diff options
Diffstat (limited to 'src/pkg/runtime')
| -rw-r--r-- | src/pkg/runtime/mgc0.c | 21 |
1 files changed, 16 insertions, 5 deletions
diff --git a/src/pkg/runtime/mgc0.c b/src/pkg/runtime/mgc0.c index 05b84386be..6e307bfce4 100644 --- a/src/pkg/runtime/mgc0.c +++ b/src/pkg/runtime/mgc0.c @@ -213,7 +213,7 @@ static struct { static void scanblock(byte *b, uintptr n, byte *ptrmask) { - byte *obj, *p, *arena_start, *arena_used, **wp, *scanbuf[8]; + byte *obj, *p, *arena_start, *arena_used, **wp, *scanbuf[8], bits8; uintptr i, nobj, size, idx, *bitp, bits, xbits, shift, x, off, cached, scanbufpos; intptr ncached; Workbuf *wbuf; @@ -440,16 +440,27 @@ scanblock(byte *b, uintptr n, byte *ptrmask) // Only care about not marked objects. if((bits&bitMarked) != 0) continue; - if(work.nproc == 1) - *bitp |= bitMarked<<shift; + // 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. + bits8 = xbits>>(shift&~7); + if((bits8&(bitMask|(bitMask<<gcBits))) != (bitBoundary|(bitBoundary<<gcBits))) + ((uint8*)bitp)[shift/8] = bits8 | (bitMarked<<(shift&7)); else { for(;;) { + if(runtime·casp((void**)bitp, (void*)xbits, (void*)(xbits|(bitMarked<<shift)))) + break; xbits = *bitp; bits = (xbits>>shift) & bitMask; if((bits&bitMarked) != 0) break; - if(runtime·casp((void**)bitp, (void*)xbits, (void*)(xbits|(bitMarked<<shift)))) - break; } if((bits&bitMarked) != 0) continue; |