File: /usr/iports/go14/src/runtime/malloc.go
// Copyright 2014 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.
package runtime
import (
"unsafe"
)
const (
debugMalloc = false
flagNoScan = _FlagNoScan
flagNoZero = _FlagNoZero
maxTinySize = _TinySize
tinySizeClass = _TinySizeClass
maxSmallSize = _MaxSmallSize
pageShift = _PageShift
pageSize = _PageSize
pageMask = _PageMask
bitsPerPointer = _BitsPerPointer
bitsMask = _BitsMask
pointersPerByte = _PointersPerByte
maxGCMask = _MaxGCMask
bitsDead = _BitsDead
bitsPointer = _BitsPointer
mSpanInUse = _MSpanInUse
concurrentSweep = _ConcurrentSweep != 0
)
// Page number (address>>pageShift)
type pageID uintptr
// base address for all 0-byte allocations
var zerobase uintptr
// Allocate an object of size bytes.
// Small objects are allocated from the per-P cache's free lists.
// Large objects (> 32 kB) are allocated straight from the heap.
func mallocgc(size uintptr, typ *_type, flags uint32) unsafe.Pointer {
if size == 0 {
return unsafe.Pointer(&zerobase)
}
size0 := size
if flags&flagNoScan == 0 && typ == nil {
gothrow("malloc missing type")
}
// This function must be atomic wrt GC, but for performance reasons
// we don't acquirem/releasem on fast path. The code below does not have
// split stack checks, so it can't be preempted by GC.
// Functions like roundup/add are inlined. And onM/racemalloc are nosplit.
// If debugMalloc = true, these assumptions are checked below.
if debugMalloc {
mp := acquirem()
if mp.mallocing != 0 {
gothrow("malloc deadlock")
}
mp.mallocing = 1
if mp.curg != nil {
mp.curg.stackguard0 = ^uintptr(0xfff) | 0xbad
}
}
c := gomcache()
var s *mspan
var x unsafe.Pointer
if size <= maxSmallSize {
if flags&flagNoScan != 0 && size < maxTinySize {
// Tiny allocator.
//
// Tiny allocator combines several tiny allocation requests
// into a single memory block. The resulting memory block
// is freed when all subobjects are unreachable. The subobjects
// must be FlagNoScan (don't have pointers), this ensures that
// the amount of potentially wasted memory is bounded.
//
// Size of the memory block used for combining (maxTinySize) is tunable.
// Current setting is 16 bytes, which relates to 2x worst case memory
// wastage (when all but one subobjects are unreachable).
// 8 bytes would result in no wastage at all, but provides less
// opportunities for combining.
// 32 bytes provides more opportunities for combining,
// but can lead to 4x worst case wastage.
// The best case winning is 8x regardless of block size.
//
// Objects obtained from tiny allocator must not be freed explicitly.
// So when an object will be freed explicitly, we ensure that
// its size >= maxTinySize.
//
// SetFinalizer has a special case for objects potentially coming
// from tiny allocator, it such case it allows to set finalizers
// for an inner byte of a memory block.
//
// The main targets of tiny allocator are small strings and
// standalone escaping variables. On a json benchmark
// the allocator reduces number of allocations by ~12% and
// reduces heap size by ~20%.
tinysize := uintptr(c.tinysize)
if size <= tinysize {
tiny := unsafe.Pointer(c.tiny)
// Align tiny pointer for required (conservative) alignment.
if size&7 == 0 {
tiny = roundup(tiny, 8)
} else if size&3 == 0 {
tiny = roundup(tiny, 4)
} else if size&1 == 0 {
tiny = roundup(tiny, 2)
}
size1 := size + (uintptr(tiny) - uintptr(unsafe.Pointer(c.tiny)))
if size1 <= tinysize {
// The object fits into existing tiny block.
x = tiny
c.tiny = (*byte)(add(x, size))
c.tinysize -= uintptr(size1)
c.local_tinyallocs++
if debugMalloc {
mp := acquirem()
if mp.mallocing == 0 {
gothrow("bad malloc")
}
mp.mallocing = 0
if mp.curg != nil {
mp.curg.stackguard0 = mp.curg.stack.lo + _StackGuard
}
// Note: one releasem for the acquirem just above.
// The other for the acquirem at start of malloc.
releasem(mp)
releasem(mp)
}
return x
}
}
// Allocate a new maxTinySize block.
s = c.alloc[tinySizeClass]
v := s.freelist
if v == nil {
mp := acquirem()
mp.scalararg[0] = tinySizeClass
onM(mcacheRefill_m)
releasem(mp)
s = c.alloc[tinySizeClass]
v = s.freelist
}
s.freelist = v.next
s.ref++
//TODO: prefetch v.next
x = unsafe.Pointer(v)
(*[2]uint64)(x)[0] = 0
(*[2]uint64)(x)[1] = 0
// See if we need to replace the existing tiny block with the new one
// based on amount of remaining free space.
if maxTinySize-size > tinysize {
c.tiny = (*byte)(add(x, size))
c.tinysize = uintptr(maxTinySize - size)
}
size = maxTinySize
} else {
var sizeclass int8
if size <= 1024-8 {
sizeclass = size_to_class8[(size+7)>>3]
} else {
sizeclass = size_to_class128[(size-1024+127)>>7]
}
size = uintptr(class_to_size[sizeclass])
s = c.alloc[sizeclass]
v := s.freelist
if v == nil {
mp := acquirem()
mp.scalararg[0] = uintptr(sizeclass)
onM(mcacheRefill_m)
releasem(mp)
s = c.alloc[sizeclass]
v = s.freelist
}
s.freelist = v.next
s.ref++
//TODO: prefetch
x = unsafe.Pointer(v)
if flags&flagNoZero == 0 {
v.next = nil
if size > 2*ptrSize && ((*[2]uintptr)(x))[1] != 0 {
memclr(unsafe.Pointer(v), size)
}
}
}
c.local_cachealloc += intptr(size)
} else {
mp := acquirem()
mp.scalararg[0] = uintptr(size)
mp.scalararg[1] = uintptr(flags)
onM(largeAlloc_m)
s = (*mspan)(mp.ptrarg[0])
mp.ptrarg[0] = nil
releasem(mp)
x = unsafe.Pointer(uintptr(s.start << pageShift))
size = uintptr(s.elemsize)
}
if flags&flagNoScan != 0 {
// All objects are pre-marked as noscan.
goto marked
}
// If allocating a defer+arg block, now that we've picked a malloc size
// large enough to hold everything, cut the "asked for" size down to
// just the defer header, so that the GC bitmap will record the arg block
// as containing nothing at all (as if it were unused space at the end of
// a malloc block caused by size rounding).
// The defer arg areas are scanned as part of scanstack.
if typ == deferType {
size0 = unsafe.Sizeof(_defer{})
}
// From here till marked label marking the object as allocated
// and storing type info in the GC bitmap.
{
arena_start := uintptr(unsafe.Pointer(mheap_.arena_start))
off := (uintptr(x) - arena_start) / ptrSize
xbits := (*uint8)(unsafe.Pointer(arena_start - off/wordsPerBitmapByte - 1))
shift := (off % wordsPerBitmapByte) * gcBits
if debugMalloc && ((*xbits>>shift)&(bitMask|bitPtrMask)) != bitBoundary {
println("runtime: bits =", (*xbits>>shift)&(bitMask|bitPtrMask))
gothrow("bad bits in markallocated")
}
var ti, te uintptr
var ptrmask *uint8
if size == ptrSize {
// It's one word and it has pointers, it must be a pointer.
*xbits |= (bitsPointer << 2) << shift
goto marked
}
if typ.kind&kindGCProg != 0 {
nptr := (uintptr(typ.size) + ptrSize - 1) / ptrSize
masksize := nptr
if masksize%2 != 0 {
masksize *= 2 // repeated
}
masksize = masksize * pointersPerByte / 8 // 4 bits per word
masksize++ // unroll flag in the beginning
if masksize > maxGCMask && typ.gc[1] != 0 {
// If the mask is too large, unroll the program directly
// into the GC bitmap. It's 7 times slower than copying
// from the pre-unrolled mask, but saves 1/16 of type size
// memory for the mask.
mp := acquirem()
mp.ptrarg[0] = x
mp.ptrarg[1] = unsafe.Pointer(typ)
mp.scalararg[0] = uintptr(size)
mp.scalararg[1] = uintptr(size0)
onM(unrollgcproginplace_m)
releasem(mp)
goto marked
}
ptrmask = (*uint8)(unsafe.Pointer(uintptr(typ.gc[0])))
// Check whether the program is already unrolled.
if uintptr(atomicloadp(unsafe.Pointer(ptrmask)))&0xff == 0 {
mp := acquirem()
mp.ptrarg[0] = unsafe.Pointer(typ)
onM(unrollgcprog_m)
releasem(mp)
}
ptrmask = (*uint8)(add(unsafe.Pointer(ptrmask), 1)) // skip the unroll flag byte
} else {
ptrmask = (*uint8)(unsafe.Pointer(typ.gc[0])) // pointer to unrolled mask
}
if size == 2*ptrSize {
*xbits = *ptrmask | bitBoundary
goto marked
}
te = uintptr(typ.size) / ptrSize
// If the type occupies odd number of words, its mask is repeated.
if te%2 == 0 {
te /= 2
}
// Copy pointer bitmask into the bitmap.
for i := uintptr(0); i < size0; i += 2 * ptrSize {
v := *(*uint8)(add(unsafe.Pointer(ptrmask), ti))
ti++
if ti == te {
ti = 0
}
if i == 0 {
v |= bitBoundary
}
if i+ptrSize == size0 {
v &^= uint8(bitPtrMask << 4)
}
*xbits = v
xbits = (*byte)(add(unsafe.Pointer(xbits), ^uintptr(0)))
}
if size0%(2*ptrSize) == 0 && size0 < size {
// Mark the word after last object's word as bitsDead.
*xbits = bitsDead << 2
}
}
marked:
if raceenabled {
racemalloc(x, size)
}
if debugMalloc {
mp := acquirem()
if mp.mallocing == 0 {
gothrow("bad malloc")
}
mp.mallocing = 0
if mp.curg != nil {
mp.curg.stackguard0 = mp.curg.stack.lo + _StackGuard
}
// Note: one releasem for the acquirem just above.
// The other for the acquirem at start of malloc.
releasem(mp)
releasem(mp)
}
if debug.allocfreetrace != 0 {
tracealloc(x, size, typ)
}
if rate := MemProfileRate; rate > 0 {
if size < uintptr(rate) && int32(size) < c.next_sample {
c.next_sample -= int32(size)
} else {
mp := acquirem()
profilealloc(mp, x, size)
releasem(mp)
}
}
if memstats.heap_alloc >= memstats.next_gc {
gogc(0)
}
return x
}
// implementation of new builtin
func newobject(typ *_type) unsafe.Pointer {
flags := uint32(0)
if typ.kind&kindNoPointers != 0 {
flags |= flagNoScan
}
return mallocgc(uintptr(typ.size), typ, flags)
}
// implementation of make builtin for slices
func newarray(typ *_type, n uintptr) unsafe.Pointer {
flags := uint32(0)
if typ.kind&kindNoPointers != 0 {
flags |= flagNoScan
}
if int(n) < 0 || (typ.size > 0 && n > maxmem/uintptr(typ.size)) {
panic("runtime: allocation size out of range")
}
return mallocgc(uintptr(typ.size)*n, typ, flags)
}
// rawmem returns a chunk of pointerless memory. It is
// not zeroed.
func rawmem(size uintptr) unsafe.Pointer {
return mallocgc(size, nil, flagNoScan|flagNoZero)
}
// round size up to next size class
func goroundupsize(size uintptr) uintptr {
if size < maxSmallSize {
if size <= 1024-8 {
return uintptr(class_to_size[size_to_class8[(size+7)>>3]])
}
return uintptr(class_to_size[size_to_class128[(size-1024+127)>>7]])
}
if size+pageSize < size {
return size
}
return (size + pageSize - 1) &^ pageMask
}
func profilealloc(mp *m, x unsafe.Pointer, size uintptr) {
c := mp.mcache
rate := MemProfileRate
if size < uintptr(rate) {
// pick next profile time
// If you change this, also change allocmcache.
if rate > 0x3fffffff { // make 2*rate not overflow
rate = 0x3fffffff
}
next := int32(fastrand1()) % (2 * int32(rate))
// Subtract the "remainder" of the current allocation.
// Otherwise objects that are close in size to sampling rate
// will be under-sampled, because we consistently discard this remainder.
next -= (int32(size) - c.next_sample)
if next < 0 {
next = 0
}
c.next_sample = next
}
mProf_Malloc(x, size)
}
// force = 1 - do GC regardless of current heap usage
// force = 2 - go GC and eager sweep
func gogc(force int32) {
// 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 deadlocks during stoptheworld, don't bother
// trying to run gc while holding a lock. The next mallocgc without a lock
// will do the gc instead.
mp := acquirem()
if gp := getg(); gp == mp.g0 || mp.locks > 1 || !memstats.enablegc || panicking != 0 || gcpercent < 0 {
releasem(mp)
return
}
releasem(mp)
mp = nil
semacquire(&worldsema, false)
if force == 0 && memstats.heap_alloc < memstats.next_gc {
// typically threads which lost the race to grab
// worldsema exit here when gc is done.
semrelease(&worldsema)
return
}
// Ok, we're doing it! Stop everybody else
startTime := nanotime()
mp = acquirem()
mp.gcing = 1
releasem(mp)
onM(stoptheworld)
if mp != acquirem() {
gothrow("gogc: rescheduled")
}
clearpools()
// Run gc on the g0 stack. We do this so that the g stack
// we're currently running on will no longer change. Cuts
// the root set down a bit (g0 stacks are not scanned, and
// we don't need to scan gc's internal state). We also
// need to switch to g0 so we can shrink the stack.
n := 1
if debug.gctrace > 1 {
n = 2
}
for i := 0; i < n; i++ {
if i > 0 {
startTime = nanotime()
}
// switch to g0, call gc, then switch back
mp.scalararg[0] = uintptr(uint32(startTime)) // low 32 bits
mp.scalararg[1] = uintptr(startTime >> 32) // high 32 bits
if force >= 2 {
mp.scalararg[2] = 1 // eagersweep
} else {
mp.scalararg[2] = 0
}
onM(gc_m)
}
// all done
mp.gcing = 0
semrelease(&worldsema)
onM(starttheworld)
releasem(mp)
mp = nil
// now that gc is done, kick off finalizer thread if needed
if !concurrentSweep {
// give the queued finalizers, if any, a chance to run
Gosched()
}
}
// GC runs a garbage collection.
func GC() {
gogc(2)
}
// linker-provided
var noptrdata struct{}
var enoptrdata struct{}
var noptrbss struct{}
var enoptrbss struct{}
// SetFinalizer sets the finalizer associated with x to f.
// When the garbage collector finds an unreachable block
// with an associated finalizer, it clears the association and runs
// f(x) in a separate goroutine. This makes x reachable again, but
// now without an associated finalizer. Assuming that SetFinalizer
// is not called again, the next time the garbage collector sees
// that x is unreachable, it will free x.
//
// SetFinalizer(x, nil) clears any finalizer associated with x.
//
// The argument x must be a pointer to an object allocated by
// calling new or by taking the address of a composite literal.
// The argument f must be a function that takes a single argument
// to which x's type can be assigned, and can have arbitrary ignored return
// values. If either of these is not true, SetFinalizer aborts the
// program.
//
// Finalizers are run in dependency order: if A points at B, both have
// finalizers, and they are otherwise unreachable, only the finalizer
// for A runs; once A is freed, the finalizer for B can run.
// If a cyclic structure includes a block with a finalizer, that
// cycle is not guaranteed to be garbage collected and the finalizer
// is not guaranteed to run, because there is no ordering that
// respects the dependencies.
//
// The finalizer for x is scheduled to run at some arbitrary time after
// x becomes unreachable.
// There is no guarantee that finalizers will run before a program exits,
// so typically they are useful only for releasing non-memory resources
// associated with an object during a long-running program.
// For example, an os.File object could use a finalizer to close the
// associated operating system file descriptor when a program discards
// an os.File without calling Close, but it would be a mistake
// to depend on a finalizer to flush an in-memory I/O buffer such as a
// bufio.Writer, because the buffer would not be flushed at program exit.
//
// It is not guaranteed that a finalizer will run if the size of *x is
// zero bytes.
//
// It is not guaranteed that a finalizer will run for objects allocated
// in initializers for package-level variables. Such objects may be
// linker-allocated, not heap-allocated.
//
// A single goroutine runs all finalizers for a program, sequentially.
// If a finalizer must run for a long time, it should do so by starting
// a new goroutine.
func SetFinalizer(obj interface{}, finalizer interface{}) {
e := (*eface)(unsafe.Pointer(&obj))
etyp := e._type
if etyp == nil {
gothrow("runtime.SetFinalizer: first argument is nil")
}
if etyp.kind&kindMask != kindPtr {
gothrow("runtime.SetFinalizer: first argument is " + *etyp._string + ", not pointer")
}
ot := (*ptrtype)(unsafe.Pointer(etyp))
if ot.elem == nil {
gothrow("nil elem type!")
}
// find the containing object
_, base, _ := findObject(e.data)
if base == nil {
// 0-length objects are okay.
if e.data == unsafe.Pointer(&zerobase) {
return
}
// Global initializers might be linker-allocated.
// var Foo = &Object{}
// func main() {
// runtime.SetFinalizer(Foo, nil)
// }
// The relevant segments are: noptrdata, data, bss, noptrbss.
// We cannot assume they are in any order or even contiguous,
// due to external linking.
if uintptr(unsafe.Pointer(&noptrdata)) <= uintptr(e.data) && uintptr(e.data) < uintptr(unsafe.Pointer(&enoptrdata)) ||
uintptr(unsafe.Pointer(&data)) <= uintptr(e.data) && uintptr(e.data) < uintptr(unsafe.Pointer(&edata)) ||
uintptr(unsafe.Pointer(&bss)) <= uintptr(e.data) && uintptr(e.data) < uintptr(unsafe.Pointer(&ebss)) ||
uintptr(unsafe.Pointer(&noptrbss)) <= uintptr(e.data) && uintptr(e.data) < uintptr(unsafe.Pointer(&enoptrbss)) {
return
}
gothrow("runtime.SetFinalizer: pointer not in allocated block")
}
if e.data != base {
// As an implementation detail we allow to set finalizers for an inner byte
// of an object if it could come from tiny alloc (see mallocgc for details).
if ot.elem == nil || ot.elem.kind&kindNoPointers == 0 || ot.elem.size >= maxTinySize {
gothrow("runtime.SetFinalizer: pointer not at beginning of allocated block")
}
}
f := (*eface)(unsafe.Pointer(&finalizer))
ftyp := f._type
if ftyp == nil {
// switch to M stack and remove finalizer
mp := acquirem()
mp.ptrarg[0] = e.data
onM(removeFinalizer_m)
releasem(mp)
return
}
if ftyp.kind&kindMask != kindFunc {
gothrow("runtime.SetFinalizer: second argument is " + *ftyp._string + ", not a function")
}
ft := (*functype)(unsafe.Pointer(ftyp))
ins := *(*[]*_type)(unsafe.Pointer(&ft.in))
if ft.dotdotdot || len(ins) != 1 {
gothrow("runtime.SetFinalizer: cannot pass " + *etyp._string + " to finalizer " + *ftyp._string)
}
fint := ins[0]
switch {
case fint == etyp:
// ok - same type
goto okarg
case fint.kind&kindMask == kindPtr:
if (fint.x == nil || fint.x.name == nil || etyp.x == nil || etyp.x.name == nil) && (*ptrtype)(unsafe.Pointer(fint)).elem == ot.elem {
// ok - not same type, but both pointers,
// one or the other is unnamed, and same element type, so assignable.
goto okarg
}
case fint.kind&kindMask == kindInterface:
ityp := (*interfacetype)(unsafe.Pointer(fint))
if len(ityp.mhdr) == 0 {
// ok - satisfies empty interface
goto okarg
}
if _, ok := assertE2I2(ityp, obj); ok {
goto okarg
}
}
gothrow("runtime.SetFinalizer: cannot pass " + *etyp._string + " to finalizer " + *ftyp._string)
okarg:
// compute size needed for return parameters
nret := uintptr(0)
for _, t := range *(*[]*_type)(unsafe.Pointer(&ft.out)) {
nret = round(nret, uintptr(t.align)) + uintptr(t.size)
}
nret = round(nret, ptrSize)
// make sure we have a finalizer goroutine
createfing()
// switch to M stack to add finalizer record
mp := acquirem()
mp.ptrarg[0] = f.data
mp.ptrarg[1] = e.data
mp.scalararg[0] = nret
mp.ptrarg[2] = unsafe.Pointer(fint)
mp.ptrarg[3] = unsafe.Pointer(ot)
onM(setFinalizer_m)
if mp.scalararg[0] != 1 {
gothrow("runtime.SetFinalizer: finalizer already set")
}
releasem(mp)
}
// round n up to a multiple of a. a must be a power of 2.
func round(n, a uintptr) uintptr {
return (n + a - 1) &^ (a - 1)
}
// Look up pointer v in heap. Return the span containing the object,
// the start of the object, and the size of the object. If the object
// does not exist, return nil, nil, 0.
func findObject(v unsafe.Pointer) (s *mspan, x unsafe.Pointer, n uintptr) {
c := gomcache()
c.local_nlookup++
if ptrSize == 4 && c.local_nlookup >= 1<<30 {
// purge cache stats to prevent overflow
lock(&mheap_.lock)
purgecachedstats(c)
unlock(&mheap_.lock)
}
// find span
arena_start := uintptr(unsafe.Pointer(mheap_.arena_start))
arena_used := uintptr(unsafe.Pointer(mheap_.arena_used))
if uintptr(v) < arena_start || uintptr(v) >= arena_used {
return
}
p := uintptr(v) >> pageShift
q := p - arena_start>>pageShift
s = *(**mspan)(add(unsafe.Pointer(mheap_.spans), q*ptrSize))
if s == nil {
return
}
x = unsafe.Pointer(uintptr(s.start) << pageShift)
if uintptr(v) < uintptr(x) || uintptr(v) >= uintptr(unsafe.Pointer(s.limit)) || s.state != mSpanInUse {
s = nil
x = nil
return
}
n = uintptr(s.elemsize)
if s.sizeclass != 0 {
x = add(x, (uintptr(v)-uintptr(x))/n*n)
}
return
}
var fingCreate uint32
func createfing() {
// start the finalizer goroutine exactly once
if fingCreate == 0 && cas(&fingCreate, 0, 1) {
go runfinq()
}
}
// This is the goroutine that runs all of the finalizers
func runfinq() {
var (
frame unsafe.Pointer
framecap uintptr
)
for {
lock(&finlock)
fb := finq
finq = nil
if fb == nil {
gp := getg()
fing = gp
fingwait = true
gp.issystem = true
goparkunlock(&finlock, "finalizer wait")
gp.issystem = false
continue
}
unlock(&finlock)
if raceenabled {
racefingo()
}
for fb != nil {
for i := int32(0); i < fb.cnt; i++ {
f := (*finalizer)(add(unsafe.Pointer(&fb.fin), uintptr(i)*unsafe.Sizeof(finalizer{})))
framesz := unsafe.Sizeof((interface{})(nil)) + uintptr(f.nret)
if framecap < framesz {
// The frame does not contain pointers interesting for GC,
// all not yet finalized objects are stored in finq.
// If we do not mark it as FlagNoScan,
// the last finalized object is not collected.
frame = mallocgc(framesz, nil, flagNoScan)
framecap = framesz
}
if f.fint == nil {
gothrow("missing type in runfinq")
}
switch f.fint.kind & kindMask {
case kindPtr:
// direct use of pointer
*(*unsafe.Pointer)(frame) = f.arg
case kindInterface:
ityp := (*interfacetype)(unsafe.Pointer(f.fint))
// set up with empty interface
(*eface)(frame)._type = &f.ot.typ
(*eface)(frame).data = f.arg
if len(ityp.mhdr) != 0 {
// convert to interface with methods
// this conversion is guaranteed to succeed - we checked in SetFinalizer
*(*fInterface)(frame) = assertE2I(ityp, *(*interface{})(frame))
}
default:
gothrow("bad kind in runfinq")
}
reflectcall(unsafe.Pointer(f.fn), frame, uint32(framesz), uint32(framesz))
// drop finalizer queue references to finalized object
f.fn = nil
f.arg = nil
f.ot = nil
}
fb.cnt = 0
next := fb.next
lock(&finlock)
fb.next = finc
finc = fb
unlock(&finlock)
fb = next
}
}
}
var persistent struct {
lock mutex
pos unsafe.Pointer
end unsafe.Pointer
}
// Wrapper around sysAlloc that can allocate small chunks.
// There is no associated free operation.
// Intended for things like function/type/debug-related persistent data.
// If align is 0, uses default align (currently 8).
func persistentalloc(size, align uintptr, stat *uint64) unsafe.Pointer {
const (
chunk = 256 << 10
maxBlock = 64 << 10 // VM reservation granularity is 64K on windows
)
if align != 0 {
if align&(align-1) != 0 {
gothrow("persistentalloc: align is not a power of 2")
}
if align > _PageSize {
gothrow("persistentalloc: align is too large")
}
} else {
align = 8
}
if size >= maxBlock {
return sysAlloc(size, stat)
}
lock(&persistent.lock)
persistent.pos = roundup(persistent.pos, align)
if uintptr(persistent.pos)+size > uintptr(persistent.end) {
persistent.pos = sysAlloc(chunk, &memstats.other_sys)
if persistent.pos == nil {
unlock(&persistent.lock)
gothrow("runtime: cannot allocate memory")
}
persistent.end = add(persistent.pos, chunk)
}
p := persistent.pos
persistent.pos = add(persistent.pos, size)
unlock(&persistent.lock)
if stat != &memstats.other_sys {
xadd64(stat, int64(size))
xadd64(&memstats.other_sys, -int64(size))
}
return p
}