Bind java.lang.AutoCloseable as IDisposable

[jonpryor]

Context: dotnet/android@d3e5974

Background

Java 8 introduced a try-with-resources statement, which is conceptually similar to the C# using block:

try (BufferedReader br = new BufferedReader(new FileReader(path))) {
    String line = br.readLine();
}

The Java compiler expands this into a try-finally block:

BufferedReader br = new BufferedReader(new FileReader(path));
try {
    String line = br.readLine();
}
finally {
    if (br != null) br.close();
}

try-with-resources can be used with any type which implements java.lang.AutoCloseable.

Additionally, java.io.Closeable now implements java.lang.AutoCloseable, so all java.io constructs support try-with-resources syntax.

Binding

generator should natively support this feature: if a type implements Java.Lang.IAutoCloseable, then generation for the type should override Java.Lang.Object.Dispose(bool) to have it call Close().

For example, Java.IO.FileOutputStream implements Java.IO.ICloseable, and thus it implements Java.Lang.IAutoCloseable. generator should thus emit:

partial class FileOutputStream {
    protected override void Dispose (bool disposing)
    {
        if (disposing && PeerReference.IsValid) {
            Close ();
        }
        base.Dispose (disposing);
    }
}

By doing so, C# using blocks work as expected:

using (var f = new Java.IO.FileOutputStream("path")) {
    byte[] data = Encoding.UTF8.GetBytes("Test string...");
    stream.Write(data, 0, data.Length);
}
// f.Close() is called at end-of-block, writing data to disk

Open Questions

Do we need to worry about calling Close() multiple times? FileOutputStream inherits from OutputStream, both of which implement ICloseable. Will it be a problem when both OutputStream and FileOutputStream override Object.Dispose(bool) to call Close()?

• I believe this won't be a problem, as the Closeable.close() docs state:

  If the stream is already closed then invoking this method has no effect.