Question

What I would like to do is write a small program that continuously live counts the number of context switches that a specific process experiences per a sufficiently small unit of time. I have observed this functionality within the software “Process Explorer”, so I know it is definitely possible.

Unfortunately, I have very little idea of how to begin coding this and have so far been unable to find any helpful code snippets online. Thus, a small working example implementing a per process and per unit time live context switch count would be immensely helpful for me.

Answer 1

Here’s one way to do it – This will print the amount of context switches used by thread 0 of notepad (you can substitute any process and thread number you want in the CounterPathBuffer initialization) every second:

#include "stdafx.h"
#include <iostream>
#include <windows.h>
#include <stdio.h>
#include <conio.h>
#include <pdh.h>
#include <pdhmsg.h>

#pragma comment(lib, "pdh.lib")
using namespace std;
CONST ULONG SAMPLE_INTERVAL_MS    = 1000;
CONST PWSTR BROWSE_DIALOG_CAPTION = L"Select a counter to monitor.";

void wmain(void)
{
    PDH_STATUS Status;
    HQUERY Query = NULL;
    HCOUNTER Counter;
    PDH_FMT_COUNTERVALUE DisplayValue;
    DWORD CounterType;
    SYSTEMTIME SampleTime;
    PDH_BROWSE_DLG_CONFIG BrowseDlgData;
    WCHAR CounterPathBuffer[PDH_MAX_COUNTER_PATH] = L"\\\\ComputerNameGoesHere\\Thread(notepad/0)\\Context Switches/sec";


    //
    // Create a query.
    //

    Status = PdhOpenQuery(NULL, NULL, &Query);
    if (Status != ERROR_SUCCESS) 
    {
       wprintf(L"\nPdhOpenQuery failed with status 0x%x.", Status);
       goto Cleanup;
    }

    //
    // Initialize the browser dialog window settings.
    //



    ZeroMemory(&BrowseDlgData, sizeof(PDH_BROWSE_DLG_CONFIG));

    BrowseDlgData.bIncludeInstanceIndex = FALSE;
    BrowseDlgData.bSingleCounterPerAdd = TRUE;
    BrowseDlgData.bSingleCounterPerDialog = TRUE;
    BrowseDlgData.bLocalCountersOnly = FALSE;
    BrowseDlgData.bWildCardInstances = TRUE;
    BrowseDlgData.bHideDetailBox = TRUE;
    BrowseDlgData.bInitializePath = FALSE;
    BrowseDlgData.bDisableMachineSelection = FALSE;
    BrowseDlgData.bIncludeCostlyObjects = FALSE;
    BrowseDlgData.bShowObjectBrowser = FALSE;
    BrowseDlgData.hWndOwner = NULL;
    BrowseDlgData.szReturnPathBuffer = CounterPathBuffer;
    BrowseDlgData.cchReturnPathLength = PDH_MAX_COUNTER_PATH;
    BrowseDlgData.pCallBack = NULL;
    BrowseDlgData.dwCallBackArg = 0;
    BrowseDlgData.CallBackStatus = ERROR_SUCCESS;
    BrowseDlgData.dwDefaultDetailLevel = PERF_DETAIL_WIZARD;
    BrowseDlgData.szDialogBoxCaption = BROWSE_DIALOG_CAPTION;

    //
    // Add the selected counter to the query.
    //


    Status = PdhAddCounter(Query, CounterPathBuffer, 0, &Counter);
    if (Status != ERROR_SUCCESS) 
    {
        wprintf(L"\nPdhAddCounter failed with status 0x%x.", Status);
        goto Cleanup;
    }

    //
    // Most counters require two sample values to display a formatted value.
    // PDH stores the current sample value and the previously collected
    // sample value. This call retrieves the first value that will be used
    // by PdhGetFormattedCounterValue in the first iteration of the loop
    // Note that this value is lost if the counter does not require two
    // values to compute a displayable value.
    //

    Status = PdhCollectQueryData(Query);
    if (Status != ERROR_SUCCESS) 
    {
        wprintf(L"\nPdhCollectQueryData failed with 0x%x.\n", Status);
        goto Cleanup;
    }

    //
    // Print counter values until a key is pressed.
    //

    while (!_kbhit()) 
    {
        Sleep(SAMPLE_INTERVAL_MS);

        GetLocalTime(&SampleTime);

        Status = PdhCollectQueryData(Query);
        if (Status != ERROR_SUCCESS) 
        {
            wprintf(L"\nPdhCollectQueryData failed with status 0x%x.", Status);
        }

        wprintf(L"\n\"%2.2d/%2.2d/%4.4d %2.2d:%2.2d:%2.2d.%3.3d\"",
                SampleTime.wMonth,
                SampleTime.wDay,
                SampleTime.wYear,
                SampleTime.wHour,
                SampleTime.wMinute,
                SampleTime.wSecond,
                SampleTime.wMilliseconds);

        //
        // Compute a displayable value for the counter.
        //

        Status = PdhGetFormattedCounterValue(Counter,
                                             PDH_FMT_DOUBLE,
                                             &CounterType,
                                             &DisplayValue);
        if (Status != ERROR_SUCCESS) 
        {
            wprintf(L"\nPdhGetFormattedCounterValue failed with status 0x%x.", Status);
            goto Cleanup;
        }


        wprintf(L",\"%.20g\"", DisplayValue.doubleValue);
    }

Cleanup:

    //
    // Close the query.
    //

    if (Query) 
    {
       PdhCloseQuery(Query);
    }

    int x;
    cin >>x;
}

Most of the code is from this source: msdn.microsoft.com/en-us/library/aa371886%28v=vs.85%29.aspx. I would like to shorten the amount of time between consecutive checks on the context switches (make it less than a second). If anyone has any ideas as to how to do this, that’d be great.