About

A condition variable is used to wake a waiting thread to perform some action. It is typically used together with custom threads, see Threads Manual.

Condition

A condition variable is based on maxon::ConditionVariableInterface:

maxon::ConditionVariableInterface::Wait(): Waits until the condition variable has been set or a certain amount of time has passed.
maxon::ConditionVariableInterface::Set(): Sets the condition variable to wake a thread up.
maxon::ConditionVariableInterface::Clear(): Clears the condition variable.
maxon::ConditionVariableInterface::ObservableFinished(): This observable triggered after the condition is set.

Warning: Waiting for a condition variable in a job might result in a deadlock. Consider using LazyInit or LazyInitThreaded for initialization instead.

A condition variable can have multiple dependencies. This means that Set() must be called multiple times:

maxon::ConditionVariableInterface::AddDependency(): Adds another dependency to the condition.

A condition variable is typically used as a member variable of a custom thread:

// This example shows how a thread uses a condition variable to wait for a command.
 
class ExampleThread : public maxon::ThreadInterfaceTemplate<ExampleThread>
{
public:
 ~ExampleThread() { }
 
 maxon::Result<void> Init()
 {
 iferr_scope;
 // create the condition variable
 _condition = maxon::ConditionVariableRef::Create() iferr_return;
 return maxon::OK;
 }
 
 // worker
 maxon::Result<void> operator ()()
 {
 while (!IsCancelled())
 {
 // check if condition is set, if not wait for another second
 const maxon::Seconds timeValue = maxon::Seconds(1);
 if (_condition.Wait(timeValue))
 {
 DiagnosticOutput("Action");
 
 // clear the condition variable to wait again
 _condition.Clear();
 }
 }
 
 return maxon::OK;
 }
 
 // set the condition variable to wake the thread
 void Action()
 {
 _condition.Set();
 }
 
 const maxon::Char* GetName() const { return "ExampleThread"; }
 
private:
 maxon::ConditionVariableRef _condition; 
};

This example thread can be used like this:

 // This example creates, starts and controls a thread with its condition variable.
 
 if (!g_exampleThread)
 {
 // create thread and call Init()
 g_exampleThread = ExampleThread::Create() iferr_return;
 g_exampleThread->Init() iferr_return;
 
 DiagnosticOutput("Start thread...");
 g_exampleThread.Start() iferr_return;
 }
 
 if (g_exampleThread)
 {
 // wake the thread
 g_exampleThread->Action();
 }

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