Just to round things out for anonymous readers...
On the cRIO, as LabVIEW sets up all these independent tasks and passes them to the VxWorks operating system, each task gets scheduled for execution based on an assigned priority. LabVIEW allows a fixed enumerated set of priorities, however, VxWorks task priorities are 0-255. "normal priority" is the default for our team code in the LabVIEW framework, but that can be changed on a vi basis if you know what you are doing (don't do this at home!
).
Remember too that LabVIEW tasks are not the only things being scheduled for attention by the CPU. There are standard OS functions, a mixture of high and low priority tasks, that also need their time.
Once a task has been started it can execute to completion if it is very short or if the CPU has nothing else to schedule (rare). More often a long task is assigned a fixed slice of time on the CPU, then rotates out to give another task it's share of CPU time, then rotates back in later to get a little more done. That's why multiple tasks appear to the casual observer to run simultaneously, and why we say it's easier to think of them as happening simultaneously. Their execution is actually interleaved with fellow tasks.
This gets complicated by interruptions from higher priority tasks, and lower priority tasks are not completely starved by higher priority tasks. Usually, part of the scheduling algorithm includes how long a low priority task has been shutout of the CPU. If the CPU is full up with non-stop high priority tasks, a low priority task that has been waiting and waiting will eventually be allotted some time-essentially by having it's priority temporarily increased for a short time. There are also cases where a low priority task will lock an important system resource that a higher priority task is next in line for. In that case the low priority task will get it's priority temporarily bumped up to match the high priority task until the system resource is released, then it goes back to lowly priority status.
On multi-core processors (not the cRIO) the tasks get further scheduled across the multiple processors available.