How are the IO intensive works managed by vThreads?

[mainul35]

While executing a long poling task, during the idle time, will the vThread focus on something else and when the work is done it will come back again to the long polling task based on "continuation" principle? Or can it be a separate vThread taking on that task?

[danthe1st]

There are multiple ways this is handled.

• If possible, the continuation yields when a blocking IO operation is done. If I understood that correctly, the JVM requests the IO from the OS using some asynchronous native methods provided by the OS (e.g. telling the OS to write it in a buffer) and registers some callback (interrupt) when that is finished. Once that happens, the continuation is continued.
• If this is not possible (i.e. there is no implementation of that), the JVM temporarily increases the number of threads in the virtual thread pool to accommodate for the thread used for the I/O.
• In some cases (e.g. blocking in synchronized-blocks), the virtual thread is pinned to the platform thread, i.e. the platform thread cannot be used by other threads. This should be avoided if possible (using synchronized in virtual thread is not a problem but blocking in synchronized blocks executed in a virtual thread causes that issue).