java.io.IOException: The read operation timed out before any data was returned.

[felixunivers]

Hi,
I am trying your jSerialComm with Netty solution - the example and am running into this error:
"java.io.IOException: The read operation timed out before any data was returned."
It gets thrown by jSerialComm class:
private final class SerialPortInputStream extends InputStream
method:
public final int read(byte[] b, int off, int len) throws NullPointerException, IndexOutOfBoundsException, IOException
section:

// Read from the serial port
int numRead = readBytes(portHandle, b, len, off);
    if (numRead == 0)
        throw new IOException("The read operation timed out before any data was returned.");

When I use jSerialComm on its own on the same port it performs fine.

Any ideas ?

[felixunivers]

A little more detail:
on the line:
int numRead = readBytes(portHandle, b, len, off);
len = 1;
but the method returns 0 (zero) - it cannot or does not read the port data

[Ziver]

Hi,
Sorry for the very late response.

Have you tried updating the timeout, jSerialComm tend to have shorter timeouts and return without reading any data.

[georgecao]

@Ziver I see the same error message. OIO implementation use only one thread for reading or writing data. So if the device do not send any data immediately after you open the port, the entire channel will be blocked due to the autoRead option is on by default. Then you are blocked, you do NOT read anything from the input stream and you cannot write anything to the output stream b/c the only thread is blocked for reading data. Seams there is no solution to this one, beside ,OIO is deprecated by Netty too, we need a NIO implementation, right?

[georgecao]

@felixunivers find any way to fix this?

[gsrunion]

https://github.com/Fazecast/jSerialComm/wiki/Java-InputStream-and-OutputStream-Interfacing-Usage-Example

Set the read timeout to zero and the exception won't be thrown. You may also have to the use the mode of operation stated there. Netty closes the channel when an exception is thrown that is a subclass of IOException, which this SerialTimeoutException is.

[gsrunion]

Update: While my solution keeps the SerialTimeoutException from firing it is still subject to the deadlock issue @georgecao describes above. The problem with the SerialTimeoutException is that is subclasses, ultimately, IOException and when an exception is thrown that is a subclass Netty brings down the channel. Still looking for a workaround at this point.

[gsrunion]

I have a PR against JSerialComm to add an option to suppress timeout exceptions when reading from the inputstream.

Fazecast/jSerialComm@eab394d

I also made changes to my local fork of this repo to set that option. Things seem to work.

[Ziver]

Another solution if the PR on jSerialComm takes longer to merge or does not get merged would be to wrap the serial inputstream in a wrapper where we catch and ignore the SerialTimeoutException
exception.

[gsrunion]

Yes. But exceptions are generally considered expensive and the more optimum solution would be to not throw them at all.

[Ziver]

I agree, the best solution is if your PR on jSerialComm is merged.

[LisaU]

@felixunivers find any way to fix this?

Hi，NIO implementation， Is it feasible？

[gsrunion]

NIO....probably but there are few examples and even less documentation about how to implement an NIO channel. I know it comes down to implementing an interface but without a good writeup or example to worn from you have to make a lot of assumptions about what the expected behavior for the methods are.