Thanks for help, I'll try this and report back.
Igor
On Wed, Oct 24, 2012 at 1:37 AM, Jonathan Pryor <j...@xamarin.com> wrote:
> On Oct 23, 2012, at 4:32 AM, Igor Russkih <iruss...@gmail.com> wrote:
> > Assume I have my java class, and my cs class. What I want is to transfer
> binary data between these two with max performance.
> >
> > Main direction is cs -> java for now.
> >
> > What is the best way?
> >
> > 1) JNI CopyArray - how is that implemented internally? SetIntArrayRegion?
>
> Yes, JNIEnv.CopyArray is implemented atop SetIntArrayRegion() and
> SetIntArrayRegion(), plus some type overhead.
>
> > 2) DirectByteBuffer seems to be a better alternative, but on mono side,
> the only way is Marshal.ReadInt32/WriteInt32? Is that fast?
>
> This should be, as DirectByteBuffer was designed for exposure of "native"
> memory into Java processes. The only issue is that said "native" memory
> can't move, so it can't be backed by a C# byte[], but it can be backed by
> an "unmanaged" (non-moving) block of memory.
>
> As for reading the buffer contents from C#, there's Marshal.Read*() and
> Marshal.Write*(), as you note, but there is also unsafe C# code and
> pointers:
>
> void Foo(Java.Nio.Buffer buffer)
> {
> if (!buffer.IsDirect)
> throw new ArgumentException (...);
> IntPtr address = buffer.GetDirectBufferAddress();
> unsafe {
> int* p = (int*) address;
> *p = 42;
> }
> }
>
> To allocate said `buffer`, you can use either
> ByteBuffer.AllocateDirect(int) (and Java allocates the block of memory), or
> use JNIEnv.NewDirectByteBuffer() (and you allocate the memory):
>
> IntPtr directByteBuffer =
> JNIEnv.NewDirectByteBuffer(Marshal.AllocHGlobal (4096), 4096L);
> Buffer buffer =
> Java.Lang.Object.GetObject<Buffer>(directByteBuffer,
> JniHandleOwnership.TransferLocalRef);
> Foo (buffer);
>
> - Jon
>
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