diff options
Diffstat (limited to 'src/runtime/mgc0.h')
-rw-r--r-- | src/runtime/mgc0.h | 74 |
1 files changed, 7 insertions, 67 deletions
diff --git a/src/runtime/mgc0.h b/src/runtime/mgc0.h index 519d7206e..dd0c46024 100644 --- a/src/runtime/mgc0.h +++ b/src/runtime/mgc0.h @@ -2,81 +2,21 @@ // 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, -}; |