Re: [Libguestfs] [PATCH libnbd 5/9] golang: aio_buffer.go: Add Slice()

On Sun, Jan 30, 2022 at 01:33:33AM +0200, Nir Soffer wrote: > AioBuffer.Bytes() cannot be used for coping images from NBD to other copying > APis because it copies the entire image. Add a new Slice() function, > creating a slice backed by the underling buffer. underlying > > Using Slice() is efficient, but less safe, like Get(). The returned > slice must be used only before calling Free(). This should not be an > issue with typical code. > > Testing show that Slice() is much faster than Bytes() for typical 256k > buffer: > > BenchmarkAioBufferBytes-12 86616 16529 ns/op > BenchmarkAioBufferSlice-12 1000000000 0.4630 ns/op > > I modified the aio_copy example to use AioBuffer and complied 2 compiled > +++ b/golang/libnbd_620_aio_buffer_test.go > @@ -44,20 +44,35 @@ func TestAioBuffer(t *testing.T) { > /* Modifying returned slice does not modify the buffer. */ > for i := 0; i < len(b); i++ { > b[i] = 42 > } > > /* Bytes() still returns zeroes. */ > if !bytes.Equal(buf.Bytes(), zeroes) { > t.Fatalf("Expected %v, got %v", zeroes, buf.Bytes()) > } > > + /* Creating a slice without copying the underlhing buffer. */ underlying > + s := buf.Slice() > + if !bytes.Equal(s, zeroes) { > + t.Fatalf("Expected %v, got %v", zeroes, s) > + } > + > + /* Modifing the slice modifies the underlying buffer. */ Modifying > } > + > +// Benchmark creating a slice without copying the underling buffer. underlying > +func BenchmarkAioBufferSlice(b *testing.B) { > + buf := MakeAioBuffer(bufferSize) > + defer buf.Free() > + var r int > + > + b.ResetTimer() > + for i := 0; i < b.N; i++ { > + r += len(buf.Slice()) > + } > +} > -- > 2.34.1