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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.
// Garbage collector -- step 0.
//
// Stop the world, mark and sweep garbage collector.
// NOT INTENDED FOR PRODUCTION USE.
//
// A mark and sweep collector provides a way to exercise
// and test the memory allocator and the stack walking machinery
// without also needing to get reference counting
// exactly right.
#include "runtime.h"
#include "malloc.h"
enum {
Debug = 0
};
extern byte data[];
extern byte etext[];
extern byte end[];
enum {
PtrSize = sizeof(void*)
};
static void
scanblock(int32 depth, byte *b, int64 n)
{
int32 off;
void *obj;
uintptr size;
uint32 *ref;
void **vp;
int64 i;
if(Debug)
printf("%d scanblock %p %D\n", depth, b, n);
off = (uint32)(uintptr)b & (PtrSize-1);
if(off) {
b += PtrSize - off;
n -= PtrSize - off;
}
vp = (void**)b;
n /= PtrSize;
for(i=0; i<n; i++) {
if(mlookup(vp[i], &obj, &size, &ref)) {
if(*ref == RefFree || *ref == RefStack)
continue;
if(*ref == RefNone) {
if(Debug)
printf("%d found at %p: ", depth, &vp[i]);
*ref = RefSome;
scanblock(depth+1, obj, size);
}
}
}
}
static void
scanstack(G *gp)
{
Stktop *stk;
byte *sp;
if(gp == g)
sp = (byte*)&gp;
else
sp = gp->sched.sp;
stk = (Stktop*)gp->stackbase;
while(stk) {
scanblock(0, sp, (byte*)stk - sp);
sp = stk->gobuf.sp;
stk = (Stktop*)stk->stackbase;
}
}
static void
mark(void)
{
G *gp;
// mark data+bss
scanblock(0, data, end - data);
// mark stacks
for(gp=allg; gp!=nil; gp=gp->alllink) {
switch(gp->status){
default:
printf("unexpected G.status %d\n", gp->status);
throw("mark - bad status");
case Gdead:
break;
case Grunning:
if(gp != g)
throw("mark - world not stopped");
scanstack(gp);
break;
case Grunnable:
case Gsyscall:
case Gwaiting:
scanstack(gp);
break;
}
}
}
static void
sweepspan(MSpan *s)
{
int32 i, n, npages, size;
byte *p;
if(s->state != MSpanInUse)
return;
p = (byte*)(s->start << PageShift);
if(s->sizeclass == 0) {
// Large block.
switch(s->gcref0) {
default:
throw("bad 'ref count'");
case RefFree:
case RefManual:
case RefStack:
break;
case RefNone:
if(Debug)
printf("free %D at %p\n", (uint64)s->npages<<PageShift, p);
free(p);
break;
case RefSome:
//printf("gc-mem 1 %D\n", (uint64)s->npages<<PageShift);
s->gcref0 = RefNone; // set up for next mark phase
break;
}
return;
}
// Chunk full of small blocks.
// Must match computation in MCentral_Grow.
size = class_to_size[s->sizeclass];
npages = class_to_allocnpages[s->sizeclass];
n = (npages << PageShift) / (size + RefcountOverhead);
for(i=0; i<n; i++) {
switch(s->gcref[i]) {
default:
throw("bad 'ref count'");
case RefFree:
case RefManual:
case RefStack:
break;
case RefNone:
if(Debug)
printf("free %d at %p\n", size, p+i*size);
free(p + i*size);
break;
case RefSome:
s->gcref[i] = RefNone; // set up for next mark phase
break;
}
}
//printf("gc-mem %d %d\n", s->ref, size);
}
static void
sweep(void)
{
MSpan *s;
// Sweep all the spans.
for(s = mheap.allspans; s != nil; s = s->allnext)
sweepspan(s);
}
// Semaphore, not Lock, so that the goroutine
// reschedules when there is contention rather
// than spinning.
static uint32 gcsema = 1;
// Initialized from $GOGC. GOGC=off means no gc.
//
// Next gc is after we've allocated an extra amount of
// memory proportional to the amount already in use.
// If gcpercent=100 and we're using 4M, we'll gc again
// when we get to 8M. This keeps the gc cost in linear
// proportion to the allocation cost. Adjusting gcpercent
// just changes the linear constant (and also the amount of
// extra memory used).
static int32 gcpercent = -2;
void
gc(int32 force)
{
byte *p;
// The gc is turned off (via enablegc) until
// the bootstrap has completed.
// Also, malloc gets called in the guts
// of a number of libraries that might be
// holding locks. To avoid priority inversion
// problems, don't bother trying to run gc
// while holding a lock. The next mallocgc
// without a lock will do the gc instead.
if(!mstats.enablegc || m->locks > 0 || panicking)
return;
if(gcpercent == -2) { // first time through
p = getenv("GOGC");
if(p == nil || p[0] == '\0')
gcpercent = 100;
else if(strcmp(p, (byte*)"off") == 0)
gcpercent = -1;
else
gcpercent = atoi(p);
}
if(gcpercent < 0)
return;
//printf("gc...\n");
semacquire(&gcsema);
m->gcing = 1;
stoptheworld();
if(mheap.Lock.key != 0)
throw("mheap locked during gc");
if(force || mstats.inuse_pages >= mstats.next_gc) {
mark();
sweep();
mstats.next_gc = mstats.inuse_pages+mstats.inuse_pages*gcpercent/100;
}
starttheworld();
m->gcing = 0;
semrelease(&gcsema);
}
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