c# Object synchronisation error is thrown when calling Monitor.Pulse()

Question

I'm trying to sync between two threads in my GUI system.

The main task of the system initialising two synchronisation objects and running two threads:

private FetcherAPI fetcherAPI { get; set; }
private FileReader fileReader { get; set; }
private object readerLocker;
private object writerLocker;

public Form1() {
    InitializeComponent();
    this.fetcherAPI = new FetcherAPI();
    this.fileReader = new FileReader();

    readerLocker = new object();
    writerLocker = new object();

    new Thread(() => {
        this.fileReader.run(readerLocker);
    });

    new Thread(() => {
        this.fixerAPI.run(writerLocker, readerLocker);
    });
}

private void button1_Click(object sender, EventArgs e) {
    Monitor.Pulse(writerLocker);
}

Reader Thread:

public void run(object readerLocker) {
    while(true) {
        Monitor.Wait(readerLocker);
        readDataFromFileAndPresent();
    }
}

Writer Thread:

public void run(object writerLocker, object readerLocker) {
    while(true) {
        Monitor.Wait(writerLocker);
        fetchCurrency();
        Monitor.Pulse(readerLocker);
        Monitor.Wait(readerLocker);   
    }
}

When pressing the button I'm getting the following error:

object synchronization method was called from an unsynchronized block of code

What am I doing wrong?

it seems to me that the pulse and wait calls have to be inside a `lock` statement — Mong Zhu, Aug 27 '19 at 16:45
either [this answer](https://stackoverflow.com/a/20386028/5174469) or [this one](https://stackoverflow.com/a/3797900/5174469) or even [this one](https://stackoverflow.com/a/3798033/5174469) should answer your question — Mong Zhu, Aug 27 '19 at 16:48

score 2 · Accepted Answer · answered Aug 27 '19 at 16:47

Both Wait and Pulse can only be called if you already have the lock, i.e. you're inside a lock statement, or you've successfully used Monitor.Enter to acquire the lock. You haven't done either of those things, so : indeed, it won't work. The simplest fix would be to add a lock(writerLocker).

c# Object synchronisation error is thrown when calling Monitor.Pulse()

1 Answers1