/// <summary>
/// Schedules the next enabled operation.
/// </summary>
internal void ScheduleNextEnabledOperation()
{
int?taskId = Task.CurrentId;
// TODO: figure out if this check is still needed.
// If the caller is the root task, then return.
if (taskId != null && taskId == this.Runtime.RootTaskId)
{
return;
}
AsyncOperation current = this.ScheduledOperation;
if (!this.IsRunning)
{
// TODO: check if this stop is needed.
this.Stop();
if (current.Status != AsyncOperationStatus.Completed)
{
// If scheduler is not running, throw exception to force terminate the current operation.
throw new ExecutionCanceledException();
}
}
if (current.Status != AsyncOperationStatus.Completed)
{
// Checks if concurrency not controlled by the runtime was used.
this.CheckNoExternalConcurrencyUsed();
}
// Checks if the scheduling steps bound has been reached.
this.CheckIfSchedulingStepsBoundIsReached();
if (this.Configuration.IsProgramStateHashingEnabled)
{
// Update the current operation with the hashed program state.
current.HashedProgramState = this.Runtime.GetProgramState();
}
// Get and order the operations by their id.
var ops = this.OperationMap.Values.OrderBy(op => op.Id);
// Try enable any operation that is currently waiting, but has its dependencies already satisfied.
foreach (var op in ops)
{
if (op is AsyncOperation machineOp)
{
machineOp.TryEnable();
IO.Debug.WriteLine("<ScheduleDebug> Operation '{0}' has status '{1}'.", op.Id, op.Status);
}
}
if (!this.Strategy.GetNextOperation(current, ops, out IAsyncOperation next))
{
// Checks if the program has deadlocked.
this.CheckIfProgramHasDeadlocked(ops.Select(op => op as AsyncOperation));
IO.Debug.WriteLine("<ScheduleDebug> Schedule explored.");
this.HasFullyExploredSchedule = true;
this.Stop();
if (current.Status != AsyncOperationStatus.Completed)
{
// The schedule is explored so throw exception to force terminate the current operation.
throw new ExecutionCanceledException();
}
}
this.ScheduledOperation = next as AsyncOperation;
this.ScheduleTrace.AddSchedulingChoice(next.Id);
IO.Debug.WriteLine($"<ScheduleDebug> Scheduling the next operation of '{next.Name}'.");
if (current != next)
{
current.IsActive = false;
lock (next)
{
this.ScheduledOperation.IsActive = true;
System.Threading.Monitor.PulseAll(next);
}
lock (current)
{
if (!current.IsHandlerRunning)
{
return;
}
if (!this.ControlledTaskMap.ContainsKey(Task.CurrentId.Value))
{
this.ControlledTaskMap.TryAdd(Task.CurrentId.Value, current);
IO.Debug.WriteLine("<ScheduleDebug> Operation '{0}' is associated with task '{1}'.", current.Id, Task.CurrentId);
}
while (!current.IsActive)
{
IO.Debug.WriteLine("<ScheduleDebug> Sleeping the operation of '{0}' on task '{1}'.", current.Name, Task.CurrentId);
System.Threading.Monitor.Wait(current);
IO.Debug.WriteLine("<ScheduleDebug> Waking up the operation of '{0}' on task '{1}'.", current.Name, Task.CurrentId);
}
if (current.Status != AsyncOperationStatus.Enabled)
{
throw new ExecutionCanceledException();
}
}
}
}
/// <summary>
/// Schedules the specified asynchronous operation to execute on the task with the given id.
/// </summary>
/// <param name="op">The operation to schedule.</param>
/// <param name="taskId">The id of the task to be used to execute the operation.</param>
internal void ScheduleOperation(AsyncOperation op, int taskId)
{
IO.Debug.WriteLine($"<ScheduleDebug> Scheduling operation '{op.Name}' to execute on task '{taskId}'.");
this.ControlledTaskMap.TryAdd(taskId, op);
}
/// <summary>
/// Tries to get the next enabled operation to schedule.
/// </summary>
private bool TryGetNextEnabledOperation(AsyncOperation current, bool isYielding, out AsyncOperation next)
{
// Get and order the operations by their id.
var ops = this.OperationMap.Values.OrderBy(op => op.Id);
// The scheduler might need to retry choosing a next operation in the presence of uncontrolled
// concurrency, as explained below. In this case, we implement a simple retry logic.
int retries = 0;
do
{
// Enable any blocked operation that has its dependencies already satisfied.
IO.Debug.WriteLine("<ScheduleDebug> Enabling any blocked operation with satisfied dependencies.");
foreach (var op in ops)
{
this.TryEnableOperation(op);
IO.Debug.WriteLine("<ScheduleDebug> Operation '{0}' has status '{1}'.", op.Id, op.Status);
}
// Choose the next operation to schedule, if there is one enabled.
if (!this.Strategy.GetNextOperation(ops, current, isYielding, out next) &&
this.Configuration.IsPartiallyControlledTestingEnabled &&
ops.Any(op => op.IsBlockedOnUncontrolledDependency()))
{
// At least one operation is blocked due to uncontrolled concurrency. To try defend against
// this, retry after an asynchronous delay to give some time to the dependency to complete.
Task.Run(async() =>
{
await Task.Delay(10);
lock (this.SyncObject)
{
Monitor.PulseAll(this.SyncObject);
}
});
// Pause the current operation until the scheduler retries.
Monitor.Wait(this.SyncObject);
retries++;
continue;
}
break;
}while (retries < 5);
if (next is null)
{
// Check if the execution has deadlocked.
this.Runtime.CheckIfExecutionHasDeadlocked(ops);
return(false);
}
return(true);
}