“Object synchronization method was called from an unsynchronized block of code” using monitors and lock

Question

I've searched on the existing posts about this error but I not resolved my problem with what I found there.

I'm implementing the consumer-producer problem using a lock and 2 objects for monitors. But when I run the code a get the following error 'Object synchronization method was called from an unsynchronized block of code.'. I've atached my code bellow:

ProducerConsumer.cs :

using System;
using System.Collections.Generic;
using System.Threading;

namespace ProducerConsumer
{
    public class ProducerConsumer
    {
        private Queue<int> _items;
        private object _lockObject;
        private object _condProd;
        private object _condCons;

        public ProducerConsumer()
        {
            _items = new Queue<int>();
            _lockObject = new object();
            _condProd = new object();
            _condCons = new object();
        }

        public void Produce(string name)
        {
            int count = 1;
            bool produced = false;

            while (true)
            {     
                if (produced == false)
                {
                    Console.WriteLine(name + "/Produced: " + count);
                    Thread.Sleep(50);
                    produced = true;
                    count++;
                }

                lock (_lockObject)
                {
                    while (_items.Count == 5)
                    {
                        Monitor.Wait(_condProd);
                    }

                    _items.Enqueue(count);
                }
                Monitor.Pulse(_condCons);

                produced = false;

            }
        }

        public void Consume(string name)
        {
            int count = 0;
            while (true)
            {
                lock (_lockObject)
                {
                    while (_items.Count == 0)
                    {
                        Monitor.Wait(_condCons);
                    }

                    count = _items.Dequeue();
                    Console.WriteLine(name + "/Scos din lista: " + count);
                }

                Monitor.Pulse(_condProd);
            }
        }
    }
}

Program.cs :

using System;
using System.Threading.Tasks;

namespace ProducerConsumer
{
    class Program
    {
        static void Main(string[] args)
        {
            ProducerConsumer pc = new ProducerConsumer();
            Task p = Task.Factory.StartNew(() => pc.Produce("Producer 1"));
            Task c = Task.Factory.StartNew(() => pc.Consume("Consumer 1"));
            Task.WaitAll(p, c);
            Console.ReadKey();
        }
    }
}

Please help me to understand why I get this error and how I can resolve it, I'm new in the threading section of the C# language. Thank you in advance.

Answer 1

To call Monitor.Pulse(_condCons); you need to hold the lock on _condCons ; to call Monitor.Wait(_condProd); you need to hold the lock on _condProd . It isn't clear that the wait is locking on the right object, and the pulse doesn't seem to be locking on any object.