mirror of
https://github.com/golang/go
synced 2024-10-03 04:11:21 -06:00
bd4161fcba
introduced explicit "data" symbol instead of etext to mark beginning of data, so that using larger alignment (i.e. 4MB like GNU loader) doesn't confuse garbage collector. split dodata into dodata and dobss in preparation for putting the dynamic data + headers in the data segment instead of stuffed at the beginning of the binary. R=r DELTA=52 (37 added, 3 deleted, 12 changed) OCL=33610 CL=33618
239 lines
4.8 KiB
C
239 lines
4.8 KiB
C
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Garbage collector -- step 0.
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//
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// Stop the world, mark and sweep garbage collector.
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// NOT INTENDED FOR PRODUCTION USE.
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//
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// A mark and sweep collector provides a way to exercise
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// and test the memory allocator and the stack walking machinery
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// without also needing to get reference counting
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// exactly right.
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#include "runtime.h"
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#include "malloc.h"
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enum {
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Debug = 0
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};
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extern byte data[];
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extern byte etext[];
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extern byte end[];
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enum {
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PtrSize = sizeof(void*)
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};
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static void
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scanblock(int32 depth, byte *b, int64 n)
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{
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int32 off;
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void *obj;
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uintptr size;
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uint32 *ref;
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void **vp;
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int64 i;
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if(Debug)
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printf("%d scanblock %p %D\n", depth, b, n);
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off = (uint32)(uintptr)b & (PtrSize-1);
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if(off) {
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b += PtrSize - off;
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n -= PtrSize - off;
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}
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vp = (void**)b;
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n /= PtrSize;
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for(i=0; i<n; i++) {
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if(mlookup(vp[i], &obj, &size, &ref)) {
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if(*ref == RefFree || *ref == RefStack)
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continue;
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if(*ref == RefNone) {
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if(Debug)
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printf("%d found at %p: ", depth, &vp[i]);
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*ref = RefSome;
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scanblock(depth+1, obj, size);
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}
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}
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}
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}
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static void
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scanstack(G *gp)
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{
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Stktop *stk;
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byte *sp;
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if(gp == g)
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sp = (byte*)&gp;
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else
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sp = gp->sched.sp;
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stk = (Stktop*)gp->stackbase;
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while(stk) {
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scanblock(0, sp, (byte*)stk - sp);
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sp = stk->gobuf.sp;
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stk = (Stktop*)stk->stackbase;
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}
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}
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static void
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mark(void)
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{
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G *gp;
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// mark data+bss
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scanblock(0, data, end - data);
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// mark stacks
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for(gp=allg; gp!=nil; gp=gp->alllink) {
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switch(gp->status){
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default:
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printf("unexpected G.status %d\n", gp->status);
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throw("mark - bad status");
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case Gdead:
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break;
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case Grunning:
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if(gp != g)
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throw("mark - world not stopped");
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scanstack(gp);
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break;
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case Grunnable:
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case Gsyscall:
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case Gwaiting:
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scanstack(gp);
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break;
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}
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}
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}
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static void
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sweepspan(MSpan *s)
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{
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int32 i, n, npages, size;
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byte *p;
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if(s->state != MSpanInUse)
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return;
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p = (byte*)(s->start << PageShift);
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if(s->sizeclass == 0) {
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// Large block.
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switch(s->gcref0) {
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default:
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throw("bad 'ref count'");
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case RefFree:
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case RefManual:
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case RefStack:
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break;
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case RefNone:
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if(Debug)
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printf("free %D at %p\n", (uint64)s->npages<<PageShift, p);
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free(p);
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break;
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case RefSome:
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//printf("gc-mem 1 %D\n", (uint64)s->npages<<PageShift);
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s->gcref0 = RefNone; // set up for next mark phase
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break;
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}
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return;
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}
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// Chunk full of small blocks.
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// Must match computation in MCentral_Grow.
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size = class_to_size[s->sizeclass];
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npages = class_to_allocnpages[s->sizeclass];
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n = (npages << PageShift) / (size + RefcountOverhead);
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for(i=0; i<n; i++) {
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switch(s->gcref[i]) {
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default:
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throw("bad 'ref count'");
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case RefFree:
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case RefManual:
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case RefStack:
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break;
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case RefNone:
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if(Debug)
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printf("free %d at %p\n", size, p+i*size);
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free(p + i*size);
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break;
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case RefSome:
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s->gcref[i] = RefNone; // set up for next mark phase
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break;
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}
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}
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//printf("gc-mem %d %d\n", s->ref, size);
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}
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static void
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sweep(void)
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{
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MSpan *s;
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// Sweep all the spans.
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for(s = mheap.allspans; s != nil; s = s->allnext)
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sweepspan(s);
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}
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// Semaphore, not Lock, so that the goroutine
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// reschedules when there is contention rather
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// than spinning.
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static uint32 gcsema = 1;
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// Initialized from $GOGC. GOGC=off means no gc.
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//
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// Next gc is after we've allocated an extra amount of
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// memory proportional to the amount already in use.
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// If gcpercent=100 and we're using 4M, we'll gc again
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// when we get to 8M. This keeps the gc cost in linear
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// proportion to the allocation cost. Adjusting gcpercent
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// just changes the linear constant (and also the amount of
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// extra memory used).
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static int32 gcpercent = -2;
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void
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gc(int32 force)
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{
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byte *p;
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// The gc is turned off (via enablegc) until
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// the bootstrap has completed.
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// Also, malloc gets called in the guts
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// of a number of libraries that might be
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// holding locks. To avoid priority inversion
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// problems, don't bother trying to run gc
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// while holding a lock. The next mallocgc
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// without a lock will do the gc instead.
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if(!mstats.enablegc || m->locks > 0 || panicking)
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return;
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if(gcpercent == -2) { // first time through
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p = getenv("GOGC");
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if(p == nil || p[0] == '\0')
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gcpercent = 100;
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else if(strcmp(p, (byte*)"off") == 0)
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gcpercent = -1;
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else
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gcpercent = atoi(p);
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}
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if(gcpercent < 0)
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return;
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//printf("gc...\n");
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semacquire(&gcsema);
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m->gcing = 1;
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stoptheworld();
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if(mheap.Lock.key != 0)
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throw("mheap locked during gc");
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if(force || mstats.inuse_pages >= mstats.next_gc) {
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mark();
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sweep();
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mstats.next_gc = mstats.inuse_pages+mstats.inuse_pages*gcpercent/100;
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}
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starttheworld();
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m->gcing = 0;
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semrelease(&gcsema);
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}
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