// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-// Garbage collector (GC)
+// Used by cmd/gc.
enum {
- // Four bits per word (see #defines below).
gcBits = 4,
- wordsPerBitmapByte = 8/gcBits,
-
- // GC type info programs.
- // The programs allow to store type info required for GC in a compact form.
- // Most importantly arrays take O(1) space instead of O(n).
- // The program grammar is:
- //
- // Program = {Block} "insEnd"
- // Block = Data | Array
- // Data = "insData" DataSize DataBlock
- // DataSize = int // size of the DataBlock in bit pairs, 1 byte
- // DataBlock = binary // dense GC mask (2 bits per word) of size ]DataSize/4[ bytes
- // Array = "insArray" ArrayLen Block "insArrayEnd"
- // ArrayLen = int // length of the array, 8 bytes (4 bytes for 32-bit arch)
- //
- // Each instruction (insData, insArray, etc) is 1 byte.
- // For example, for type struct { x []byte; y [20]struct{ z int; w *byte }; }
- // the program looks as:
- //
- // insData 3 (BitsMultiWord BitsSlice BitsScalar)
- // insArray 20 insData 2 (BitsScalar BitsPointer) insArrayEnd insEnd
- //
- // Total size of the program is 17 bytes (13 bytes on 32-bits).
- // The corresponding GC mask would take 43 bytes (it would be repeated
- // because the type has odd number of words).
+ BitsPerPointer = 2,
+ BitsDead = 0,
+ BitsScalar = 1,
+ BitsPointer = 2,
+ BitsMask = 3,
+ PointersPerByte = 8/BitsPerPointer,
insData = 1,
insArray,
insArrayEnd,
insEnd,
- // Pointer map
- BitsPerPointer = 2,
- BitsMask = (1<<BitsPerPointer)-1,
- PointersPerByte = 8/BitsPerPointer,
-
- // If you change these, also change scanblock.
- // scanblock does "if(bits == BitsScalar || bits == BitsDead)" as "if(bits <= BitsScalar)".
- BitsDead = 0,
- BitsScalar = 1, // 01
- BitsPointer = 2, // 10
- BitsCheckMarkXor = 1, // 10
- BitsScalarMarked = BitsScalar ^ BitsCheckMarkXor, // 00
- BitsPointerMarked = BitsPointer ^ BitsCheckMarkXor, // 11
-
- BitsMultiWord = 3,
- // BitsMultiWord will be set for the first word of a multi-word item.
- // When it is set, one of the following will be set for the second word.
- // NOT USED ANYMORE: BitsString = 0,
- // NOT USED ANYMORE: BitsSlice = 1,
- BitsIface = 2,
- BitsEface = 3,
-
// 64 bytes cover objects of size 1024/512 on 64/32 bits, respectively.
MaxGCMask = 65536, // TODO(rsc): change back to 64
};
-
-// Bits in per-word bitmap.
-// #defines because we shift the values beyond 32 bits.
-//
-// Each word in the bitmap describes wordsPerBitmapWord words
-// of heap memory. There are 4 bitmap bits dedicated to each heap word,
-// so on a 64-bit system there is one bitmap word per 16 heap words.
-//
-// The bitmap starts at mheap.arena_start and extends *backward* from
-// there. On a 64-bit system the off'th word in the arena is tracked by
-// the off/16+1'th word before mheap.arena_start. (On a 32-bit system,
-// the only difference is that the divisor is 8.)
-enum {
- bitBoundary = 1, // boundary of an object
- bitMarked = 2, // marked object
- bitMask = bitBoundary | bitMarked,
- bitPtrMask = BitsMask<<2,
-};