Due to a slightly different thread scheduling, tests assertions were
sometimes violated.

When the test thread has increased the timestamp too early, the monitor
thread computes a sleep duration of 1 millisecond to grab the next stack
trace sample. Because this is smaller than the sample interval of 66
milliseconds specified in the test class, the monitor thread counts this
as starvation and resets the current event and its recorded stack
samples, which is not intended in the test case.

A new introduced class helps with the coordination between the test
thread and the monitor thread and reduces the use of explicit
synchronization in the test class.