go/src/runtime/mwbbuf.go

const testSmallBuf …

type wbBuf …

const wbBufEntries …

const wbMaxEntriesPerCall …

// reset empties b by resetting its next and end pointers.
func (b *wbBuf) reset() { … }

// discard resets b's next pointer, but not its end pointer.
//
// This must be nosplit because it's called by wbBufFlush.
//
//go:nosplit
func (b *wbBuf) discard() { … }

// empty reports whether b contains no pointers.
func (b *wbBuf) empty() bool { … }

// getX returns space in the write barrier buffer to store X pointers.
// getX will flush the buffer if necessary. Callers should use this as:
//
//	buf := &getg().m.p.ptr().wbBuf
//	p := buf.get2()
//	p[0], p[1] = old, new
//	... actual memory write ...
//
// The caller must ensure there are no preemption points during the
// above sequence. There must be no preemption points while buf is in
// use because it is a per-P resource. There must be no preemption
// points between the buffer put and the write to memory because this
// could allow a GC phase change, which could result in missed write
// barriers.
//
// getX must be nowritebarrierrec to because write barriers here would
// corrupt the write barrier buffer. It (and everything it calls, if
// it called anything) has to be nosplit to avoid scheduling on to a
// different P and a different buffer.
//
//go:nowritebarrierrec
//go:nosplit
func (b *wbBuf) get1() *[1]uintptr { … }

//go:nowritebarrierrec
//go:nosplit
func (b *wbBuf) get2() *[2]uintptr { … }

// wbBufFlush flushes the current P's write barrier buffer to the GC
// workbufs.
//
// This must not have write barriers because it is part of the write
// barrier implementation.
//
// This and everything it calls must be nosplit because 1) the stack
// contains untyped slots from gcWriteBarrier and 2) there must not be
// a GC safe point between the write barrier test in the caller and
// flushing the buffer.
//
// TODO: A "go:nosplitrec" annotation would be perfect for this.
//
//go:nowritebarrierrec
//go:nosplit
func wbBufFlush() { … }

// wbBufFlush1 flushes p's write barrier buffer to the GC work queue.
//
// This must not have write barriers because it is part of the write
// barrier implementation, so this may lead to infinite loops or
// buffer corruption.
//
// This must be non-preemptible because it uses the P's workbuf.
//
//go:nowritebarrierrec
//go:systemstack
func wbBufFlush1(pp *p) { … }