Technical Reference Manual - InduSoft

Introduction
The following figure illustrates how IWS executes a generic thread (such as the Viewer).
Where:
Executing a Generic Thread
• Signal 1 is the Period time period (set to 50ms for this example).
• Signal 2 shows when the thread is active for the operating system.
• Signal 3 is the TimeSlice time period (set to 30ms for this example).
• Signal 4 shows the execution of the thread itself.
In this example, IWS generates a Period message every 50ms (signal 1). When IWS generates this message,
its thread becomes active and remains active until the specified TimeSlice time period (from IWS) expires. The
thread then remains inactive until IWS generates the next Period message (signal 1).
While the thread is active, the operating system is responsible for executing that thread. However, just
because a thread is active does not mean the operating system will execute it immediately — the operating
system may be executing other threads, for example.
When the operating system executes the thread, the TimeSlice timer starts counting and the thread is
executed for 20ms (TimeSlice from the operating system). After the 20ms period, the operating system
automatically switches to the next active thread (such as the Driver), and so on.
In the above example, the TimeSlice time was set to 30ms, which means the operating system is not supposed
to execute the thread more than once in each TimeSlice of IWS. However, if you specify higher values for the
IWS TimeSlice time period, it is likely that the operating system will execute the same thread more than once
in the same TimeSlice time period.
In the next example, the Period and the TimeSlice values were changed as follows, but the default operating
system TimeSlice period (20 ms) was not changed.
Setting a Higher TimeSlice
Where:
• Signal 1 is the Period time period (set to 100ms).
• Signal 2 shows when the thread is active for the operating system.
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