lock and entrancy
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I ran the producer/consumer threading lock example, and set the breakpoints right after the cell locked. From my understanding, anything within a lock block should by synchronized, and only one thread can enter into a locked block at a time. However, when the program is run, the breakpoints are hit on both of the producer and consumer threads. How can this be? The code used:
// MonitorSample.cs // This example shows use of the following methods of the C# lock keyword // and the Monitor class // in threads: // Monitor.Pulse(Object) // Monitor.Wait(Object) using System; using System.Threading; public class MonitorSample { public static void Main(String[] args) { int result = 0; // Result initialized to say there is no error Cell cell = new Cell( ); CellProd prod = new CellProd(cell, 20); // Use cell for storage, // produce 20 items CellCons cons = new CellCons(cell, 20); // Use cell for storage, // consume 20 items Thread producer = new Thread(new ThreadStart(prod.ThreadRun)); Thread consumer = new Thread(new ThreadStart(cons.ThreadRun)); // Threads producer and consumer have been created, // but not started at this point. try { producer.Start( ); consumer.Start( ); producer.Join( ); // Join both threads with no timeout // Run both until done. consumer.Join( ); // threads producer and consumer have finished at this point. } catch (ThreadStateException e) { Console.WriteLine(e); // Display text of exception result = 1; // Result says there was an error } catch (ThreadInterruptedException e) { Console.WriteLine(e); // This exception means that the thread // was interrupted during a Wait result = 1; // Result says there was an error } // Even though Main returns void, this provides a return code to // the parent process. Environment.ExitCode = result; Console.WriteLine("Finished"); Console.ReadLine(); } } public class CellProd { Cell cell; // Field to hold cell object to be used int quantity = 1; // Field for how many items to produce in cell public CellProd(Cell box, int request) { cell = box; // Pass in what cell object to be used quantity = request; // Pass in how many items to produce in cell } public void ThreadRun( ) { for(int looper=1; looper<=quantity; looper++) cell.WriteToCell(looper); // "producing" } } public class CellCons { Cell cell; -
I ran the producer/consumer threading lock example, and set the breakpoints right after the cell locked. From my understanding, anything within a lock block should by synchronized, and only one thread can enter into a locked block at a time. However, when the program is run, the breakpoints are hit on both of the producer and consumer threads. How can this be? The code used:
// MonitorSample.cs // This example shows use of the following methods of the C# lock keyword // and the Monitor class // in threads: // Monitor.Pulse(Object) // Monitor.Wait(Object) using System; using System.Threading; public class MonitorSample { public static void Main(String[] args) { int result = 0; // Result initialized to say there is no error Cell cell = new Cell( ); CellProd prod = new CellProd(cell, 20); // Use cell for storage, // produce 20 items CellCons cons = new CellCons(cell, 20); // Use cell for storage, // consume 20 items Thread producer = new Thread(new ThreadStart(prod.ThreadRun)); Thread consumer = new Thread(new ThreadStart(cons.ThreadRun)); // Threads producer and consumer have been created, // but not started at this point. try { producer.Start( ); consumer.Start( ); producer.Join( ); // Join both threads with no timeout // Run both until done. consumer.Join( ); // threads producer and consumer have finished at this point. } catch (ThreadStateException e) { Console.WriteLine(e); // Display text of exception result = 1; // Result says there was an error } catch (ThreadInterruptedException e) { Console.WriteLine(e); // This exception means that the thread // was interrupted during a Wait result = 1; // Result says there was an error } // Even though Main returns void, this provides a return code to // the parent process. Environment.ExitCode = result; Console.WriteLine("Finished"); Console.ReadLine(); } } public class CellProd { Cell cell; // Field to hold cell object to be used int quantity = 1; // Field for how many items to produce in cell public CellProd(Cell box, int request) { cell = box; // Pass in what cell object to be used quantity = request; // Pass in how many items to produce in cell } public void ThreadRun( ) { for(int looper=1; looper<=quantity; looper++) cell.WriteToCell(looper); // "producing" } } public class CellCons { Cell cell;When you call Monitor.Wait() from within the lock, the lock is released and that thread waits for another thread to call Pulse. When that happens, the lock will be re-acquired and the process will continue.
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When you call Monitor.Wait() from within the lock, the lock is released and that thread waits for another thread to call Pulse. When that happens, the lock will be re-acquired and the process will continue.