What is the java signal dispatcher thread?

Question

I was looking through a thread dump of a java process, and notice some threads blocked by signal dispatcher.

What is signal dispatcher? What does it do?

Answer 1

OS Signals are inherently single-threaded, so it's important that they are all handled on the same thread. So, a dispatcher is a natural way to achieve this. Think of it like the single GUI event thread for AWT.

On a tangential note, if you are Linux and your JVM loads a native library that inserts its own signal handlers, then you will need to preload libjsig.so. I found out the hard way when a third-party networking library intermittently tore down my connections with misdirected sigpipes.

Answer 2

I found an article about this on IBM developerWorks. When the OS raises a signal to the JVM, the signal dispatcher thread will pass the signal to the appropriate handler

Revelations on Java signal handling and termination by Chris White, Software Engineer, IBM