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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.
// Per-thread (in Go, per-M) malloc cache for small objects.
//
// See malloc.h for an overview.
#include "runtime.h"
#include "malloc.h"
void*
runtime_MCache_Alloc(MCache *c, int32 sizeclass, uintptr size, int32 zeroed)
{
MCacheList *l;
MLink *first, *v;
int32 n;
// Allocate from list.
l = &c->list[sizeclass];
if(l->list == nil) {
// Replenish using central lists.
n = runtime_MCentral_AllocList(&runtime_mheap.central[sizeclass],
runtime_class_to_transfercount[sizeclass], &first);
l->list = first;
l->nlist = n;
c->size += n*size;
}
v = l->list;
l->list = v->next;
l->nlist--;
if(l->nlist < l->nlistmin)
l->nlistmin = l->nlist;
c->size -= size;
// v is zeroed except for the link pointer
// that we used above; zero that.
v->next = nil;
if(zeroed) {
// block is zeroed iff second word is zero ...
if(size > sizeof(uintptr) && ((uintptr*)v)[1] != 0)
runtime_memclr((byte*)v, size);
else {
// ... except for the link pointer
// that we used above; zero that.
v->next = nil;
}
}
c->local_alloc += size;
c->local_objects++;
return v;
}
// Take n elements off l and return them to the central free list.
static void
ReleaseN(MCache *c, MCacheList *l, int32 n, int32 sizeclass)
{
MLink *first, **lp;
int32 i;
// Cut off first n elements.
first = l->list;
lp = &l->list;
for(i=0; i<n; i++)
lp = &(*lp)->next;
l->list = *lp;
*lp = nil;
l->nlist -= n;
if(l->nlist < l->nlistmin)
l->nlistmin = l->nlist;
c->size -= n*runtime_class_to_size[sizeclass];
// Return them to central free list.
runtime_MCentral_FreeList(&runtime_mheap.central[sizeclass], n, first);
}
void
runtime_MCache_Free(MCache *c, void *v, int32 sizeclass, uintptr size)
{
int32 i, n;
MCacheList *l;
MLink *p;
// Put back on list.
l = &c->list[sizeclass];
p = v;
p->next = l->list;
l->list = p;
l->nlist++;
c->size += size;
c->local_alloc -= size;
c->local_objects--;
if(l->nlist >= MaxMCacheListLen) {
// Release a chunk back.
ReleaseN(c, l, runtime_class_to_transfercount[sizeclass], sizeclass);
}
if(c->size >= MaxMCacheSize) {
// Scavenge.
for(i=0; i<NumSizeClasses; i++) {
l = &c->list[i];
n = l->nlistmin;
// n is the minimum number of elements we've seen on
// the list since the last scavenge. If n > 0, it means that
// we could have gotten by with n fewer elements
// without needing to consult the central free list.
// Move toward that situation by releasing n/2 of them.
if(n > 0) {
if(n > 1)
n /= 2;
ReleaseN(c, l, n, i);
}
l->nlistmin = l->nlist;
}
}
}
void
runtime_MCache_ReleaseAll(MCache *c)
{
int32 i;
MCacheList *l;
for(i=0; i<NumSizeClasses; i++) {
l = &c->list[i];
ReleaseN(c, l, l->nlist, i);
l->nlistmin = 0;
}
}
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