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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Central free lists.
//
// See malloc.h for an overview.
//
// The MCentral doesn't actually contain the list of free objects; the MSpan does.
// Each MCentral is two lists of MSpans: those with free objects (c->nonempty)
// and those that are completely allocated (c->empty).
//
// TODO(rsc): tcmalloc uses a "transfer cache" to split the list
// into sections of class_to_transfercount[sizeclass] objects
// so that it is faster to move those lists between MCaches and MCentrals.
#include "runtime.h"
#include "malloc.h"
static bool MCentral_Grow(MCentral *c);
static void* MCentral_Alloc(MCentral *c);
static void MCentral_Free(MCentral *c, void *v);
// Initialize a single central free list.
void
runtime_MCentral_Init(MCentral *c, int32 sizeclass)
{
runtime_initlock(c);
c->sizeclass = sizeclass;
runtime_MSpanList_Init(&c->nonempty);
runtime_MSpanList_Init(&c->empty);
}
// Allocate up to n objects from the central free list.
// Return the number of objects allocated.
// The objects are linked together by their first words.
// On return, *pstart points at the first object and *pend at the last.
int32
runtime_MCentral_AllocList(MCentral *c, int32 n, MLink **pfirst)
{
MLink *first, *last, *v;
int32 i;
runtime_lock(c);
// Replenish central list if empty.
if(runtime_MSpanList_IsEmpty(&c->nonempty)) {
if(!MCentral_Grow(c)) {
runtime_unlock(c);
*pfirst = nil;
return 0;
}
}
// Copy from list, up to n.
// First one is guaranteed to work, because we just grew the list.
first = MCentral_Alloc(c);
last = first;
for(i=1; i<n && (v = MCentral_Alloc(c)) != nil; i++) {
last->next = v;
last = v;
}
last->next = nil;
c->nfree -= i;
runtime_unlock(c);
*pfirst = first;
return i;
}
// Helper: allocate one object from the central free list.
static void*
MCentral_Alloc(MCentral *c)
{
MSpan *s;
MLink *v;
if(runtime_MSpanList_IsEmpty(&c->nonempty))
return nil;
s = c->nonempty.next;
s->ref++;
v = s->freelist;
s->freelist = v->next;
if(s->freelist == nil) {
runtime_MSpanList_Remove(s);
runtime_MSpanList_Insert(&c->empty, s);
}
return v;
}
// Free n objects back into the central free list.
// Return the number of objects allocated.
// The objects are linked together by their first words.
// On return, *pstart points at the first object and *pend at the last.
void
runtime_MCentral_FreeList(MCentral *c, int32 n, MLink *start)
{
MLink *v, *next;
// Assume next == nil marks end of list.
// n and end would be useful if we implemented
// the transfer cache optimization in the TODO above.
USED(n);
runtime_lock(c);
for(v=start; v; v=next) {
next = v->next;
MCentral_Free(c, v);
}
runtime_unlock(c);
}
// Helper: free one object back into the central free list.
static void
MCentral_Free(MCentral *c, void *v)
{
MSpan *s;
PageID page;
MLink *p, *next;
int32 size;
// Find span for v.
page = (uintptr)v >> PageShift;
s = runtime_MHeap_Lookup(&runtime_mheap, page);
if(s == nil || s->ref == 0)
runtime_throw("invalid free");
// Move to nonempty if necessary.
if(s->freelist == nil) {
runtime_MSpanList_Remove(s);
runtime_MSpanList_Insert(&c->nonempty, s);
}
// Add v back to s's free list.
p = v;
p->next = s->freelist;
s->freelist = p;
c->nfree++;
// If s is completely freed, return it to the heap.
if(--s->ref == 0) {
size = runtime_class_to_size[c->sizeclass];
runtime_MSpanList_Remove(s);
// The second word of each freed block indicates
// whether it needs to be zeroed. The first word
// is the link pointer and must always be cleared.
for(p=s->freelist; p; p=next) {
next = p->next;
if(size > (int32)sizeof(uintptr) && ((uintptr*)p)[1] != 0)
runtime_memclr((byte*)p, size);
else
p->next = nil;
}
s->freelist = nil;
c->nfree -= (s->npages << PageShift) / size;
runtime_unlock(c);
runtime_MHeap_Free(&runtime_mheap, s, 0);
runtime_lock(c);
}
}
void
runtime_MGetSizeClassInfo(int32 sizeclass, int32 *sizep, int32 *npagesp, int32 *nobj)
{
int32 size;
int32 npages;
npages = runtime_class_to_allocnpages[sizeclass];
size = runtime_class_to_size[sizeclass];
*npagesp = npages;
*sizep = size;
*nobj = (npages << PageShift) / (size + RefcountOverhead);
}
// Fetch a new span from the heap and
// carve into objects for the free list.
static bool
MCentral_Grow(MCentral *c)
{
int32 i, n, npages, size;
MLink **tailp, *v;
byte *p;
MSpan *s;
runtime_unlock(c);
runtime_MGetSizeClassInfo(c->sizeclass, &size, &npages, &n);
s = runtime_MHeap_Alloc(&runtime_mheap, npages, c->sizeclass, 0);
if(s == nil) {
// TODO(rsc): Log out of memory
runtime_lock(c);
return false;
}
// Carve span into sequence of blocks.
tailp = &s->freelist;
p = (byte*)(s->start << PageShift);
s->gcref = (uint32*)(p + size*n);
for(i=0; i<n; i++) {
v = (MLink*)p;
*tailp = v;
tailp = &v->next;
p += size;
}
*tailp = nil;
runtime_lock(c);
c->nfree += n;
runtime_MSpanList_Insert(&c->nonempty, s);
return true;
}
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