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Thread execution in nanoFramework

About this document

This document describes how thread execution works with the .NET nanoFramework CLR.

Introduction to Threads

Oversimplifying it a .NET nanoFramework thread is (in terms of execution) basically a stream of IL instructions that are translated by the interpreter making things happen. This execution occurs in a cooperative fashion, meaning that a thread is allowed to run for a certain amount of time, after that it stops and the execution is passed to the next thread that meets the required conditions to run.

Thread execution

The .NET nanoFramework CLR and interpreter run on a RTOS thread. When the RTOS works in a cooperative fashion (opposed to a preemptive fashion) the thread is expected to relinquish control to the RTOS so that context switching can occur and the next RTOS thread is given the opportunity to run. This context switching in .NET nanoFramework is expected to occur after each time slot that a .NET nanoFramework thread is allowed to run. It's up to the target board developer to provide the correct way to relinquish the control of the threads execution according to the RTOS running beneath. This may not be required by all RTOS's. For example when by default the RTOS works in a preemptive fashion, the thread execution occurs in a round robin fashion among the various RTOS threads.

The execution relinquish to the underlying RTOS, so that the 'next' RTOS thread and other RTOS services can run is performed inside the Events_WaitForEvents function that is implemented for each target platform. For the current version of .NET nanoFramework this is accomplished in the following ways:

  • For targets running with ChibiOS (a CMSIS compliant RTOS) a call to osDelay(10) is sufficient and allows the kernel to run all the other threads with the same (or higher) priority.
  • For the ESP32 target - which is running with FreeRTOS - a call to vTaskDelay(0) is sufficient and allows the kernel to run all the other threads with the same (or higher) priority.