// 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;
}
static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
uintptr n;
MSpan *s, *t;
PageID p;
// To prevent excessive heap growth, before allocating n pages
// we need to sweep and reclaim at least n pages.
if(!h->sweepdone)
MHeap_Reclaim(h, npage);
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
s = h->free[n].next;
goto HaveSpan;
}
}
// Best fit in list of large spans.
if((s = MHeap_AllocLarge(h, npage)) == nil) {
if(!MHeap_Grow(h, npage))
return nil;
if((s = MHeap_AllocLarge(h, npage)) == nil)
return nil;
}
HaveSpan:
// Mark span in use.
if(s->state != MSpanFree)
runtime_throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime_throw("MHeap_AllocLocked - bad npages");
runtime_MSpanList_Remove(s);
runtime_atomicstore(&s->sweepgen, h->sweepgen);
s->state = MSpanInUse;
mstats.heap_idle -= s->npages<<PageShift;
mstats.heap_released -= s->npreleased<<PageShift;
if(s->npreleased > 0)
runtime_SysUsed((void*)(s->start<<PageShift), s->npages<<PageShift);
s->npreleased = 0;
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime_FixAlloc_Alloc(&h->spanalloc);
runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->spans[p-1] = s;
h->spans[p] = t;
h->spans[p+t->npages-1] = t;
t->needzero = s->needzero;
runtime_atomicstore(&t->sweepgen, h->sweepgen);
t->state = MSpanInUse;
MHeap_FreeLocked(h, t);
t->unusedsince = s->unusedsince; // preserve age
}
static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
uintptr n;
MSpan *s, *t;
PageID p;
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
s = h->free[n].next;
goto HaveSpan;
}
}
// Best fit in list of large spans.
if((s = MHeap_AllocLarge(h, npage)) == nil) {
if(!MHeap_Grow(h, npage))
return nil;
if((s = MHeap_AllocLarge(h, npage)) == nil)
return nil;
}
HaveSpan:
// Mark span in use.
if(s->state != MSpanFree)
runtime_throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime_throw("MHeap_AllocLocked - bad npages");
runtime_MSpanList_Remove(s);
s->state = MSpanInUse;
mstats.heap_idle -= s->npages<<PageShift;
mstats.heap_released -= s->npreleased<<PageShift;
s->npreleased = 0;
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime_FixAlloc_Alloc(&h->spanalloc);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
if(sizeof(void*) == 8)
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->map[p-1] = s;
h->map[p] = t;
h->map[p+t->npages-1] = t;
*(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift); // copy "needs zeroing" mark
t->state = MSpanInUse;
MHeap_FreeLocked(h, t);
}
// 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;
}
static MSpan*
MHeap_AllocLocked(MHeap *h, uintptr npage, int32 sizeclass)
{
uintptr n;
MSpan *s, *t;
PageID p;
// Try in fixed-size lists up to max.
for(n=npage; n < nelem(h->free); n++) {
if(!runtime_MSpanList_IsEmpty(&h->free[n])) {
s = h->free[n].next;
goto HaveSpan;
}
}
// Best fit in list of large spans.
if((s = MHeap_AllocLarge(h, npage)) == nil) {
if(!MHeap_Grow(h, npage))
return nil;
if((s = MHeap_AllocLarge(h, npage)) == nil)
return nil;
}
HaveSpan:
// Mark span in use.
if(s->state != MSpanFree)
runtime_throw("MHeap_AllocLocked - MSpan not free");
if(s->npages < npage)
runtime_throw("MHeap_AllocLocked - bad npages");
runtime_MSpanList_Remove(s);
s->state = MSpanInUse;
mstats.heap_idle -= s->npages<<PageShift;
mstats.heap_released -= s->npreleased<<PageShift;
if(s->npreleased > 0) {
// We have called runtime_SysUnused with these pages, and on
// Unix systems it called madvise. At this point at least
// some BSD-based kernels will return these pages either as
// zeros or with the old data. For our caller, the first word
// in the page indicates whether the span contains zeros or
// not (this word was set when the span was freed by
// MCentral_Free or runtime_MCentral_FreeSpan). If the first
// page in the span is returned as zeros, and some subsequent
// page is returned with the old data, then we will be
// returning a span that is assumed to be all zeros, but the
// actual data will not be all zeros. Avoid that problem by
// explicitly marking the span as not being zeroed, just in
// case. The beadbead constant we use here means nothing, it
// is just a unique constant not seen elsewhere in the
// runtime, as a clue in case it turns up unexpectedly in
// memory or in a stack trace.
*(uintptr*)(s->start<<PageShift) = (uintptr)0xbeadbeadbeadbeadULL;
}
s->npreleased = 0;
if(s->npages > npage) {
// Trim extra and put it back in the heap.
t = runtime_FixAlloc_Alloc(&h->spanalloc);
mstats.mspan_inuse = h->spanalloc.inuse;
mstats.mspan_sys = h->spanalloc.sys;
runtime_MSpan_Init(t, s->start + npage, s->npages - npage);
s->npages = npage;
p = t->start;
p -= ((uintptr)h->arena_start>>PageShift);
if(p > 0)
h->map[p-1] = s;
h->map[p] = t;
h->map[p+t->npages-1] = t;
*(uintptr*)(t->start<<PageShift) = *(uintptr*)(s->start<<PageShift); // copy "needs zeroing" mark
t->state = MSpanInUse;
MHeap_FreeLocked(h, t);
t->unusedsince = s->unusedsince; // preserve age
}