X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/2c6557f613fcf6cdcebb08c321a5d061aeb780c6..2aff408211e84a226af6f74cb9338cbaf3fc4645:/services/keepstore/streamwriterat.go

diff --git a/services/keepstore/streamwriterat.go b/services/keepstore/streamwriterat.go
index 365b55f233..02dce6e216 100644
--- a/services/keepstore/streamwriterat.go
+++ b/services/keepstore/streamwriterat.go
@@ -19,10 +19,16 @@ import (
 // streamWriterAt writes the data to the provided io.Writer in
 // sequential order.
 //
+// streamWriterAt can also be wrapped with an io.OffsetWriter to
+// provide an asynchronous buffer: the caller can use the io.Writer
+// interface to write into a memory buffer and return without waiting
+// for the wrapped writer to catch up.
+//
 // Close returns when all data has been written through.
 type streamWriterAt struct {
 	writer     io.Writer
 	buf        []byte
+	writepos   int         // target offset if Write is called
 	partsize   int         // size of each part written through to writer
 	endpos     int         // portion of buf actually used, judging by WriteAt calls so far
 	partfilled []int       // number of bytes written to each part so far
@@ -81,7 +87,7 @@ func (swa *streamWriterAt) writeToWriter() {
 	}
 }
 
-// WriteAt implements io.WriterAt.
+// WriteAt implements io.WriterAt. WriteAt is goroutine-safe.
 func (swa *streamWriterAt) WriteAt(p []byte, offset int64) (int, error) {
 	pos := int(offset)
 	n := 0