Thread – direction or path that is taken while a program is executed

1. Below code would explain how dirty read happens when multiple thread(2 threads) tries to access Instance variable at once from two different class objects
2. Below we have 3 classes, One for Printing Report and Other for removing the report printed. Third for tracking the report status
3. The Output of the code would be Consistently 0 every time which is expected when the number of reports to be printed is in range of less than 100. However the output changes with more the no of reports to be printed. I.E. totalReportsToBePrinted = 10000000
4. This happens because for lower value of reports to be printed the thread executes fast with out context switching however for higher values other thread(RemovePrintedReports thread takes control before PrintExcelReports get completed) takes control which leads to inconsistency
5. The Same code would return 0 every time if one thread(PrintExcelReports) completes before other(RemovePrintedReports) as below when we use join and didn’t start both the threads at once.

   .
   .
           t1.start();
           t1.join();
           
           t2.start();
           t2.join();
   
   .
   .
   

PrintExcelReports.java

public class PrintExcelReports implements Runnable {
    TotalReportCount totalReportCount;

    public PrintExcelReports(TotalReportCount totalReportCount) {
        this.totalReportCount = totalReportCount;
    }

    int totalReportsToBePrinted = 1000000;

    @Override
    public void run() {
        for(int i=0;i<totalReportsToBePrinted;i++){
            totalReportCount.totalReportsCntVal -= i;
        }
    }
}

RemovePrintedReports.java

public class RemovePrintedReports implements Runnable {
    TotalReportCount totalReportCount;

    public RemovePrintedReports(TotalReportCount totalReportCount) {
        this.totalReportCount = totalReportCount;
    }

    int totalReportsToBePrinted = 1000000;

    @Override
    public void run() {
        for(int i=0;i<totalReportsToBePrinted;i++){
            totalReportCount.totalReportsCntVal -= i;
        }
    }
}

ReportCurrentStatus.java

public class ReportCurrentStatus {
    public static void main(String[] args) throws InterruptedException {
        TotalReportCount objTotalReportCount = new TotalReportCount();
        objTotalReportCount.totalReportsCntVal = 0;

        PrintExcelReports objPrinter1 = new PrintExcelReports(objTotalReportCount);
        RemovePrintedReports objPrinter2 = new RemovePrintedReports(objTotalReportCount);

        Thread t1 = new Thread(objPrinter1);
        Thread t2 = new Thread(objPrinter2);

        t1.start();
        t2.start();
        t1.join();
        t2.join();

        System.out.println(objTotalReportCount.totalReportsCntVal);
    }
}

Output when totalReportsToBePrinted is greater than 1000

RANDOM NUMBER

Output when totalReportsToBePrinted is less than 100

0