[SOLVED] Reliable waiting for process tree completion

Reliable waiting for process tree completion

There is a recommendation to associate a Job Object with I/O completion port and to listen for notifications JOB_OBJECT_MSG_ACTIVE_PROCESS_ZERO as a right way to wait for child process (without access to source code) tree completion. But in MSDN:

Note that, except for limits set with the JobObjectNotificationLimitInformation information class, messages are intended only as notifications and their delivery to the completion port is not guaranteed. The failure of a message to arrive at the completion port does not necessarily mean that the event did not occur.

So there is no really reliable way to wait for the process tree completion in Windows, isn't it?

Solution

I played abit with the other options that exist and using the I/O completion port is the only available method besides WaitForObject, WaitForObjectEx and the pendant for multiple objects.

More interestingly though, at least on Windows 10, TerminateJobObject is not applied unless aforementioned methods are being called.

To that regard, QueryInformationJobObject with for example JOBOBJECT_BASIC_ACCOUNTING_INFORMATION will show that the processes in the job object are not terminated.

So to be reliable, you have to

use GetQueuedCompletionStatus with upper time limit in a loop for "expected time behavior"
on "unpexpected time behavior/too much resource usage occurs" etc, use TerminateJobObject with another call to WaitForObject, WaitForObjectEx / the multiple object pendant or the GetQueuedCompletionStatus one to ensure pending job object tasks are executed
untested, but strong suggestion: make sure to wait/get status for at least all direct ancestors of your process so that all the dependency tasks are executed
untested, but unsure: make a test for other pending job object tasks and check that the job object tasks can be executed (nothing blocking it)
to be extra sure that nothing got lost in the meantime, use afterwards QueryInformationJobObject JOBOBJECT_BASIC_ACCOUNTING_INFORMATION and the field ActiveProcesses in a loop.