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- // Copyright (c) 2012 The Chromium Authors. All rights reserved.
- // Use of this source code is governed by a BSD-style license that can be
- // found in the LICENSE file.
- #ifndef NET_BASE_PRIORITIZED_DISPATCHER_H_
- #define NET_BASE_PRIORITIZED_DISPATCHER_H_
- #include <stddef.h>
- #include <vector>
- #include "net/base/net_export.h"
- #include "net/base/priority_queue.h"
- namespace net {
- // A priority-based dispatcher of jobs. Dispatch order is by priority (highest
- // first) and then FIFO. The dispatcher enforces limits on the number of running
- // jobs. It never revokes a job once started. The job must call OnJobFinished
- // once it finishes in order to dispatch further jobs.
- //
- // This class is NOT thread-safe which is enforced by the underlying
- // non-thread-safe PriorityQueue. All operations are O(p) time for p priority
- // levels. It is safe to execute any method, including destructor, from within
- // Job::Start.
- //
- class NET_EXPORT_PRIVATE PrioritizedDispatcher {
- public:
- class Job;
- typedef PriorityQueue<Job*>::Priority Priority;
- // Describes the limits for the number of jobs started by the dispatcher.
- // For example, |total_jobs| = 30 and |reserved_slots| = { 0, 5, 10, 5 } allow
- // for at most 30 running jobs in total. Jobs at priority 0 can't use slots
- // reserved for higher priorities, so they are limited to 10.
- // If there are already 24 jobs running, then only 6 more jobs can start. No
- // jobs at priority 1 or below can start. After one more job starts, no jobs
- // at priority 2 or below can start, since the remaining 5 slots are reserved
- // for priority 3 or above.
- struct NET_EXPORT_PRIVATE Limits {
- Limits(Priority num_priorities, size_t total_jobs);
- Limits(const Limits& other);
- ~Limits();
- // Total allowed running jobs.
- size_t total_jobs;
- // Number of slots reserved for each priority and higher.
- // Sum of |reserved_slots| must be no greater than |total_jobs|.
- std::vector<size_t> reserved_slots;
- };
- // An interface to the job dispatched by PrioritizedDispatcher. The dispatcher
- // does not own the Job but expects it to live as long as the Job is queued.
- // Use Cancel to remove Job from queue before it is dispatched. The Job can be
- // deleted after it is dispatched or canceled, or the dispatcher is destroyed.
- class Job {
- public:
- // Note: PrioritizedDispatcher will never delete a Job.
- virtual ~Job() = default;
- // Called when the dispatcher starts the job. Once the job finishes, it must
- // call OnJobFinished.
- virtual void Start() = 0;
- };
- // A handle to the enqueued job. The handle becomes invalid when the job is
- // canceled, updated, or started.
- typedef PriorityQueue<Job*>::Pointer Handle;
- // Creates a dispatcher enforcing |limits| on number of running jobs.
- explicit PrioritizedDispatcher(const Limits& limits);
- PrioritizedDispatcher(const PrioritizedDispatcher&) = delete;
- PrioritizedDispatcher& operator=(const PrioritizedDispatcher&) = delete;
- ~PrioritizedDispatcher();
- size_t num_running_jobs() const { return num_running_jobs_; }
- size_t num_queued_jobs() const { return queue_.size(); }
- size_t num_priorities() const { return max_running_jobs_.size(); }
- // Adds |job| with |priority| to the dispatcher. If limits permit, |job| is
- // started immediately. Returns handle to the job or null-handle if the job is
- // started. The dispatcher does not own |job|, but |job| must live as long as
- // it is queued in the dispatcher.
- Handle Add(Job* job, Priority priority);
- // Just like Add, except that it adds Job at the font of queue of jobs with
- // priorities of |priority|.
- Handle AddAtHead(Job* job, Priority priority);
- // Removes the job with |handle| from the queue. Invalidates |handle|.
- // Note: a Handle is valid iff the job is in the queue, i.e. has not Started.
- void Cancel(const Handle& handle);
- // Cancels and returns the oldest-lowest-priority Job invalidating any
- // handles to it. Returns NULL if the queue is empty.
- Job* EvictOldestLowest();
- // Moves the queued job with |handle| to the end of all values with priority
- // |priority| and returns the updated handle, or null-handle if it starts the
- // job. Invalidates |handle|. No-op if priority did not change.
- Handle ChangePriority(const Handle& handle, Priority priority);
- // Notifies the dispatcher that a running job has finished. Could start a job.
- void OnJobFinished();
- // Retrieves the Limits that |this| is currently using. This may not exactly
- // match the Limits this was created with. In particular, the number of slots
- // reserved for the lowest priority will always be 0, even if it was non-zero
- // in the Limits passed to the constructor or to SetLimits.
- Limits GetLimits() const;
- // Updates |max_running_jobs_| to match |limits|. Starts jobs if new limit
- // allows. Does not stop jobs if the new limits are lower than the old ones.
- void SetLimits(const Limits& limits);
- // Set the limits to zero for all priorities, allowing no new jobs to start.
- void SetLimitsToZero();
- private:
- // Attempts to dispatch the job with |handle| at priority |priority| (might be
- // different than |handle.priority()|. Returns true if successful. If so
- // the |handle| becomes invalid.
- bool MaybeDispatchJob(const Handle& handle, Priority priority);
- // Attempts to dispatch the next highest priority job in the queue. Returns
- // true if successful, and all handles to that job become invalid.
- bool MaybeDispatchNextJob();
- // Queue for jobs that need to wait for a spare slot.
- PriorityQueue<Job*> queue_;
- // Maximum total number of running jobs allowed after a job at a particular
- // priority is started. If a greater or equal number of jobs are running, then
- // another job cannot be started.
- std::vector<size_t> max_running_jobs_;
- // Total number of running jobs.
- size_t num_running_jobs_ = 0;
- };
- } // namespace net
- #endif // NET_BASE_PRIORITIZED_DISPATCHER_H_
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