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Operating Systems

Operating Systems. Lesson 12. Plan. Interrupts Windows and Interrupts Structural Exception Handling Exception Handling types __try/__except Sample: DivPtr. Interrupts. An event need an attention Hardware event (pressed keyboard key)

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Operating Systems

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  1. Operating Systems Lesson 12

  2. Plan • Interrupts • Windows and Interrupts • Structural Exception Handling • Exception Handling types • __try/__except • Sample: DivPtr

  3. Interrupts • An event need an attention • Hardware event (pressed keyboard key) • Errors (division by zero) caused by specific CPU command • Timer (Check for context switch) • Software (not valid parameters to critical call) • Interrupt Handler • A routine to take care of interrupts • Address in interrupt dispatch table according to interrupt number • CPU save current state before invoking interrupt handler

  4. Windows and Interrupts • Interrupt is very low level concept =>not directly exposed by user mode API’s • Hardware and Timer interrupts are supported through win32 synchronization objects (e.g. event) or Asynchronous Procedure Calls (APC) • Error handling interrupts are supported by Windows through Structural Exception Handling (SEH) mechanism.

  5. Structural Exception Handling • An exception is an event that occurs during the execution of a program, and requires the execution of code outside the normal flow of control • Most of the exceptions are handled by debugger (check Debug/Exceptions menu of Visual Studio)

  6. Exception Handling Types • Frame-based exception handling • Handle exceptions in particular code segment(‘frame”) • Vectored exception handling • Handles exceptions anywhere in applications • Windows: Frame-based exception handling implemented as C/C++ extension (new keywords)

  7. __try/_except __try { // guarded body of code } __except (filter-expression) { // exception-handler block } Filter expression: Execute __except block Execute next command after erroneous Search for other exception handler

  8. Sample: DivPtr with exception handlers

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