VirtualThreads.allThreads() (and JDWP VirtualMachine/AllThreads) enumerates all active platform threads, virtual threads are not enumerated.
Thread groups
Virtual threads are not active members of a thread group.
JDI ThreadGroupReference::threads (and JDWP ThreadGroupReference/Children) enumerate all active platform threads in a group, virtual threads are not enumerated.
ThreadStartRequest/ThreadDeathRequest define a new method to control whether thread start/end events are sent for all threads or only platform threads.
IsVirtual
JDI ThreadReference defines isVirtual() to test if a thread is a virtual thread.
JDWP ThreadReference/IsVirtual is the equivalent.
Not Supported
The following are not currently supported for virtual threads:
- JDI ThreadReference.stop
- JDI ThreadReference.interrupt
- JDI StackFrame.setValue
JDWP agent options
As a temporary solution to allow existing debuggers work with virtual threads, the JDWP agent will track virtual threads so they can be enumerated for debuggers that want to enumerate all virtual threads. The options that control this behaviour are:
Option Name and Value | Description | Default |
---|---|---|
enumeratevthreads=y|n | thread lists include vthreads | n |
trackvthreads=some|all | track some or all vthreads | some |
fakevthreadstartevent=y|n | send fake start event when needed | y |
- enumeratevthreads control whether or not virtual threads are included in list of threads returned by JDWP VirtualThread/AllThreads command.
- trackvthreads controls which virtual threads will be returned when enumeratevthreads=y.
- fakevthreadstartevent is independent of the two others. If y, then before sending an event, send a fake THREAD_START event for if the debugger hasn’t already been notified about the virtual thread that the event occurs on. Note currently there is a bug, and if trackvthreads=all, no fake THREAD_START will ever be sent. This is only an issue if the debug agent is started after some virtual threads have been created.
Links
Project Loom Early Access builds