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runtime: rename gcBits -> gcBitsArena

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This clarifies that the gcBits type is actually an arena of gcBits and
will let us introduce a new gcBits type representing a single
mark/alloc bitmap allocated from the arena.

For #19325.

Change-Id: Idedf76d202d9174a17c61bcca9d5539e042e2445
Reviewed-on: https://go-review.googlesource.com/38579
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rick Hudson <rlh@golang.org>
This commit is contained in:
Austin Clements 2017-03-24 11:36:40 -04:00
parent dc0f0ab70f
commit 9d1b2f888e
1 changed files with 12 additions and 12 deletions
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24
src/runtime/mheap.go
View file

@ -1426,24 +1426,24 @@ type gcBitsHeader struct {
} }
//go:notinheap //go:notinheap
type gcBits struct { type gcBitsArena struct {
// gcBitsHeader // side step recursive type bug (issue 14620) by including fields by hand. // gcBitsHeader // side step recursive type bug (issue 14620) by including fields by hand.
free uintptr // free is the index into bits of the next free byte; read/write atomically free uintptr // free is the index into bits of the next free byte; read/write atomically
next *gcBits next *gcBitsArena
bits [gcBitsChunkBytes - gcBitsHeaderBytes]uint8 bits [gcBitsChunkBytes - gcBitsHeaderBytes]uint8
} }
var gcBitsArenas struct { var gcBitsArenas struct {
lock mutex lock mutex
free *gcBits free *gcBitsArena
next *gcBits // Read atomically. Write atomically under lock. next *gcBitsArena // Read atomically. Write atomically under lock.
current *gcBits current *gcBitsArena
previous *gcBits previous *gcBitsArena
} }
// tryAlloc allocates from b or returns nil if b does not have enough room. // tryAlloc allocates from b or returns nil if b does not have enough room.
// This is safe to call concurrently. // This is safe to call concurrently.
func (b *gcBits) tryAlloc(bytes uintptr) *uint8 { func (b *gcBitsArena) tryAlloc(bytes uintptr) *uint8 {
if b == nil || atomic.Loaduintptr(&b.free)+bytes > uintptr(len(b.bits)) { if b == nil || atomic.Loaduintptr(&b.free)+bytes > uintptr(len(b.bits)) {
return nil return nil
} }
@ -1464,7 +1464,7 @@ func newMarkBits(nelems uintptr) *uint8 {
bytesNeeded := blocksNeeded * 8 bytesNeeded := blocksNeeded * 8
// Try directly allocating from the current head arena. // Try directly allocating from the current head arena.
head := (*gcBits)(atomic.Loadp(unsafe.Pointer(&gcBitsArenas.next))) head := (*gcBitsArena)(atomic.Loadp(unsafe.Pointer(&gcBitsArenas.next)))
if p := head.tryAlloc(bytesNeeded); p != nil { if p := head.tryAlloc(bytesNeeded); p != nil {
return p return p
} }
@ -1555,11 +1555,11 @@ func nextMarkBitArenaEpoch() {
// newArenaMayUnlock allocates and zeroes a gcBits arena. // newArenaMayUnlock allocates and zeroes a gcBits arena.
// The caller must hold gcBitsArena.lock. This may temporarily release it. // The caller must hold gcBitsArena.lock. This may temporarily release it.
func newArenaMayUnlock() *gcBits { func newArenaMayUnlock() *gcBitsArena {
var result *gcBits var result *gcBitsArena
if gcBitsArenas.free == nil { if gcBitsArenas.free == nil {
unlock(&gcBitsArenas.lock) unlock(&gcBitsArenas.lock)
result = (*gcBits)(sysAlloc(gcBitsChunkBytes, &memstats.gc_sys)) result = (*gcBitsArena)(sysAlloc(gcBitsChunkBytes, &memstats.gc_sys))
if result == nil { if result == nil {
throw("runtime: cannot allocate memory") throw("runtime: cannot allocate memory")
} }
@ -1572,7 +1572,7 @@ func newArenaMayUnlock() *gcBits {
result.next = nil result.next = nil
// If result.bits is not 8 byte aligned adjust index so // If result.bits is not 8 byte aligned adjust index so
// that &result.bits[result.free] is 8 byte aligned. // that &result.bits[result.free] is 8 byte aligned.
if uintptr(unsafe.Offsetof(gcBits{}.bits))&7 == 0 { if uintptr(unsafe.Offsetof(gcBitsArena{}.bits))&7 == 0 {
result.free = 0 result.free = 0
} else { } else {
result.free = 8 - (uintptr(unsafe.Pointer(&result.bits[0])) & 7) result.free = 8 - (uintptr(unsafe.Pointer(&result.bits[0])) & 7)