Technical Reference Manual - InduSoft

Introduction
• Signal 3 is the IWS TimeSlice time period (set to 80ms).
• Signal 4 shows the execution of the thread itself.
Notice that the thread can be executed more than once in the same TimeSlice time period. When the IWS
TimeSlice time period expires, the operating system interrupts the thread execution; however, even though the
IWS Period and TimeSlice parameters are set to 100ms and 80ms respectively, the operating system will not
execute this thread continuously for more than 20ms, because the operating system TimeSlice time period is
set to 20ms.
When the operating system is not executing the Viewer thread, the CPU can execute any other thread
or remain idle (if there are no other active threads to execute). Remember, the IWS Period and TimeSlice
parameters were created to prevent all threads from being active at the same time to prevent 100% CPU
usage.
During thread execution, the thread must handle its pending messages. For example, the Viewer module
must update any related screen objects. If there are no messages pending, the thread deactivates itself and
gives control back to the operating system. The operating system immediately switches to the next active
thread. In other words, a thread can interrupt its own execution — even if the operating system TimeSlice
time period has not yet expired (which occurs frequently in real-world applications).
Note: The Database Spy, DDE Server, LogWin, and ODBC Runtime modules do not have a
TimeSlice parameter. Consequently, after each thread handles all of its pending messages, the
threads become inactive until the next Period message for each one of the threads occurs.
The Background Task is the exception to the execution/switching process just discussed. The mechanism for
executing/switching the Background Task is described in the next section.
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