Java调试器：进程间通信如何完成？

Question

I know that you can debug a remote JVM starting it in "debug mode" (the remote JVM opens a TCP port to communicate with the debugger).

My question is, how is this communication done when the debug is not remote but local ? for example, when you use an IDE to launch an application to debug it locally. The IDE launches the JVM in an independent process, and then how is this inter-process communication done (in the case of Windows, for example)? is it done throught a TCP port also?

Answer 1

That depends on the hosting OS. On Windows the debugger will use shared memory and there is a whole bunch of alternative ways of connecting on various OS'es: http://download.oracle.com/javase/6/docs/technotes/guides/jpda/conninv.html

In earlier versions, TCP would be quietly used unless on Windows...

The details are, however, vendor specific and the Sun VM allows you to implement your own connector, if you want to implement one that works over another protocol: http://download.oracle.com/javase/1.5.0/docs/guide/jpda/jdi/com/sun/jdi/connect/spi/TransportService.html

Answer 2

According to the JDB Docs , you can specify a transport-argument.

C:> java -agentlib:jdwp= transport=dt_shmem ,address=jdbconn,server=y,suspend=n

Under Windows , you can specify dt_shmem for communication per shared memory

From the link below:

-Xrunjdwp: transport=dt_socket ,address=myhost:8000

Under Unix/Linux (works under Win as well) the debugger and the VM communicate per Socket.

More Examples: http://download.oracle.com/javase/1.4.2/docs/guide/jpda/conninv.html

Answer 3

In general, JDWP (JavaTM Debug Wire Protocol Transport Interface) does not define the transport mechanism (socket, serial line, shared memory, ...) but the format of information and requests transferred between the debuggee process and the debugger front-end. for a particular implementation you should look at its documentation. For example, SUN VM supports two modes: TCP/IP and shared memeory.

Answer 4

For the Sun JVM, there are two modes : shared memory, and TCP/IP. You can list the options using

java -Xrunjdwp:help