Question

I’m developing an iOS 5 and above with latest SDK.

I have to implement a synchronized method with a Thread Lock in Objective C.

This is the Java version of what I have to do:

public abstract class MyClass 
{
    [ ... ]

    private static Object dataLock = new Object();

    public static long dataId = 0;

    [ ... ]

    public static void PostData(byte[] data)
    {
        synchronized (MyClass.getDataLock())
        {
            dataId++;
            MyClass.getDataLock().notify();
        }
    }

    public static byte[] GetData()
    {
        synchronized (MyClass.getDataLock())
        {
            try
            {
                MyClass.getDataLock().wait();
            }
            catch (InterruptedException ex)
            {}

            return MyClass.getData();
        }
    }

    [ ... ]
}

How do I implement dataLock in Objective C? As a NSObject?
How can I do PostData and GetData methods in Objective C?

Answer 1

Use the NSCondition class. E.g.:

static NSCondition* g_dataLock = nil;

...

+ (void)initialize
{
    if (self == [MyClass class])
    {
        g_dataLock = [NSCondition new];
    }
}

+ (void)postData:(NSData*)data
{
    [g_dataLock lock];
    dataId++;
    [g_dataLock signal];
    [g_dataLock unlock];
}

+ (NSData*)getData
{
    NSData* data = nil;

    [g_dataLock lock];
    [g_dataLock wait];

    data = ...

    [g_dataLock unlock];

    return data;
}

See the Thread Programming Guide for more info.