ThreadSafeSwift

Collection of Property Wrappers and other Types explicitly designed to provide quick, simple, and efficient Thread-Safety in your Swift projects.

Installation

Xcode Projects

Select File -> Swift Packages -> Add Package Dependency and enter https://github.com/Flowduino/ThreadSafeSwift.git

Swift Package Manager Projects

You can use ThreadSafeSwift as a Package Dependency in your own Packages’ Package.swift file:

let package = Package(
    //...
    dependencies: [
        .package(
            url: "https://github.com/Flowduino/ThreadSafeSwift.git",
            .upToNextMajor(from: "1.1.0")
        ),
    ],
    //...
)

From there, refer to ThreadSafeSwift as a “target dependency” in any of your package’s targets that need it.

targets: [
    .target(
        name: "YourLibrary",
        dependencies: [
          "ThreadSafeSwift",
        ],
        //...
    ),
    //...
]

You can then do import ThreadSafeSwift in any code that requires it.

Usage

Here are some quick and easy usage examples for the features provided by ThreadSafeSwift:

@ThreadSafeSemaphore - Property Wrapper

You can use the ThreadSafeSemaphore Property Wrapper to encapsulate any Value Type behind a Thread-Safe DispatchSemaphore. This is extremely easy for most types:

@ThreadSafeSemaphore var myInt: Int

Further, you can access the underlying DispatchSemaphore directly, which is useful where you need to acquire the Lock for multiple operations that must performed Atomically:

@ThreadSafeSemaphore var myInts: [Int]

//...

func incrementEveryIntegerByOne() {
    _myInts.lock.wait()
    for (index,val) in myInts.enumerated() {
        myInts[index] = val + 1
    }
    _myInts.lock.signal()
}

Of course, for Arrays, you really should try to minimize the number of get/set operations required, and the duration throughout which the DispatchSemaphore is locked:

@ThreadSafeSemaphore var myInts: [Int]

//...

func incrementEveryIntegerByOne() {
    var values = myInts // This would marshal the `DispatchSemaphore` and return a copy of the Array, then release the `DispatchSemaphore`
    for (index,val) in values.enumerated() {
        myInts[index] = val + 1
    }
    myInts = values // This would marshal the `DispatchSempahore` and replace the entire Array with our modified one, then release the `DispatchSemaphore`
}

ThreadSafeSemaphore.withLock - Execute a Closure while retaining the Lock

Often, it is necessary to perform more than one operation on a Value… and when you need to do this, you’ll want to ensure that you retain the DispatchSemaphore lock against the value for the duration of these operations. To facilitate this, we can use the withLock method against any ThreadSafeSemaphore decorated variable:

@ThreadSafeSemaphore var myInts: [Int] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] 

Here we have a ThreadSafeSemaphore decorated Array of Integers.

If we want to perform any number of operations against any number of values within this Array, we can now do so in a thread-safe manner using withLock:

func incrementEachValueByOne() {
    _myInts.withLock { value in
        for (index, val) in value.enumerated() {
            value[index] = val + 1
        }
    }
}

Please pay attention to the preceeding underscore _ before myInts when invoking the withLock method. This is important, as the underscore instructs Swift to reference the Property Decorator rather than its wrappedValue.

IMPORTANT NOTE: - You must not reference the variable itself (in the above example, myInts) within the scope of the Closure. If you do, the Thread will lock at that command and proceed no further. All mutations to the value must be performed against value as defined within the scope of the Closure itself (as shown above).

So, as you can see, we can now encapsulate complex types with the @ThreadSafeSemaphore decorator and operate against all of its members within the safety of the DispatchSemaphore lock.

ThreadSafeSemaphore.withTryLock - Execute a Closure while retaining the Lock IF we can acquire it, otherwise execute a failure Closure

As with ThreadSafeSemaphore.withLock (explained above), we may need to perform one or more operations within the context of the DispatchSemaphore only if it is possible to obtain the DispatchSemaphore Lock at that time. Where it is not possible to acquire the DispatchSemaphore lock at that moment, we may want to execute another piece of conditional code.

We can do that easily:

@ThreadSafeSemaphore var myInts: [Int] = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Again, we declare our @ThreadSafeSemaphore decorated Variable.

Now let’s see how we would use withTryLock against myInts:

func incrementEachValueByOne() {
    _myInts.withTryLock { value in
        // If we got the Lock
        for (index, val) in value.enumerated() {
            value[index] = val + 1
        }
    } _: {
        // If we couldn't get the Lock
        print("We wanted to acquire the Lock, but couldn't... so we can do something else instead!")
    }
}

IMPORTANT NOTE: - You must not reference the variable itself (in the above example, myInts) within the scope of the either Closure. If you do, the Thread will lock at that command and proceed no further. All mutations to the value must be performed against value as defined within the scope of the Closure itself (as shown above).

These Conditional Closures are extremely useful where your code needs to progress down a different execution path depending on whether it can or cannot acquire the DispatchSemaphore lock at the point of execution.

TIP: - I use this very approach to implement “Revolving Door Locks” for Collections. A feature that will be added to this library very soon!

License

ThreadSafeSwift is available under the MIT license. See the LICENSE file for more info.