
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if(!CAS(&heap->active, 0, new_active))
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{
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FreeSB(desc->sb);
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return 0;
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}
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u8* p = desc->sb;
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*(Descriptor**)p = desc;
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return p+sizeof(void*);
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}
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void* lf_malloc(size_t sz)
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{
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void* p;
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// use sz and thread id to find heap
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ProcHeap* heap = find_heap(0); // TODO: pass SizeClass
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// large block - allocate directly
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if(!heap)
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{
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p = malloc(sz);
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if(p)
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*(size_t*)p = sz|1;
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return p;
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}
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retry:
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p = MallocFromActive(heap);
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if(p)
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return p;
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p = MallocFromPartial(heap);
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if(p)
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return p;
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p = MallocFromNewSB(heap);
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if(p)
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return p;
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goto retry;
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}
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void lf_free(void* p_)
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{
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if(!p_)
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return;
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u8* p = (u8*)p_;
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// get block header
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p -= sizeof(void*);
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uintptr_t hdr = *(uintptr_t*)p;
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// large block - free directly
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if(hdr & 1)
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{
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free(p);
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return;
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}
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Descriptor* desc = (Descriptor*)hdr;
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u8* sb = desc->sb;
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Anchor old_anchor, new_anchor;
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ProcHeap* heap;
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do
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{
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new_anchor = old_anchor = desc->anchor;
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*(size_t*)p = old_anchor.avail;
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new_anchor.avail = (uint)((p-sb) / desc->sz);
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if(old_anchor.state == FULL)
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new_anchor.state = PARTIAL;
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if(old_anchor.count == desc->maxcount-1)
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{
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heap = desc->heap;
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serialize();
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new_anchor.state = EMPTY;
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}
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else
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new_anchor.count++;
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cpu_MemoryFence();
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}
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while(!CAS(&desc->anchor, old_anchor, new_anchor));
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if(new_anchor.state == EMPTY)
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{
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FreeSB(sb);
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RemoveEmptyDesc(heap, desc);
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}
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else if(old_anchor.state == FULL)
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HeapPutPartial(desc);
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}
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/*
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static const int MAX_POOLS = 8;
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// split out of pools[] for more efficient lookup
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static size_t pool_element_sizes[MAX_POOLS];
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struct Pool
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{
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u8* bucket_pos;
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u8* freelist;
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}
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pools[MAX_POOLS];
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static const int num_pools = 0;
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const size_t BUCKET_SIZE = 8*KiB;
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static u8* bucket_pos;
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// return the pool responsible for <size>, or 0 if not yet set up and
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// there are already too many pools.
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static Pool* responsible_pool(size_t size)
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{
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Pool* pool = pools;
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for(int i = 0; i < MAX_POOLS; i++, pool++)
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if(pool->element_size == size)
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return pool;
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// need to set up a new pool
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// .. but there are too many
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debug_assert(0 <= num_pools && num_pools <= MAX_POOLS);
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if(num_pools >= MAX_POOLS)
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{
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debug_warn("increase MAX_POOLS");
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return 0;
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}
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pool = &pools[num_pools++];
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pool->element_size = size;
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return pool;
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}
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void* sbh_alloc(size_t size)
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{
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// when this allocation is freed, there must be enough room for
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// our freelist pointer. also ensures alignment.
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size = round_up(size, 8);
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// would overflow a bucket
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if(size > BUCKET_SIZE-sizeof(u8*))
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{
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debug_warn("sbh_alloc: size doesn't fit in a bucket");
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return 0;
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}
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//
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//
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}
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TNode* node_alloc(size_t size)
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{
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// would overflow a bucket
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if(size > BUCKET_SIZE-sizeof(u8*))
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{
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debug_warn("node_alloc: size doesn't fit in a bucket");
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return 0;
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}
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size = round_up(size, 8);
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// ensure alignment, since size includes a string
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const uintptr_t addr = (uintptr_t)bucket_pos;
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const size_t bytes_used = addr % BUCKET_SIZE;
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// addr = 0 on first call (no bucket yet allocated)
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// bytes_used == 0 if a node fit exactly into a bucket
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if(addr == 0 || bytes_used == 0 || bytes_used+size > BUCKET_SIZE)
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{
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u8* const prev_bucket = (u8*)addr - bytes_used;
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u8* bucket = (u8*)mem_alloc(BUCKET_SIZE, BUCKET_SIZE);
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if(!bucket)
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return 0;
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*(u8**)bucket = prev_bucket;
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bucket_pos = bucket+round_up(sizeof(u8*), 8);
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}
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TNode* node = (TNode*)bucket_pos;
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bucket_pos = (u8*)node+size;
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return node;
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}
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static void node_free_all()
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{
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const uintptr_t addr = (uintptr_t)bucket_pos;
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u8* bucket = bucket_pos - (addr % BUCKET_SIZE);
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// covers bucket_pos == 0 case
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while(bucket)
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{
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u8* prev_bucket = *(u8**)bucket;
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mem_free(bucket);
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bucket = prev_bucket;
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}
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}
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*/
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#endif
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