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// Copyright (C) 2023 Internet Systems Consortium, Inc. ("ISC")
//
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at http://mozilla.org/MPL/2.0/.
#ifndef FLQ_ALLOCATOR_H
#define FLQ_ALLOCATOR_H
#include <dhcpsrv/allocator.h>
#include <dhcpsrv/flq_allocation_state.h>
#include <dhcpsrv/lease.h>
#include <cstdint>
namespace isc {
namespace dhcp {
/// @brief An allocator maintaining a queue of free leases.
///
/// This allocator populates the queue of free leases during the initialization.
/// It also installs the callbacks in the @c LeaseMgr, to track the subsequent
/// lease changes. It allows for maintaining the running queue of free leases.
///
/// The allocator offers the leases from the queue, minimizing the number of
/// the allocation engine's attempts to check if some other client is using
/// the offered lease. Ideally, only one check should suffice. However, when
/// several servers share a lease database, the collisions may occur because
/// the servers don't observe each others' allocations.
///
/// This allocator should only be used for reasonably small pools due to the
/// overhead to populate the free leases. A reasonably small pool is an IPv4
/// pool (including /8) and the prefix delegation pools with similar capacity.
/// This allocator is not suitable for a typical IPv6 address pool (e.g., /64).
/// An attempt to populate free leases for such a giant pool would freeze the
/// server and likely exhaust its memory.
///
/// Free leases are populated in a random order.
class FreeLeaseQueueAllocator : public Allocator {
public:
/// @brief Constructor.
///
/// @param type specifies the type of allocated leases.
/// @param subnet weak pointer to the subnet owning the allocator.
FreeLeaseQueueAllocator(Lease::Type type, const WeakSubnetPtr& subnet);
/// @brief Returns the allocator type string.
///
/// @return flq string.
virtual std::string getType() const {
return ("flq");
}
private:
/// @brief Performs allocator initialization after server's reconfiguration.
///
/// The allocator installs the callbacks in the lease manager to keep track of
/// the lease allocations and maintain the free leases queue.
virtual void initAfterConfigureInternal();
/// @brief Populates the queue of free addresses (IPv4 and IPv6).
///
/// It adds each address in the subnet pools that does not exist in the
/// list of leases to the free leases queue. The addresses are added
/// in a random order.
///
/// @param lease collection of leases in the database for a subnet.
/// @param pools collection of pools in the subnet.
/// @tparam LeaseCollectionType Type of the lease collection returned from the
/// database (i.e., @c Lease4Collection or @c Lease6Collection).
template<typename LeaseCollectionType>
void populateFreeAddressLeases(const LeaseCollectionType& leases, const PoolCollection& pools);
/// @brief Populates the queue of free delegated prefixes.
///
/// It adds each delegated prefix in the subnet pools that does not exist in the
/// list of leases to the free leases queue. The delegated prefixes are added
/// in a random order.
///
/// @param lease collection of delegated prefixes in the database for a subnet.
/// @param pools collection of prefix delegation pools in the subnet.
void populateFreePrefixDelegationLeases(const Lease6Collection& leases, const PoolCollection& pools);
/// @brief Returns next available address from the queue.
///
/// Internal thread-unsafe implementation of the @c pickAddress.
///
/// @param client_classes list of classes client belongs to.
/// @param duid client DUID (ignored).
/// @param hint client hint (ignored).
///
/// @return next offered address.
virtual asiolink::IOAddress pickAddressInternal(const ClientClasses& client_classes,
const IdentifierBaseTypePtr& duid,
const asiolink::IOAddress& hint);
/// @brief Returns next available delegated prefix from the queue.
///
/// Internal thread-unsafe implementation of the @c pickPrefix.
///
/// @param client_classes list of classes client belongs to.
/// @param pool the selected pool satisfying all required conditions.
/// @param duid Client's DUID.
/// @param prefix_length_match type which indicates the selection criteria
/// for the pools relative to the provided hint prefix length
/// @param hint Client's hint.
/// @param hint_prefix_length the hint prefix length that the client
/// provided. The 0 value means that there is no hint and that any
/// pool will suffice.
///
/// @return the next prefix.
virtual isc::asiolink::IOAddress
pickPrefixInternal(const ClientClasses& client_classes,
Pool6Ptr& pool,
const IdentifierBaseTypePtr& duid,
PrefixLenMatchType prefix_length_match,
const isc::asiolink::IOAddress& hint,
uint8_t hint_prefix_length);
/// @brief Convenience function returning pool allocation state instance.
///
/// It creates a new pool state instance and assigns it to the pool
/// if it hasn't been initialized.
///
/// @param pool pool instance.
/// @return allocation state instance for the pool.
PoolFreeLeaseQueueAllocationStatePtr getPoolState(const PoolPtr& pool) const;
/// @brief Returns a pool in the subnet the lease belongs to.
///
/// This function is used in the interface manager callbacks to find
/// a pool for a lease modified in the database.
///
/// @param lease lease instance for which the pool should be returned.
/// @return A pool found for a lease or null pointer if such a pool does
/// not exist.
PoolPtr getLeasePool(const LeasePtr& lease) const;
/// @brief Thread safe callback for adding a lease.
///
/// Removes the lease from the free lease queue.
///
/// @param lease added lease.
/// @param mt_safe a boolean flag indicating if the callback
/// has been invoked in the MT-safe context.
void addLeaseCallback(LeasePtr lease, bool mt_safe);
/// @brief Thread unsafe callback for adding a lease.
///
/// Removes the lease from the free lease queue.
///
/// @param lease added lease.
void addLeaseCallbackInternal(LeasePtr lease);
/// @brief Thread safe callback for updating a lease.
///
/// If the lease is reclaimed in this update it is added to the
/// free lease queue. If the lease is valid after the update,
/// the lease is removed from the free lease queue, if exists.
///
/// @param lease updated lease.
/// @param mt_safe a boolean flag indicating if the callback
/// has been invoked in the MT-safe context.
void updateLeaseCallback(LeasePtr lease, bool mt_safe);
/// @brief Thread unsafe callback for updating a lease.
///
/// If the lease is reclaimed in this update it is added to the
/// free lease queue. If the lease is valid after the update,
/// the lease is removed from the free lease queue, if exists.
///
/// @param lease updated lease.
void updateLeaseCallbackInternal(LeasePtr lease);
/// @brief Thread safe callback for deleting a lease.
///
/// Adds the lease to the free lease queue.
///
/// @param lease deleted lease.
/// @param mt_safe a boolean flag indicating if the callback
/// has been invoked in the MT-safe context.
void deleteLeaseCallback(LeasePtr lease, bool mt_safe);
/// @brief Thread unsafe callback for updating a lease.
///
/// Adds the lease to the free lease queue.
///
/// @param lease deleted lease.
void deleteLeaseCallbackInternal(LeasePtr lease);
/// @brief Convenience function returning a random number.
///
/// It is used internally by the @c pickAddressInternal and @c pickPrefixInternal
/// functions to select a random pool.
///
/// @param limit upper bound of the range.
/// @returns random number between 0 and limit.
uint64_t getRandomNumber(uint64_t limit);
/// @brief Random generator used by this class.
std::mt19937 generator_;
};
} // end of namespace isc::dhcp
} // end of namespace isc
#endif // FLQ_ALLOCATOR_H
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