This library (Delphi 10 or higher) exposes loose equivalents of the Task and Task<T> objects in .Net that use COM infrastructure (IContextCallback.ContextCallback) to synchronize continuation calls on the main or any arbitrary thread. The same API is used by async/await in C# and co_await in VC++. The library works in both exe and dll projects and (unlike TThread.Synchornize) does not rely on periodic calls to CheckSynchronize.
The source code is licensed under the MIT license.
To use this library, add AsyncAwait to the uses clause; you can then create code like the following:
procedure TForm1.btnFibonacciClick(Sender: TObject);
var
seed: UInt64;
begin
seed := Random(MaxInt);
lblResult.Caption := Format('Calculating Fibonacci number for %d. Please wait...', [seed]);
TTask<UInt64>.Async(
//timeconsuming call on a secondary thread
function : UInt64
begin
Result := Fibonacci(seed);
end,
//update the UI on the main thread
procedure(task : ITask<UInt64>; Value : UInt64)
begin
if task.Status = TTaskStatus.RanToCompletion
then lblResult.Caption := Format('Fibonacci number for %d is %d', [seed, Value])
else if task.Status = TTaskStatus.Faulted
then lblResult.Caption := Format('Error calculating Fibonacci number: %s', [task.Exception.Message])
end,
//tell to continue on the main thread -
//don't need to specify this parameter as it defaults to true anyway
true
);
end;You can also specify a particular synchronization context even if you start a new task on a secondary thread:
procedure TForm1.Button1Click(Sender: TObject);
var
t : ITask<integer>;
syncContext : ISynchronizationContext;
begin
syncContext := TSynchronizationContext.Current;
t := TTask<integer>.Async(
//async function
function() : integer
var
delay : integer;
begin
delay := Random(10000);
sleep(delay);
Result := delay;
//run another task
//start it explicitly since we need to configure the
//synchornization context (main thread) first
//before the continuation code has a chance to run
TTask.Create(
procedure()
begin
sleep(2000);
end
).
ContinueWith(
procedure(task : ITask)
begin
ShowMessage('Done second task');
end,
//use the sync context from the main thread since we are showing a window
syncContext
).
//now start the task after we configured it
Start;
end,
//continue with
//it is guaranteed to run on the calling thread (this main thread)
//since continueOnCapturedContext parameter defaults to true
procedure(task : ITask<integer>; Value : integer )
begin
if task.Status = TTaskStatus.RanToCompletion
then ShowMessage(Format('All done after sleeping for %d seconds', [task.Value div 1000]))
else if task.Status = TTaskStatus.Faulted
then ShowMessage(Format('Task faulted. Exception type = %s: %s', [task.Exception.ClassName, task.Exception.Message]))
end,
//continue on the main thread - don't need to specify this parameter as it defaults to true
true
);
if t.Wait(2000)
then ShowMessage(Format('Done after waiting for less than 2 seconds. Task returned %d', [t.Value]))
else ShowMessage('Still not done after waiting for 2 seconds');
end;