diff options
Diffstat (limited to 'src/runtime/mgc.go')
| -rw-r--r-- | src/runtime/mgc.go | 1798 |
1 files changed, 1798 insertions, 0 deletions
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go new file mode 100644 index 000000000..f44d7ddbc --- /dev/null +++ b/src/runtime/mgc.go @@ -0,0 +1,1798 @@ +// 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. + +// TODO(rsc): The code having to do with the heap bitmap needs very serious cleanup. +// It has gotten completely out of control. + +// Garbage collector (GC). +// +// GC is: +// - mark&sweep +// - mostly precise (with the exception of some C-allocated objects, assembly frames/arguments, etc) +// - parallel (up to MaxGcproc threads) +// - partially concurrent (mark is stop-the-world, while sweep is concurrent) +// - non-moving/non-compacting +// - full (non-partial) +// +// GC rate. +// Next GC is after we've allocated an extra amount of memory proportional to +// the amount already in use. The proportion is controlled by GOGC environment variable +// (100 by default). If GOGC=100 and we're using 4M, we'll GC again when we get to 8M +// (this mark is tracked in next_gc variable). This keeps the GC cost in linear +// proportion to the allocation cost. Adjusting GOGC just changes the linear constant +// (and also the amount of extra memory used). +// +// Concurrent sweep. +// The sweep phase proceeds concurrently with normal program execution. +// The heap is swept span-by-span both lazily (when a goroutine needs another span) +// and concurrently in a background goroutine (this helps programs that are not CPU bound). +// However, at the end of the stop-the-world GC phase we don't know the size of the live heap, +// and so next_gc calculation is tricky and happens as follows. +// At the end of the stop-the-world phase next_gc is conservatively set based on total +// heap size; all spans are marked as "needs sweeping". +// Whenever a span is swept, next_gc is decremented by GOGC*newly_freed_memory. +// The background sweeper goroutine simply sweeps spans one-by-one bringing next_gc +// closer to the target value. However, this is not enough to avoid over-allocating memory. +// Consider that a goroutine wants to allocate a new span for a large object and +// there are no free swept spans, but there are small-object unswept spans. +// If the goroutine naively allocates a new span, it can surpass the yet-unknown +// target next_gc value. In order to prevent such cases (1) when a goroutine needs +// to allocate a new small-object span, it sweeps small-object spans for the same +// object size until it frees at least one object; (2) when a goroutine needs to +// allocate large-object span from heap, it sweeps spans until it frees at least +// that many pages into heap. Together these two measures ensure that we don't surpass +// target next_gc value by a large margin. There is an exception: if a goroutine sweeps +// and frees two nonadjacent one-page spans to the heap, it will allocate a new two-page span, +// but there can still be other one-page unswept spans which could be combined into a two-page span. +// It's critical to ensure that no operations proceed on unswept spans (that would corrupt +// mark bits in GC bitmap). During GC all mcaches are flushed into the central cache, +// so they are empty. When a goroutine grabs a new span into mcache, it sweeps it. +// When a goroutine explicitly frees an object or sets a finalizer, it ensures that +// the span is swept (either by sweeping it, or by waiting for the concurrent sweep to finish). +// The finalizer goroutine is kicked off only when all spans are swept. +// When the next GC starts, it sweeps all not-yet-swept spans (if any). + +package runtime + +import "unsafe" + +const ( + _DebugGC = 0 + _DebugGCPtrs = false // if true, print trace of every pointer load during GC + _ConcurrentSweep = true + + _WorkbufSize = 4 * 1024 + _FinBlockSize = 4 * 1024 + _RootData = 0 + _RootBss = 1 + _RootFinalizers = 2 + _RootSpans = 3 + _RootFlushCaches = 4 + _RootCount = 5 +) + +// ptrmask for an allocation containing a single pointer. +var oneptr = [...]uint8{bitsPointer} + +// Initialized from $GOGC. GOGC=off means no gc. +var gcpercent int32 + +// Holding worldsema grants an M the right to try to stop the world. +// The procedure is: +// +// semacquire(&worldsema); +// m.gcing = 1; +// stoptheworld(); +// +// ... do stuff ... +// +// m.gcing = 0; +// semrelease(&worldsema); +// starttheworld(); +// +var worldsema uint32 = 1 + +type workbuf struct { + node lfnode // must be first + nobj uintptr + obj [(_WorkbufSize - unsafe.Sizeof(lfnode{}) - ptrSize) / ptrSize]uintptr +} + +var data, edata, bss, ebss, gcdata, gcbss struct{} + +var finlock mutex // protects the following variables +var fing *g // goroutine that runs finalizers +var finq *finblock // list of finalizers that are to be executed +var finc *finblock // cache of free blocks +var finptrmask [_FinBlockSize / ptrSize / pointersPerByte]byte +var fingwait bool +var fingwake bool +var allfin *finblock // list of all blocks + +var gcdatamask bitvector +var gcbssmask bitvector + +var gclock mutex + +var badblock [1024]uintptr +var nbadblock int32 + +type workdata struct { + full uint64 // lock-free list of full blocks + empty uint64 // lock-free list of empty blocks + pad0 [_CacheLineSize]uint8 // prevents false-sharing between full/empty and nproc/nwait + nproc uint32 + tstart int64 + nwait uint32 + ndone uint32 + alldone note + markfor *parfor + + // Copy of mheap.allspans for marker or sweeper. + spans []*mspan +} + +var work workdata + +//go:linkname weak_cgo_allocate go.weak.runtime._cgo_allocate_internal +var weak_cgo_allocate byte + +// Is _cgo_allocate linked into the binary? +func have_cgo_allocate() bool { + return &weak_cgo_allocate != nil +} + +// scanblock scans a block of n bytes starting at pointer b for references +// to other objects, scanning any it finds recursively until there are no +// unscanned objects left. Instead of using an explicit recursion, it keeps +// a work list in the Workbuf* structures and loops in the main function +// body. Keeping an explicit work list is easier on the stack allocator and +// more efficient. +func scanblock(b, n uintptr, ptrmask *uint8) { + // Cache memory arena parameters in local vars. + arena_start := mheap_.arena_start + arena_used := mheap_.arena_used + + wbuf := getempty(nil) + nobj := wbuf.nobj + wp := &wbuf.obj[nobj] + keepworking := b == 0 + + var ptrbitp unsafe.Pointer + + // ptrmask can have 2 possible values: + // 1. nil - obtain pointer mask from GC bitmap. + // 2. pointer to a compact mask (for stacks and data). + goto_scanobj := b != 0 + + for { + if goto_scanobj { + goto_scanobj = false + } else { + if nobj == 0 { + // Out of work in workbuf. + if !keepworking { + putempty(wbuf) + return + } + + // Refill workbuf from global queue. + wbuf = getfull(wbuf) + if wbuf == nil { + return + } + nobj = wbuf.nobj + if nobj < uintptr(len(wbuf.obj)) { + wp = &wbuf.obj[nobj] + } else { + wp = nil + } + } + + // If another proc wants a pointer, give it some. + if work.nwait > 0 && nobj > 4 && work.full == 0 { + wbuf.nobj = nobj + wbuf = handoff(wbuf) + nobj = wbuf.nobj + if nobj < uintptr(len(wbuf.obj)) { + wp = &wbuf.obj[nobj] + } else { + wp = nil + } + } + + nobj-- + wp = &wbuf.obj[nobj] + b = *wp + n = arena_used - uintptr(b) + ptrmask = nil // use GC bitmap for pointer info + } + + if _DebugGCPtrs { + print("scanblock ", b, " +", hex(n), " ", ptrmask, "\n") + } + + // Find bits of the beginning of the object. + if ptrmask == nil { + off := (uintptr(b) - arena_start) / ptrSize + ptrbitp = unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1) + } + + var i uintptr + for i = 0; i < n; i += ptrSize { + // Find bits for this word. + var bits uintptr + if ptrmask == nil { + // Check if we have reached end of span. + if (uintptr(b)+i)%_PageSize == 0 && + h_spans[(uintptr(b)-arena_start)>>_PageShift] != h_spans[(uintptr(b)+i-arena_start)>>_PageShift] { + break + } + + // Consult GC bitmap. + bits = uintptr(*(*byte)(ptrbitp)) + + if wordsPerBitmapByte != 2 { + gothrow("alg doesn't work for wordsPerBitmapByte != 2") + } + j := (uintptr(b) + i) / ptrSize & 1 + ptrbitp = add(ptrbitp, -j) + bits >>= gcBits * j + + if bits&bitBoundary != 0 && i != 0 { + break // reached beginning of the next object + } + bits = (bits >> 2) & bitsMask + if bits == bitsDead { + break // reached no-scan part of the object + } + } else { + // dense mask (stack or data) + bits = (uintptr(*(*byte)(add(unsafe.Pointer(ptrmask), (i/ptrSize)/4))) >> (((i / ptrSize) % 4) * bitsPerPointer)) & bitsMask + } + + if bits <= _BitsScalar { // BitsScalar || BitsDead + continue + } + + if bits != _BitsPointer { + gothrow("unexpected garbage collection bits") + } + + obj := *(*uintptr)(unsafe.Pointer(b + i)) + obj0 := obj + + markobj: + var s *mspan + var off, bitp, shift, xbits uintptr + + // At this point we have extracted the next potential pointer. + // Check if it points into heap. + if obj == 0 { + continue + } + if obj < arena_start || arena_used <= obj { + if uintptr(obj) < _PhysPageSize && invalidptr != 0 { + s = nil + goto badobj + } + continue + } + + // Mark the object. + obj &^= ptrSize - 1 + off = (obj - arena_start) / ptrSize + bitp = arena_start - off/wordsPerBitmapByte - 1 + shift = (off % wordsPerBitmapByte) * gcBits + xbits = uintptr(*(*byte)(unsafe.Pointer(bitp))) + bits = (xbits >> shift) & bitMask + if (bits & bitBoundary) == 0 { + // Not a beginning of a block, consult span table to find the block beginning. + k := pageID(obj >> _PageShift) + x := k + x -= pageID(arena_start >> _PageShift) + s = h_spans[x] + if s == nil || k < s.start || s.limit <= obj || s.state != mSpanInUse { + // Stack pointers lie within the arena bounds but are not part of the GC heap. + // Ignore them. + if s != nil && s.state == _MSpanStack { + continue + } + goto badobj + } + p := uintptr(s.start) << _PageShift + if s.sizeclass != 0 { + size := s.elemsize + idx := (obj - p) / size + p = p + idx*size + } + if p == obj { + print("runtime: failed to find block beginning for ", hex(p), " s=", hex(s.start*_PageSize), " s.limit=", hex(s.limit), "\n") + gothrow("failed to find block beginning") + } + obj = p + goto markobj + } + + if _DebugGCPtrs { + print("scan *", hex(b+i), " = ", hex(obj0), " => base ", hex(obj), "\n") + } + + if nbadblock > 0 && obj == badblock[nbadblock-1] { + // Running garbage collection again because + // we want to find the path from a root to a bad pointer. + // Found possible next step; extend or finish path. + for j := int32(0); j < nbadblock; j++ { + if badblock[j] == b { + goto AlreadyBad + } + } + print("runtime: found *(", hex(b), "+", hex(i), ") = ", hex(obj0), "+", hex(obj-obj0), "\n") + if ptrmask != nil { + gothrow("bad pointer") + } + if nbadblock >= int32(len(badblock)) { + gothrow("badblock trace too long") + } + badblock[nbadblock] = uintptr(b) + nbadblock++ + AlreadyBad: + } + + // Now we have bits, bitp, and shift correct for + // obj pointing at the base of the object. + // Only care about not marked objects. + if bits&bitMarked != 0 { + continue + } + + // If obj size is greater than 8, then each byte of GC bitmap + // contains info for at most one object. In such case we use + // non-atomic byte store to mark the object. This can lead + // to double enqueue of the object for scanning, but scanning + // is an idempotent operation, so it is OK. This cannot lead + // to bitmap corruption because the single marked bit is the + // only thing that can change in the byte. + // For 8-byte objects we use non-atomic store, if the other + // quadruple is already marked. Otherwise we resort to CAS + // loop for marking. + if xbits&(bitMask|bitMask<<gcBits) != bitBoundary|bitBoundary<<gcBits || work.nproc == 1 { + *(*byte)(unsafe.Pointer(bitp)) = uint8(xbits | bitMarked<<shift) + } else { + atomicor8((*byte)(unsafe.Pointer(bitp)), bitMarked<<shift) + } + + if (xbits>>(shift+2))&bitsMask == bitsDead { + continue // noscan object + } + + // Queue the obj for scanning. + // TODO: PREFETCH here. + + // If workbuf is full, obtain an empty one. + if nobj >= uintptr(len(wbuf.obj)) { + wbuf.nobj = nobj + wbuf = getempty(wbuf) + nobj = wbuf.nobj + wp = &wbuf.obj[nobj] + } + *wp = obj + nobj++ + if nobj < uintptr(len(wbuf.obj)) { + wp = &wbuf.obj[nobj] + } else { + wp = nil + } + continue + + badobj: + // If cgo_allocate is linked into the binary, it can allocate + // memory as []unsafe.Pointer that may not contain actual + // pointers and must be scanned conservatively. + // In this case alone, allow the bad pointer. + if have_cgo_allocate() && ptrmask == nil { + continue + } + + // Anything else indicates a bug somewhere. + // If we're in the middle of chasing down a different bad pointer, + // don't confuse the trace by printing about this one. + if nbadblock > 0 { + continue + } + + print("runtime: garbage collector found invalid heap pointer *(", hex(b), "+", hex(i), ")=", hex(obj)) + if s == nil { + print(" s=nil\n") + } else { + print(" span=", uintptr(s.start)<<_PageShift, "-", s.limit, "-", (uintptr(s.start)+s.npages)<<_PageShift, " state=", s.state, "\n") + } + if ptrmask != nil { + gothrow("invalid heap pointer") + } + // Add to badblock list, which will cause the garbage collection + // to keep repeating until it has traced the chain of pointers + // leading to obj all the way back to a root. + if nbadblock == 0 { + badblock[nbadblock] = uintptr(b) + nbadblock++ + } + } + if _DebugGCPtrs { + print("end scanblock ", hex(b), " +", hex(n), " ", ptrmask, "\n") + } + if _DebugGC > 0 && ptrmask == nil { + // For heap objects ensure that we did not overscan. + var p, n uintptr + if mlookup(b, &p, &n, nil) == 0 || b != p || i > n { + print("runtime: scanned (", hex(b), "+", hex(i), "), heap object (", hex(p), "+", hex(n), ")\n") + gothrow("scanblock: scanned invalid object") + } + } + } +} + +func markroot(desc *parfor, i uint32) { + // Note: if you add a case here, please also update heapdump.c:dumproots. + switch i { + case _RootData: + scanblock(uintptr(unsafe.Pointer(&data)), uintptr(unsafe.Pointer(&edata))-uintptr(unsafe.Pointer(&data)), gcdatamask.bytedata) + + case _RootBss: + scanblock(uintptr(unsafe.Pointer(&bss)), uintptr(unsafe.Pointer(&ebss))-uintptr(unsafe.Pointer(&bss)), gcbssmask.bytedata) + + case _RootFinalizers: + for fb := allfin; fb != nil; fb = fb.alllink { + scanblock(uintptr(unsafe.Pointer(&fb.fin[0])), uintptr(fb.cnt)*unsafe.Sizeof(fb.fin[0]), &finptrmask[0]) + } + + case _RootSpans: + // mark MSpan.specials + sg := mheap_.sweepgen + for spanidx := uint32(0); spanidx < uint32(len(work.spans)); spanidx++ { + s := work.spans[spanidx] + if s.state != mSpanInUse { + continue + } + if s.sweepgen != sg { + print("sweep ", s.sweepgen, " ", sg, "\n") + gothrow("gc: unswept span") + } + for sp := s.specials; sp != nil; sp = sp.next { + if sp.kind != _KindSpecialFinalizer { + continue + } + // don't mark finalized object, but scan it so we + // retain everything it points to. + spf := (*specialfinalizer)(unsafe.Pointer(sp)) + // A finalizer can be set for an inner byte of an object, find object beginning. + p := uintptr(s.start<<_PageShift) + uintptr(spf.special.offset)/s.elemsize*s.elemsize + scanblock(p, s.elemsize, nil) + scanblock(uintptr(unsafe.Pointer(&spf.fn)), ptrSize, &oneptr[0]) + } + } + + case _RootFlushCaches: + flushallmcaches() + + default: + // the rest is scanning goroutine stacks + if uintptr(i-_RootCount) >= allglen { + gothrow("markroot: bad index") + } + gp := allgs[i-_RootCount] + // remember when we've first observed the G blocked + // needed only to output in traceback + status := readgstatus(gp) + if (status == _Gwaiting || status == _Gsyscall) && gp.waitsince == 0 { + gp.waitsince = work.tstart + } + // Shrink a stack if not much of it is being used. + shrinkstack(gp) + if readgstatus(gp) == _Gdead { + gp.gcworkdone = true + } else { + gp.gcworkdone = false + } + restart := stopg(gp) + scanstack(gp) + if restart { + restartg(gp) + } + } +} + +// Get an empty work buffer off the work.empty list, +// allocating new buffers as needed. +func getempty(b *workbuf) *workbuf { + _g_ := getg() + if b != nil { + lfstackpush(&work.full, &b.node) + } + b = nil + c := _g_.m.mcache + if c.gcworkbuf != nil { + b = (*workbuf)(c.gcworkbuf) + c.gcworkbuf = nil + } + if b == nil { + b = (*workbuf)(lfstackpop(&work.empty)) + } + if b == nil { + b = (*workbuf)(persistentalloc(unsafe.Sizeof(*b), _CacheLineSize, &memstats.gc_sys)) + } + b.nobj = 0 + return b +} + +func putempty(b *workbuf) { + _g_ := getg() + c := _g_.m.mcache + if c.gcworkbuf == nil { + c.gcworkbuf = (unsafe.Pointer)(b) + return + } + lfstackpush(&work.empty, &b.node) +} + +func gcworkbuffree(b unsafe.Pointer) { + if b != nil { + putempty((*workbuf)(b)) + } +} + +// Get a full work buffer off the work.full list, or return nil. +func getfull(b *workbuf) *workbuf { + if b != nil { + lfstackpush(&work.empty, &b.node) + } + b = (*workbuf)(lfstackpop(&work.full)) + if b != nil || work.nproc == 1 { + return b + } + + xadd(&work.nwait, +1) + for i := 0; ; i++ { + if work.full != 0 { + xadd(&work.nwait, -1) + b = (*workbuf)(lfstackpop(&work.full)) + if b != nil { + return b + } + xadd(&work.nwait, +1) + } + if work.nwait == work.nproc { + return nil + } + _g_ := getg() + if i < 10 { + _g_.m.gcstats.nprocyield++ + procyield(20) + } else if i < 20 { + _g_.m.gcstats.nosyield++ + osyield() + } else { + _g_.m.gcstats.nsleep++ + usleep(100) + } + } +} + +func handoff(b *workbuf) *workbuf { + // Make new buffer with half of b's pointers. + b1 := getempty(nil) + n := b.nobj / 2 + b.nobj -= n + b1.nobj = n + memmove(unsafe.Pointer(&b1.obj[0]), unsafe.Pointer(&b.obj[b.nobj]), n*unsafe.Sizeof(b1.obj[0])) + _g_ := getg() + _g_.m.gcstats.nhandoff++ + _g_.m.gcstats.nhandoffcnt += uint64(n) + + // Put b on full list - let first half of b get stolen. + lfstackpush(&work.full, &b.node) + return b1 +} + +func stackmapdata(stkmap *stackmap, n int32) bitvector { + if n < 0 || n >= stkmap.n { + gothrow("stackmapdata: index out of range") + } + return bitvector{stkmap.nbit, (*byte)(add(unsafe.Pointer(&stkmap.bytedata), uintptr(n*((stkmap.nbit+31)/32*4))))} +} + +// Scan a stack frame: local variables and function arguments/results. +func scanframe(frame *stkframe, unused unsafe.Pointer) bool { + + f := frame.fn + targetpc := frame.continpc + if targetpc == 0 { + // Frame is dead. + return true + } + if _DebugGC > 1 { + print("scanframe ", gofuncname(f), "\n") + } + if targetpc != f.entry { + targetpc-- + } + pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc) + if pcdata == -1 { + // We do not have a valid pcdata value but there might be a + // stackmap for this function. It is likely that we are looking + // at the function prologue, assume so and hope for the best. + pcdata = 0 + } + + // Scan local variables if stack frame has been allocated. + size := frame.varp - frame.sp + var minsize uintptr + if thechar != '6' && thechar != '8' { + minsize = ptrSize + } else { + minsize = 0 + } + if size > minsize { + stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps)) + if stkmap == nil || stkmap.n <= 0 { + print("runtime: frame ", gofuncname(f), " untyped locals ", hex(frame.varp-size), "+", hex(size), "\n") + gothrow("missing stackmap") + } + + // Locals bitmap information, scan just the pointers in locals. + if pcdata < 0 || pcdata >= stkmap.n { + // don't know where we are + print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " locals stack map entries for ", gofuncname(f), " (targetpc=", targetpc, ")\n") + gothrow("scanframe: bad symbol table") + } + bv := stackmapdata(stkmap, pcdata) + size = (uintptr(bv.n) * ptrSize) / bitsPerPointer + scanblock(frame.varp-size, uintptr(bv.n)/bitsPerPointer*ptrSize, bv.bytedata) + } + + // Scan arguments. + if frame.arglen > 0 { + var bv bitvector + if frame.argmap != nil { + bv = *frame.argmap + } else { + stkmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps)) + if stkmap == nil || stkmap.n <= 0 { + print("runtime: frame ", gofuncname(f), " untyped args ", hex(frame.argp), "+", hex(frame.arglen), "\n") + gothrow("missing stackmap") + } + if pcdata < 0 || pcdata >= stkmap.n { + // don't know where we are + print("runtime: pcdata is ", pcdata, " and ", stkmap.n, " args stack map entries for ", gofuncname(f), " (targetpc=", targetpc, ")\n") + gothrow("scanframe: bad symbol table") + } + bv = stackmapdata(stkmap, pcdata) + } + scanblock(frame.argp, uintptr(bv.n)/bitsPerPointer*ptrSize, bv.bytedata) + } + return true +} + +func scanstack(gp *g) { + // TODO(rsc): Due to a precedence error, this was never checked in the original C version. + // If you enable the check, the gothrow happens. + /* + if readgstatus(gp)&_Gscan == 0 { + print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + gothrow("mark - bad status") + } + */ + + switch readgstatus(gp) &^ _Gscan { + default: + print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + gothrow("mark - bad status") + case _Gdead: + return + case _Grunning: + print("runtime: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + gothrow("mark - world not stopped") + case _Grunnable, _Gsyscall, _Gwaiting: + // ok + } + + if gp == getg() { + gothrow("can't scan our own stack") + } + mp := gp.m + if mp != nil && mp.helpgc != 0 { + gothrow("can't scan gchelper stack") + } + + gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0) + tracebackdefers(gp, scanframe, nil) +} + +// The gp has been moved to a gc safepoint. If there is gcphase specific +// work it is done here. +func gcphasework(gp *g) { + switch gcphase { + default: + gothrow("gcphasework in bad gcphase") + case _GCoff, _GCquiesce, _GCstw, _GCsweep: + // No work for now. + case _GCmark: + // Disabled until concurrent GC is implemented + // but indicate the scan has been done. + // scanstack(gp); + } + gp.gcworkdone = true +} + +var finalizer1 = [...]byte{ + // Each Finalizer is 5 words, ptr ptr uintptr ptr ptr. + // Each byte describes 4 words. + // Need 4 Finalizers described by 5 bytes before pattern repeats: + // ptr ptr uintptr ptr ptr + // ptr ptr uintptr ptr ptr + // ptr ptr uintptr ptr ptr + // ptr ptr uintptr ptr ptr + // aka + // ptr ptr uintptr ptr + // ptr ptr ptr uintptr + // ptr ptr ptr ptr + // uintptr ptr ptr ptr + // ptr uintptr ptr ptr + // Assumptions about Finalizer layout checked below. + bitsPointer | bitsPointer<<2 | bitsScalar<<4 | bitsPointer<<6, + bitsPointer | bitsPointer<<2 | bitsPointer<<4 | bitsScalar<<6, + bitsPointer | bitsPointer<<2 | bitsPointer<<4 | bitsPointer<<6, + bitsScalar | bitsPointer<<2 | bitsPointer<<4 | bitsPointer<<6, + bitsPointer | bitsScalar<<2 | bitsPointer<<4 | bitsPointer<<6, +} + +func queuefinalizer(p unsafe.Pointer, fn *funcval, nret uintptr, fint *_type, ot *ptrtype) { + lock(&finlock) + if finq == nil || finq.cnt == finq.cap { + if finc == nil { + finc = (*finblock)(persistentalloc(_FinBlockSize, 0, &memstats.gc_sys)) + finc.cap = int32((_FinBlockSize-unsafe.Sizeof(finblock{}))/unsafe.Sizeof(finalizer{}) + 1) + finc.alllink = allfin + allfin = finc + if finptrmask[0] == 0 { + // Build pointer mask for Finalizer array in block. + // Check assumptions made in finalizer1 array above. + if (unsafe.Sizeof(finalizer{}) != 5*ptrSize || + unsafe.Offsetof(finalizer{}.fn) != 0 || + unsafe.Offsetof(finalizer{}.arg) != ptrSize || + unsafe.Offsetof(finalizer{}.nret) != 2*ptrSize || + unsafe.Offsetof(finalizer{}.fint) != 3*ptrSize || + unsafe.Offsetof(finalizer{}.ot) != 4*ptrSize || + bitsPerPointer != 2) { + gothrow("finalizer out of sync") + } + for i := range finptrmask { + finptrmask[i] = finalizer1[i%len(finalizer1)] + } + } + } + block := finc + finc = block.next + block.next = finq + finq = block + } + f := (*finalizer)(add(unsafe.Pointer(&finq.fin[0]), uintptr(finq.cnt)*unsafe.Sizeof(finq.fin[0]))) + finq.cnt++ + f.fn = fn + f.nret = nret + f.fint = fint + f.ot = ot + f.arg = p + fingwake = true + unlock(&finlock) +} + +func iterate_finq(callback func(*funcval, unsafe.Pointer, uintptr, *_type, *ptrtype)) { + for fb := allfin; fb != nil; fb = fb.alllink { + for i := int32(0); i < fb.cnt; i++ { + f := &fb.fin[i] + callback(f.fn, f.arg, f.nret, f.fint, f.ot) + } + } +} + +func mSpan_EnsureSwept(s *mspan) { + // Caller must disable preemption. + // Otherwise when this function returns the span can become unswept again + // (if GC is triggered on another goroutine). + _g_ := getg() + if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 { + gothrow("MSpan_EnsureSwept: m is not locked") + } + + sg := mheap_.sweepgen + if atomicload(&s.sweepgen) == sg { + return + } + if cas(&s.sweepgen, sg-2, sg-1) { + mSpan_Sweep(s, false) + return + } + // unfortunate condition, and we don't have efficient means to wait + for atomicload(&s.sweepgen) != sg { + osyield() + } +} + +// Sweep frees or collects finalizers for blocks not marked in the mark phase. +// It clears the mark bits in preparation for the next GC round. +// Returns true if the span was returned to heap. +// If preserve=true, don't return it to heap nor relink in MCentral lists; +// caller takes care of it. +func mSpan_Sweep(s *mspan, preserve bool) bool { + // It's critical that we enter this function with preemption disabled, + // GC must not start while we are in the middle of this function. + _g_ := getg() + if _g_.m.locks == 0 && _g_.m.mallocing == 0 && _g_ != _g_.m.g0 { + gothrow("MSpan_Sweep: m is not locked") + } + sweepgen := mheap_.sweepgen + if s.state != mSpanInUse || s.sweepgen != sweepgen-1 { + print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n") + gothrow("MSpan_Sweep: bad span state") + } + arena_start := mheap_.arena_start + cl := s.sizeclass + size := s.elemsize + var n int32 + var npages int32 + if cl == 0 { + n = 1 + } else { + // Chunk full of small blocks. + npages = class_to_allocnpages[cl] + n = (npages << _PageShift) / int32(size) + } + res := false + nfree := 0 + var head mlink + end := &head + c := _g_.m.mcache + sweepgenset := false + + // Mark any free objects in this span so we don't collect them. + for link := s.freelist; link != nil; link = link.next { + off := (uintptr(unsafe.Pointer(link)) - arena_start) / ptrSize + bitp := arena_start - off/wordsPerBitmapByte - 1 + shift := (off % wordsPerBitmapByte) * gcBits + *(*byte)(unsafe.Pointer(bitp)) |= bitMarked << shift + } + + // Unlink & free special records for any objects we're about to free. + specialp := &s.specials + special := *specialp + for special != nil { + // A finalizer can be set for an inner byte of an object, find object beginning. + p := uintptr(s.start<<_PageShift) + uintptr(special.offset)/size*size + off := (p - arena_start) / ptrSize + bitp := arena_start - off/wordsPerBitmapByte - 1 + shift := (off % wordsPerBitmapByte) * gcBits + bits := (*(*byte)(unsafe.Pointer(bitp)) >> shift) & bitMask + if bits&bitMarked == 0 { + // Find the exact byte for which the special was setup + // (as opposed to object beginning). + p := uintptr(s.start<<_PageShift) + uintptr(special.offset) + // about to free object: splice out special record + y := special + special = special.next + *specialp = special + if !freespecial(y, unsafe.Pointer(p), size, false) { + // stop freeing of object if it has a finalizer + *(*byte)(unsafe.Pointer(bitp)) |= bitMarked << shift + } + } else { + // object is still live: keep special record + specialp = &special.next + special = *specialp + } + } + + // Sweep through n objects of given size starting at p. + // This thread owns the span now, so it can manipulate + // the block bitmap without atomic operations. + p := uintptr(s.start << _PageShift) + off := (p - arena_start) / ptrSize + bitp := arena_start - off/wordsPerBitmapByte - 1 + shift := uint(0) + step := size / (ptrSize * wordsPerBitmapByte) + // Rewind to the previous quadruple as we move to the next + // in the beginning of the loop. + bitp += step + if step == 0 { + // 8-byte objects. + bitp++ + shift = gcBits + } + for ; n > 0; n, p = n-1, p+size { + bitp -= step + if step == 0 { + if shift != 0 { + bitp-- + } + shift = gcBits - shift + } + + xbits := *(*byte)(unsafe.Pointer(bitp)) + bits := (xbits >> shift) & bitMask + + // Allocated and marked object, reset bits to allocated. + if bits&bitMarked != 0 { + *(*byte)(unsafe.Pointer(bitp)) &^= bitMarked << shift + continue + } + + // At this point we know that we are looking at garbage object + // that needs to be collected. + if debug.allocfreetrace != 0 { + tracefree(unsafe.Pointer(p), size) + } + + // Reset to allocated+noscan. + *(*byte)(unsafe.Pointer(bitp)) = uint8(uintptr(xbits&^((bitMarked|bitsMask<<2)<<shift)) | uintptr(bitsDead)<<(shift+2)) + if cl == 0 { + // Free large span. + if preserve { + gothrow("can't preserve large span") + } + unmarkspan(p, s.npages<<_PageShift) + s.needzero = 1 + + // important to set sweepgen before returning it to heap + atomicstore(&s.sweepgen, sweepgen) + sweepgenset = true + + // NOTE(rsc,dvyukov): The original implementation of efence + // in CL 22060046 used SysFree instead of SysFault, so that + // the operating system would eventually give the memory + // back to us again, so that an efence program could run + // longer without running out of memory. Unfortunately, + // calling SysFree here without any kind of adjustment of the + // heap data structures means that when the memory does + // come back to us, we have the wrong metadata for it, either in + // the MSpan structures or in the garbage collection bitmap. + // Using SysFault here means that the program will run out of + // memory fairly quickly in efence mode, but at least it won't + // have mysterious crashes due to confused memory reuse. + // It should be possible to switch back to SysFree if we also + // implement and then call some kind of MHeap_DeleteSpan. + if debug.efence > 0 { + s.limit = 0 // prevent mlookup from finding this span + sysFault(unsafe.Pointer(p), size) + } else { + mHeap_Free(&mheap_, s, 1) + } + c.local_nlargefree++ + c.local_largefree += size + xadd64(&memstats.next_gc, -int64(size)*int64(gcpercent+100)/100) + res = true + } else { + // Free small object. + if size > 2*ptrSize { + *(*uintptr)(unsafe.Pointer(p + ptrSize)) = uintptrMask & 0xdeaddeaddeaddead // mark as "needs to be zeroed" + } else if size > ptrSize { + *(*uintptr)(unsafe.Pointer(p + ptrSize)) = 0 + } + end.next = (*mlink)(unsafe.Pointer(p)) + end = end.next + nfree++ + } + } + + // We need to set s.sweepgen = h.sweepgen only when all blocks are swept, + // because of the potential for a concurrent free/SetFinalizer. + // But we need to set it before we make the span available for allocation + // (return it to heap or mcentral), because allocation code assumes that a + // span is already swept if available for allocation. + if !sweepgenset && nfree == 0 { + // The span must be in our exclusive ownership until we update sweepgen, + // check for potential races. + if s.state != mSpanInUse || s.sweepgen != sweepgen-1 { + print("MSpan_Sweep: state=", s.state, " sweepgen=", s.sweepgen, " mheap.sweepgen=", sweepgen, "\n") + gothrow("MSpan_Sweep: bad span state after sweep") + } + atomicstore(&s.sweepgen, sweepgen) + } + if nfree > 0 { + c.local_nsmallfree[cl] += uintptr(nfree) + c.local_cachealloc -= intptr(uintptr(nfree) * size) + xadd64(&memstats.next_gc, -int64(nfree)*int64(size)*int64(gcpercent+100)/100) + res = mCentral_FreeSpan(&mheap_.central[cl].mcentral, s, int32(nfree), head.next, end, preserve) + // MCentral_FreeSpan updates sweepgen + } + return res +} + +// State of background sweep. +// Protected by gclock. +type sweepdata struct { + g *g + parked bool + started bool + + spanidx uint32 // background sweeper position + + nbgsweep uint32 + npausesweep uint32 +} + +var sweep sweepdata + +// sweeps one span +// returns number of pages returned to heap, or ^uintptr(0) if there is nothing to sweep +func sweepone() uintptr { + _g_ := getg() + + // increment locks to ensure that the goroutine is not preempted + // in the middle of sweep thus leaving the span in an inconsistent state for next GC + _g_.m.locks++ + sg := mheap_.sweepgen + for { + idx := xadd(&sweep.spanidx, 1) - 1 + if idx >= uint32(len(work.spans)) { + mheap_.sweepdone = 1 + _g_.m.locks-- + return ^uintptr(0) + } + s := work.spans[idx] + if s.state != mSpanInUse { + s.sweepgen = sg + continue + } + if s.sweepgen != sg-2 || !cas(&s.sweepgen, sg-2, sg-1) { + continue + } + npages := s.npages + if !mSpan_Sweep(s, false) { + npages = 0 + } + _g_.m.locks-- + return npages + } +} + +func gosweepone() uintptr { + var ret uintptr + systemstack(func() { + ret = sweepone() + }) + return ret +} + +func gosweepdone() bool { + return mheap_.sweepdone != 0 +} + +func gchelper() { + _g_ := getg() + _g_.m.traceback = 2 + gchelperstart() + + // parallel mark for over gc roots + parfordo(work.markfor) + + // help other threads scan secondary blocks + scanblock(0, 0, nil) + + nproc := work.nproc // work.nproc can change right after we increment work.ndone + if xadd(&work.ndone, +1) == nproc-1 { + notewakeup(&work.alldone) + } + _g_.m.traceback = 0 +} + +func cachestats() { + for i := 0; ; i++ { + p := allp[i] + if p == nil { + break + } + c := p.mcache + if c == nil { + continue + } + purgecachedstats(c) + } +} + +func flushallmcaches() { + for i := 0; ; i++ { + p := allp[i] + if p == nil { + break + } + c := p.mcache + if c == nil { + continue + } + mCache_ReleaseAll(c) + stackcache_clear(c) + } +} + +func updatememstats(stats *gcstats) { + if stats != nil { + *stats = gcstats{} + } + for mp := allm; mp != nil; mp = mp.alllink { + if stats != nil { + src := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(&mp.gcstats)) + dst := (*[unsafe.Sizeof(gcstats{}) / 8]uint64)(unsafe.Pointer(stats)) + for i, v := range src { + dst[i] += v + } + mp.gcstats = gcstats{} + } + } + + memstats.mcache_inuse = uint64(mheap_.cachealloc.inuse) + memstats.mspan_inuse = uint64(mheap_.spanalloc.inuse) + memstats.sys = memstats.heap_sys + memstats.stacks_sys + memstats.mspan_sys + + memstats.mcache_sys + memstats.buckhash_sys + memstats.gc_sys + memstats.other_sys + + // Calculate memory allocator stats. + // During program execution we only count number of frees and amount of freed memory. + // Current number of alive object in the heap and amount of alive heap memory + // are calculated by scanning all spans. + // Total number of mallocs is calculated as number of frees plus number of alive objects. + // Similarly, total amount of allocated memory is calculated as amount of freed memory + // plus amount of alive heap memory. + memstats.alloc = 0 + memstats.total_alloc = 0 + memstats.nmalloc = 0 + memstats.nfree = 0 + for i := 0; i < len(memstats.by_size); i++ { + memstats.by_size[i].nmalloc = 0 + memstats.by_size[i].nfree = 0 + } + + // Flush MCache's to MCentral. + systemstack(flushallmcaches) + + // Aggregate local stats. + cachestats() + + // Scan all spans and count number of alive objects. + lock(&mheap_.lock) + for i := uint32(0); i < mheap_.nspan; i++ { + s := h_allspans[i] + if s.state != mSpanInUse { + continue + } + if s.sizeclass == 0 { + memstats.nmalloc++ + memstats.alloc += uint64(s.elemsize) + } else { + memstats.nmalloc += uint64(s.ref) + memstats.by_size[s.sizeclass].nmalloc += uint64(s.ref) + memstats.alloc += uint64(s.ref) * uint64(s.elemsize) + } + } + unlock(&mheap_.lock) + + // Aggregate by size class. + smallfree := uint64(0) + memstats.nfree = mheap_.nlargefree + for i := 0; i < len(memstats.by_size); i++ { + memstats.nfree += mheap_.nsmallfree[i] + memstats.by_size[i].nfree = mheap_.nsmallfree[i] + memstats.by_size[i].nmalloc += mheap_.nsmallfree[i] + smallfree += uint64(mheap_.nsmallfree[i]) * uint64(class_to_size[i]) + } + memstats.nfree += memstats.tinyallocs + memstats.nmalloc += memstats.nfree + + // Calculate derived stats. + memstats.total_alloc = uint64(memstats.alloc) + uint64(mheap_.largefree) + smallfree + memstats.heap_alloc = memstats.alloc + memstats.heap_objects = memstats.nmalloc - memstats.nfree +} + +func gcinit() { + if unsafe.Sizeof(workbuf{}) != _WorkbufSize { + gothrow("runtime: size of Workbuf is suboptimal") + } + + work.markfor = parforalloc(_MaxGcproc) + gcpercent = readgogc() + gcdatamask = unrollglobgcprog((*byte)(unsafe.Pointer(&gcdata)), uintptr(unsafe.Pointer(&edata))-uintptr(unsafe.Pointer(&data))) + gcbssmask = unrollglobgcprog((*byte)(unsafe.Pointer(&gcbss)), uintptr(unsafe.Pointer(&ebss))-uintptr(unsafe.Pointer(&bss))) +} + +func gc_m(start_time int64, eagersweep bool) { + _g_ := getg() + gp := _g_.m.curg + casgstatus(gp, _Grunning, _Gwaiting) + gp.waitreason = "garbage collection" + + gc(start_time, eagersweep) + + if nbadblock > 0 { + // Work out path from root to bad block. + for { + gc(start_time, eagersweep) + if nbadblock >= int32(len(badblock)) { + gothrow("cannot find path to bad pointer") + } + } + } + + casgstatus(gp, _Gwaiting, _Grunning) +} + +func gc(start_time int64, eagersweep bool) { + if _DebugGCPtrs { + print("GC start\n") + } + + if debug.allocfreetrace > 0 { + tracegc() + } + + _g_ := getg() + _g_.m.traceback = 2 + t0 := start_time + work.tstart = start_time + + var t1 int64 + if debug.gctrace > 0 { + t1 = nanotime() + } + + // Sweep what is not sweeped by bgsweep. + for sweepone() != ^uintptr(0) { + sweep.npausesweep++ + } + + // Cache runtime.mheap_.allspans in work.spans to avoid conflicts with + // resizing/freeing allspans. + // New spans can be created while GC progresses, but they are not garbage for + // this round: + // - new stack spans can be created even while the world is stopped. + // - new malloc spans can be created during the concurrent sweep + + // Even if this is stop-the-world, a concurrent exitsyscall can allocate a stack from heap. + lock(&mheap_.lock) + // Free the old cached sweep array if necessary. + if work.spans != nil && &work.spans[0] != &h_allspans[0] { + sysFree(unsafe.Pointer(&work.spans[0]), uintptr(len(work.spans))*unsafe.Sizeof(work.spans[0]), &memstats.other_sys) + } + // Cache the current array for marking. + mheap_.gcspans = mheap_.allspans + work.spans = h_allspans + unlock(&mheap_.lock) + + work.nwait = 0 + work.ndone = 0 + work.nproc = uint32(gcprocs()) + parforsetup(work.markfor, work.nproc, uint32(_RootCount+allglen), nil, false, markroot) + if work.nproc > 1 { + noteclear(&work.alldone) + helpgc(int32(work.nproc)) + } + + var t2 int64 + if debug.gctrace > 0 { + t2 = nanotime() + } + + gchelperstart() + parfordo(work.markfor) + scanblock(0, 0, nil) + + var t3 int64 + if debug.gctrace > 0 { + t3 = nanotime() + } + + if work.nproc > 1 { + notesleep(&work.alldone) + } + + shrinkfinish() + + cachestats() + // next_gc calculation is tricky with concurrent sweep since we don't know size of live heap + // estimate what was live heap size after previous GC (for printing only) + heap0 := memstats.next_gc * 100 / (uint64(gcpercent) + 100) + // conservatively set next_gc to high value assuming that everything is live + // concurrent/lazy sweep will reduce this number while discovering new garbage + memstats.next_gc = memstats.heap_alloc + memstats.heap_alloc*uint64(gcpercent)/100 + + t4 := nanotime() + atomicstore64(&memstats.last_gc, uint64(unixnanotime())) // must be Unix time to make sense to user + memstats.pause_ns[memstats.numgc%uint32(len(memstats.pause_ns))] = uint64(t4 - t0) + memstats.pause_end[memstats.numgc%uint32(len(memstats.pause_end))] = uint64(t4) + memstats.pause_total_ns += uint64(t4 - t0) + memstats.numgc++ + if memstats.debuggc { + print("pause ", t4-t0, "\n") + } + + if debug.gctrace > 0 { + heap1 := memstats.heap_alloc + var stats gcstats + updatememstats(&stats) + if heap1 != memstats.heap_alloc { + print("runtime: mstats skew: heap=", heap1, "/", memstats.heap_alloc, "\n") + gothrow("mstats skew") + } + obj := memstats.nmalloc - memstats.nfree + + stats.nprocyield += work.markfor.nprocyield + stats.nosyield += work.markfor.nosyield + stats.nsleep += work.markfor.nsleep + + print("gc", memstats.numgc, "(", work.nproc, "): ", + (t1-t0)/1000, "+", (t2-t1)/1000, "+", (t3-t2)/1000, "+", (t4-t3)/1000, " us, ", + heap0>>20, " -> ", heap1>>20, " MB, ", + obj, " (", memstats.nmalloc, "-", memstats.nfree, ") objects, ", + gcount(), " goroutines, ", + len(work.spans), "/", sweep.nbgsweep, "/", sweep.npausesweep, " sweeps, ", + stats.nhandoff, "(", stats.nhandoffcnt, ") handoff, ", + work.markfor.nsteal, "(", work.markfor.nstealcnt, ") steal, ", + stats.nprocyield, "/", stats.nosyield, "/", stats.nsleep, " yields\n") + sweep.nbgsweep = 0 + sweep.npausesweep = 0 + } + + // See the comment in the beginning of this function as to why we need the following. + // Even if this is still stop-the-world, a concurrent exitsyscall can allocate a stack from heap. + lock(&mheap_.lock) + // Free the old cached mark array if necessary. + if work.spans != nil && &work.spans[0] != &h_allspans[0] { + sysFree(unsafe.Pointer(&work.spans[0]), uintptr(len(work.spans))*unsafe.Sizeof(work.spans[0]), &memstats.other_sys) + } + + // Cache the current array for sweeping. + mheap_.gcspans = mheap_.allspans + mheap_.sweepgen += 2 + mheap_.sweepdone = 0 + work.spans = h_allspans + sweep.spanidx = 0 + unlock(&mheap_.lock) + + if _ConcurrentSweep && !eagersweep { + lock(&gclock) + if !sweep.started { + go bgsweep() + sweep.started = true + } else if sweep.parked { + sweep.parked = false + ready(sweep.g) + } + unlock(&gclock) + } else { + // Sweep all spans eagerly. + for sweepone() != ^uintptr(0) { + sweep.npausesweep++ + } + // Do an additional mProf_GC, because all 'free' events are now real as well. + mProf_GC() + } + + mProf_GC() + _g_.m.traceback = 0 + + if _DebugGCPtrs { + print("GC end\n") + } +} + +func readmemstats_m(stats *MemStats) { + updatememstats(nil) + + // Size of the trailing by_size array differs between Go and C, + // NumSizeClasses was changed, but we can not change Go struct because of backward compatibility. + memmove(unsafe.Pointer(stats), unsafe.Pointer(&memstats), sizeof_C_MStats) + + // Stack numbers are part of the heap numbers, separate those out for user consumption + stats.StackSys = stats.StackInuse + stats.HeapInuse -= stats.StackInuse + stats.HeapSys -= stats.StackInuse +} + +//go:linkname readGCStats runtime/debug.readGCStats +func readGCStats(pauses *[]uint64) { + systemstack(func() { + readGCStats_m(pauses) + }) +} + +func readGCStats_m(pauses *[]uint64) { + p := *pauses + // Calling code in runtime/debug should make the slice large enough. + if cap(p) < len(memstats.pause_ns)+3 { + gothrow("runtime: short slice passed to readGCStats") + } + + // Pass back: pauses, pause ends, last gc (absolute time), number of gc, total pause ns. + lock(&mheap_.lock) + + n := memstats.numgc + if n > uint32(len(memstats.pause_ns)) { + n = uint32(len(memstats.pause_ns)) + } + + // The pause buffer is circular. The most recent pause is at + // pause_ns[(numgc-1)%len(pause_ns)], and then backward + // from there to go back farther in time. We deliver the times + // most recent first (in p[0]). + p = p[:cap(p)] + for i := uint32(0); i < n; i++ { + j := (memstats.numgc - 1 - i) % uint32(len(memstats.pause_ns)) + p[i] = memstats.pause_ns[j] + p[n+i] = memstats.pause_end[j] + } + + p[n+n] = memstats.last_gc + p[n+n+1] = uint64(memstats.numgc) + p[n+n+2] = memstats.pause_total_ns + unlock(&mheap_.lock) + *pauses = p[:n+n+3] +} + +func setGCPercent(in int32) (out int32) { + lock(&mheap_.lock) + out = gcpercent + if in < 0 { + in = -1 + } + gcpercent = in + unlock(&mheap_.lock) + return out +} + +func gchelperstart() { + _g_ := getg() + + if _g_.m.helpgc < 0 || _g_.m.helpgc >= _MaxGcproc { + gothrow("gchelperstart: bad m->helpgc") + } + if _g_ != _g_.m.g0 { + gothrow("gchelper not running on g0 stack") + } +} + +func wakefing() *g { + var res *g + lock(&finlock) + if fingwait && fingwake { + fingwait = false + fingwake = false + res = fing + } + unlock(&finlock) + return res +} + +func addb(p *byte, n uintptr) *byte { + return (*byte)(add(unsafe.Pointer(p), n)) +} + +// Recursively unrolls GC program in prog. +// mask is where to store the result. +// ppos is a pointer to position in mask, in bits. +// sparse says to generate 4-bits per word mask for heap (2-bits for data/bss otherwise). +func unrollgcprog1(maskp *byte, prog *byte, ppos *uintptr, inplace, sparse bool) *byte { + arena_start := mheap_.arena_start + pos := *ppos + mask := (*[1 << 30]byte)(unsafe.Pointer(maskp)) + for { + switch *prog { + default: + gothrow("unrollgcprog: unknown instruction") + + case insData: + prog = addb(prog, 1) + siz := int(*prog) + prog = addb(prog, 1) + p := (*[1 << 30]byte)(unsafe.Pointer(prog)) + for i := 0; i < siz; i++ { + v := p[i/_PointersPerByte] + v >>= (uint(i) % _PointersPerByte) * _BitsPerPointer + v &= _BitsMask + if inplace { + // Store directly into GC bitmap. + off := (uintptr(unsafe.Pointer(&mask[pos])) - arena_start) / ptrSize + bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1)) + shift := (off % wordsPerBitmapByte) * gcBits + if shift == 0 { + *bitp = 0 + } + *bitp |= v << (shift + 2) + pos += ptrSize + } else if sparse { + // 4-bits per word + v <<= (pos % 8) + 2 + mask[pos/8] |= v + pos += gcBits + } else { + // 2-bits per word + v <<= pos % 8 + mask[pos/8] |= v + pos += _BitsPerPointer + } + } + prog = addb(prog, round(uintptr(siz)*_BitsPerPointer, 8)/8) + + case insArray: + prog = (*byte)(add(unsafe.Pointer(prog), 1)) + siz := uintptr(0) + for i := uintptr(0); i < ptrSize; i++ { + siz = (siz << 8) + uintptr(*(*byte)(add(unsafe.Pointer(prog), ptrSize-i-1))) + } + prog = (*byte)(add(unsafe.Pointer(prog), ptrSize)) + var prog1 *byte + for i := uintptr(0); i < siz; i++ { + prog1 = unrollgcprog1(&mask[0], prog, &pos, inplace, sparse) + } + if *prog1 != insArrayEnd { + gothrow("unrollgcprog: array does not end with insArrayEnd") + } + prog = (*byte)(add(unsafe.Pointer(prog1), 1)) + + case insArrayEnd, insEnd: + *ppos = pos + return prog + } + } +} + +// Unrolls GC program prog for data/bss, returns dense GC mask. +func unrollglobgcprog(prog *byte, size uintptr) bitvector { + masksize := round(round(size, ptrSize)/ptrSize*bitsPerPointer, 8) / 8 + mask := (*[1 << 30]byte)(persistentalloc(masksize+1, 0, &memstats.gc_sys)) + mask[masksize] = 0xa1 + pos := uintptr(0) + prog = unrollgcprog1(&mask[0], prog, &pos, false, false) + if pos != size/ptrSize*bitsPerPointer { + print("unrollglobgcprog: bad program size, got ", pos, ", expect ", size/ptrSize*bitsPerPointer, "\n") + gothrow("unrollglobgcprog: bad program size") + } + if *prog != insEnd { + gothrow("unrollglobgcprog: program does not end with insEnd") + } + if mask[masksize] != 0xa1 { + gothrow("unrollglobgcprog: overflow") + } + return bitvector{int32(masksize * 8), &mask[0]} +} + +func unrollgcproginplace_m(v unsafe.Pointer, typ *_type, size, size0 uintptr) { + pos := uintptr(0) + prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1]))) + for pos != size0 { + unrollgcprog1((*byte)(v), prog, &pos, true, true) + } + + // Mark first word as bitAllocated. + arena_start := mheap_.arena_start + off := (uintptr(v) - arena_start) / ptrSize + bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1)) + shift := (off % wordsPerBitmapByte) * gcBits + *bitp |= bitBoundary << shift + + // Mark word after last as BitsDead. + if size0 < size { + off := (uintptr(v) + size0 - arena_start) / ptrSize + bitp := (*byte)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1)) + shift := (off % wordsPerBitmapByte) * gcBits + *bitp &= uint8(^(bitPtrMask << shift) | uintptr(bitsDead)<<(shift+2)) + } +} + +var unroll mutex + +// Unrolls GC program in typ.gc[1] into typ.gc[0] +func unrollgcprog_m(typ *_type) { + lock(&unroll) + mask := (*byte)(unsafe.Pointer(uintptr(typ.gc[0]))) + if *mask == 0 { + pos := uintptr(8) // skip the unroll flag + prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1]))) + prog = unrollgcprog1(mask, prog, &pos, false, true) + if *prog != insEnd { + gothrow("unrollgcprog: program does not end with insEnd") + } + if typ.size/ptrSize%2 != 0 { + // repeat the program + prog := (*byte)(unsafe.Pointer(uintptr(typ.gc[1]))) + unrollgcprog1(mask, prog, &pos, false, true) + } + + // atomic way to say mask[0] = 1 + atomicor8(mask, 1) + } + unlock(&unroll) +} + +// mark the span of memory at v as having n blocks of the given size. +// if leftover is true, there is left over space at the end of the span. +func markspan(v unsafe.Pointer, size uintptr, n uintptr, leftover bool) { + if uintptr(v)+size*n > mheap_.arena_used || uintptr(v) < mheap_.arena_start { + gothrow("markspan: bad pointer") + } + + // Find bits of the beginning of the span. + off := (uintptr(v) - uintptr(mheap_.arena_start)) / ptrSize + if off%wordsPerBitmapByte != 0 { + gothrow("markspan: unaligned length") + } + b := mheap_.arena_start - off/wordsPerBitmapByte - 1 + + // Okay to use non-atomic ops here, because we control + // the entire span, and each bitmap byte has bits for only + // one span, so no other goroutines are changing these bitmap words. + + if size == ptrSize { + // Possible only on 64-bits (minimal size class is 8 bytes). + // Set memory to 0x11. + if (bitBoundary|bitsDead)<<gcBits|bitBoundary|bitsDead != 0x11 { + gothrow("markspan: bad bits") + } + if n%(wordsPerBitmapByte*ptrSize) != 0 { + gothrow("markspan: unaligned length") + } + b = b - n/wordsPerBitmapByte + 1 // find first byte + if b%ptrSize != 0 { + gothrow("markspan: unaligned pointer") + } + for i := uintptr(0); i < n; i, b = i+wordsPerBitmapByte*ptrSize, b+ptrSize { + *(*uintptr)(unsafe.Pointer(b)) = uintptrMask & 0x1111111111111111 // bitBoundary | bitsDead, repeated + } + return + } + + if leftover { + n++ // mark a boundary just past end of last block too + } + step := size / (ptrSize * wordsPerBitmapByte) + for i := uintptr(0); i < n; i, b = i+1, b-step { + *(*byte)(unsafe.Pointer(b)) = bitBoundary | bitsDead<<2 + } +} + +// unmark the span of memory at v of length n bytes. +func unmarkspan(v, n uintptr) { + if v+n > mheap_.arena_used || v < mheap_.arena_start { + gothrow("markspan: bad pointer") + } + + off := (v - mheap_.arena_start) / ptrSize // word offset + if off%(ptrSize*wordsPerBitmapByte) != 0 { + gothrow("markspan: unaligned pointer") + } + + b := mheap_.arena_start - off/wordsPerBitmapByte - 1 + n /= ptrSize + if n%(ptrSize*wordsPerBitmapByte) != 0 { + gothrow("unmarkspan: unaligned length") + } + + // Okay to use non-atomic ops here, because we control + // the entire span, and each bitmap word has bits for only + // one span, so no other goroutines are changing these + // bitmap words. + n /= wordsPerBitmapByte + memclr(unsafe.Pointer(b-n+1), n) +} + +func mHeap_MapBits(h *mheap) { + // Caller has added extra mappings to the arena. + // Add extra mappings of bitmap words as needed. + // We allocate extra bitmap pieces in chunks of bitmapChunk. + const bitmapChunk = 8192 + + n := (h.arena_used - h.arena_start) / (ptrSize * wordsPerBitmapByte) + n = round(n, bitmapChunk) + n = round(n, _PhysPageSize) + if h.bitmap_mapped >= n { + return + } + + sysMap(unsafe.Pointer(h.arena_start-n), n-h.bitmap_mapped, h.arena_reserved, &memstats.gc_sys) + h.bitmap_mapped = n +} + +func getgcmaskcb(frame *stkframe, ctxt unsafe.Pointer) bool { + target := (*stkframe)(ctxt) + if frame.sp <= target.sp && target.sp < frame.varp { + *target = *frame + return false + } + return true +} + +// Returns GC type info for object p for testing. +func getgcmask(p unsafe.Pointer, t *_type, mask **byte, len *uintptr) { + *mask = nil + *len = 0 + + // data + if uintptr(unsafe.Pointer(&data)) <= uintptr(p) && uintptr(p) < uintptr(unsafe.Pointer(&edata)) { + n := (*ptrtype)(unsafe.Pointer(t)).elem.size + *len = n / ptrSize + *mask = &make([]byte, *len)[0] + for i := uintptr(0); i < n; i += ptrSize { + off := (uintptr(p) + i - uintptr(unsafe.Pointer(&data))) / ptrSize + bits := (*(*byte)(add(unsafe.Pointer(gcdatamask.bytedata), off/pointersPerByte)) >> ((off % pointersPerByte) * bitsPerPointer)) & bitsMask + *(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits + } + return + } + + // bss + if uintptr(unsafe.Pointer(&bss)) <= uintptr(p) && uintptr(p) < uintptr(unsafe.Pointer(&ebss)) { + n := (*ptrtype)(unsafe.Pointer(t)).elem.size + *len = n / ptrSize + *mask = &make([]byte, *len)[0] + for i := uintptr(0); i < n; i += ptrSize { + off := (uintptr(p) + i - uintptr(unsafe.Pointer(&bss))) / ptrSize + bits := (*(*byte)(add(unsafe.Pointer(gcbssmask.bytedata), off/pointersPerByte)) >> ((off % pointersPerByte) * bitsPerPointer)) & bitsMask + *(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits + } + return + } + + // heap + var n uintptr + var base uintptr + if mlookup(uintptr(p), &base, &n, nil) != 0 { + *len = n / ptrSize + *mask = &make([]byte, *len)[0] + for i := uintptr(0); i < n; i += ptrSize { + off := (uintptr(base) + i - mheap_.arena_start) / ptrSize + b := mheap_.arena_start - off/wordsPerBitmapByte - 1 + shift := (off % wordsPerBitmapByte) * gcBits + bits := (*(*byte)(unsafe.Pointer(b)) >> (shift + 2)) & bitsMask + *(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits + } + return + } + + // stack + var frame stkframe + frame.sp = uintptr(p) + _g_ := getg() + gentraceback(_g_.m.curg.sched.pc, _g_.m.curg.sched.sp, 0, _g_.m.curg, 0, nil, 1000, getgcmaskcb, noescape(unsafe.Pointer(&frame)), 0) + if frame.fn != nil { + f := frame.fn + targetpc := frame.continpc + if targetpc == 0 { + return + } + if targetpc != f.entry { + targetpc-- + } + pcdata := pcdatavalue(f, _PCDATA_StackMapIndex, targetpc) + if pcdata == -1 { + return + } + stkmap := (*stackmap)(funcdata(f, _FUNCDATA_LocalsPointerMaps)) + if stkmap == nil || stkmap.n <= 0 { + return + } + bv := stackmapdata(stkmap, pcdata) + size := uintptr(bv.n) / bitsPerPointer * ptrSize + n := (*ptrtype)(unsafe.Pointer(t)).elem.size + *len = n / ptrSize + *mask = &make([]byte, *len)[0] + for i := uintptr(0); i < n; i += ptrSize { + off := (uintptr(p) + i - frame.varp + size) / ptrSize + bits := ((*(*byte)(add(unsafe.Pointer(bv.bytedata), off*bitsPerPointer/8))) >> ((off * bitsPerPointer) % 8)) & bitsMask + *(*byte)(add(unsafe.Pointer(*mask), i/ptrSize)) = bits + } + } +} + +func unixnanotime() int64 { + var now int64 + gc_unixnanotime(&now) + return now +} |