1 files changed, 192 insertions, 0 deletions
diff --git a/src/pkg/runtime/mcentral.c b/src/pkg/runtime/mcentral.c
new file mode 100644
index 000000000..5c9f720c0
--- /dev/null
+++ b/src/pkg/runtime/mcentral.c
@@ -0,0 +1,192 @@
+// 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
+MCentral_Init(MCentral *c, int32 sizeclass)
+{
+	c->sizeclass = sizeclass;
+	MSpanList_Init(&c->nonempty);
+	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
+MCentral_AllocList(MCentral *c, int32 n, MLink **pfirst)
+{
+	MLink *first, *last, *v;
+	int32 i;
+
+
+	lock(c);
+	// Replenish central list if empty.
+	if(MSpanList_IsEmpty(&c->nonempty)) {
+		if(!MCentral_Grow(c)) {
+			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;
+
+	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(MSpanList_IsEmpty(&c->nonempty))
+		return nil;
+	s = c->nonempty.next;
+	s->ref++;
+	v = s->freelist;
+	s->freelist = v->next;
+	if(s->freelist == nil) {
+		MSpanList_Remove(s);
+		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
+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);
+
+	lock(c);
+	for(v=start; v; v=next) {
+		next = v->next;
+		MCentral_Free(c, v);
+	}
+	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;
+
+	// Find span for v.
+	page = (uintptr)v >> PageShift;
+	s = MHeap_Lookup(&mheap, page);
+	if(s == nil || s->ref == 0)
+		throw("invalid free");
+
+	// Move to nonempty if necessary.
+	if(s->freelist == nil) {
+		MSpanList_Remove(s);
+		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) {
+		MSpanList_Remove(s);
+		// Freed blocks are zeroed except for the link pointer.
+		// Zero the link pointers so that the page is all zero.
+		for(p=s->freelist; p; p=next) {
+			next = p->next;
+			p->next = nil;
+		}
+		s->freelist = nil;
+		c->nfree -= (s->npages << PageShift) / class_to_size[c->sizeclass];
+		unlock(c);
+		MHeap_Free(&mheap, s);
+		lock(c);
+	}
+}
+
+// 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;
+
+	unlock(c);
+	npages = class_to_allocnpages[c->sizeclass];
+	s = MHeap_Alloc(&mheap, npages, c->sizeclass);
+	if(s == nil) {
+		// TODO(rsc): Log out of memory
+		lock(c);
+		return false;
+	}
+
+	// Carve span into sequence of blocks.
+	tailp = &s->freelist;
+	p = (byte*)(s->start << PageShift);
+	size = class_to_size[c->sizeclass];
+	n = (npages << PageShift) / (size + RefcountOverhead);
+	s->gcref = (uint32*)(p + size*n);
+	for(i=0; i<n; i++) {
+		v = (MLink*)p;
+		*tailp = v;
+		tailp = &v->next;
+		p += size;
+	}
+	*tailp = nil;
+
+	lock(c);
+	c->nfree += n;
+	MSpanList_Insert(&c->nonempty, s);
+	return true;
+}