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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