在本机方法中等待I / O完成的Java线程阻塞

Question

I have a Thread blocking in a native method, which in turn is blocking and waiting for a linux read function ( include <fcntl.h> ) to return:

int n = read(g_fd, dest, len);

where g_fd is the file descriptor of a serial port

In this situation, how to "interrupt" the blocking thread?

EDIT for someone who has the same problem:

1. Infinite blocking IO should be avoid. There is no apparent way to interrupt it

2. @Rohit Karlupia's answer should work

3. A hackish way is to share file descriptor between Java and native code, as this article demonstrated: http://www.kfu.com/~nsayer/Java/jni-filedesc.html Then we can make interruptable Java IO stream objects with the FileDescriptor

Answer 1

Not sure if this will work for you, but in a similar case (with a socket read) I resorted to closing the socket as an "interrupt". The read() call may then return. In my case it "returned" by throwing some exception which I caught and treated an an interrupt. ie

public int myRead(g_fd, dest, len) {
   try {
      return read(g_fd, dest, len);
   }
   catch (SomeIOExceptionIForgetWhatItWas ex) {
      throw new InterruptedException();
   }
}

You might also have to check for a -1 (or some other special code) as well.

Answer 2

Java supports interruptible IO, but that would work only with java IO classes and not the system calls directly invoked via native code. Java does have packages for talking to serial port. See if you could use them instead of native code.

If native code is unavoidable, then you could do something like this. - open the fd in non-blocking mode - to simulate blocking behavior, use select with the single fd you created above - instead of using infinite timeout in select, use say per second timeout with a loop - to interrupt the thread, you could set a flag from other thread, which can be checked by the "wrapper code" for read every second it comes out of the select timeout.

int myread(int fd) {
    FDSET fdset = ...;
    while (at least one byte read or error) {
       add fd to fdset 
       select(fdset) 
       if (read events) {
          do real read 
          return;
       }else {
          if (timeout) {
             check global/object level interrupt flag 
             if (set interrupt flag) {
                return;
             }
          }
       }
    }
}