Condition Variables Manual

Table of Contents

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:

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

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() { }
{
// 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();
}

Further Reading