This variable helps to determine how frequently the program's threads switch
control. After a thread performs the value of DISPLAY_SWITCH_PERIOD display operations, the runtime switches control to another thread (if
one exists). Note that because a single DISPLAY statement can compile into
multiple "display operations," and because thread switching is also affected by
other program operations (such as file I/O), it is impossible to predict or
control when a thread will change control based on the presence of DISPLAY
statements in the source.
By setting DISPLAY_SWITCH_PERIOD to lower values, windows that are updated by multiple threads
update more uniformly, but more time is spent in the thread switching code.
Setting DISPLAY_SWITCH_PERIOD to higher values decreases the switching overhead,
but also causes the windows to update in blocks. In most cases, applications
that use threads run well with the default setting of "5".