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#pragma once
#include <IO/ISchedulerNode.h>
namespace DB
{
/*
* Constraint defined on the set of requests in consumption state.
* It allows to track two events:
* - dequeueRequest(): resource consumption begins
* - finishRequest(): resource consumption finishes
* This allows to keep track of in-flight requests and implement different constraints (e.g. in-flight limit).
* When constraint is violated, node must be deactivated by dequeueRequest() returning `false`.
* When constraint is again satisfied, scheduleActivation() is called from finishRequest().
*
* Derived class behaviour requirements:
* - dequeueRequest() must fill `request->constraint` iff it is nullptr;
* - finishRequest() must be recursive: call to `parent_constraint->finishRequest()`.
*/
class ISchedulerConstraint : public ISchedulerNode
{
public:
ISchedulerConstraint(EventQueue * event_queue_, const Poco::Util::AbstractConfiguration & config = emptyConfig(), const String & config_prefix = {})
: ISchedulerNode(event_queue_, config, config_prefix)
{}
/// Resource consumption by `request` is finished.
/// Should be called outside of scheduling subsystem, implementation must be thread-safe.
virtual void finishRequest(ResourceRequest * request) = 0;
void setParent(ISchedulerNode * parent_) override
{
ISchedulerNode::setParent(parent_);
// Assign `parent_constraint` to the nearest parent derived from ISchedulerConstraint
for (ISchedulerNode * node = parent_; node != nullptr; node = node->parent)
{
if (auto * constraint = dynamic_cast<ISchedulerConstraint *>(node))
{
parent_constraint = constraint;
break;
}
}
}
protected:
// Reference to nearest parent that is also derived from ISchedulerConstraint.
// Request can traverse through multiple constraints while being dequeue from hierarchy,
// while finishing request should traverse the same chain in reverse order.
// NOTE: it must be immutable after initialization, because it is accessed in not thread-safe way from finishRequest()
ISchedulerConstraint * parent_constraint = nullptr;
};
}
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