436 lines
17 KiB
Racket
436 lines
17 KiB
Racket
#lang typed/syndicate/roles
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;; ---------------------------------------------------------------------------------------------------
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;; Protocol
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#|
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Conversations in the flink dataspace primarily concern two topics: presence and
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task execution.
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Presence Protocol
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-----------------
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The JobManager (JM) asserts its presence with (job-manager-alive). The operation
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of each TaskManager (TM) is contingent on the presence of a job manager.
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|#
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(assertion-struct job-manager-alive : JobManagerAlive ())
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#|
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In turn, TaskManagers advertise their presence with (task-manager ID slots),
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where ID is a unique id, and slots is a natural number. The number of slots
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dictates how many tasks the TM can take on. To reduce contention, the JM
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should only assign a task to a TM if the TM actually has the resources to
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perform a task.
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|#
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(assertion-struct task-manager : TaskManager (id slots))
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;; an ID is a symbol
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(define-type-alias ID Symbol)
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#|
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The resources available to a TM are its associated TaskRunners (TRs). TaskRunners
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assert their presence with (task-runner ID Status), where Status is one of
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- IDLE, when the TR is not executing a task
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- (executing TaskID), when the TR is executing the task with the given TaskID
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- OVERLOAD, when the TR has been asked to perform a task before it has
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finished its previous assignment. For the purposes of this model, it indicates a
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failure in the protocol; like the exchange between the JM and the TM, a TR
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should only receive tasks when it is IDLE.
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|#
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(assertion-struct task-runner : TaskRunner (id status))
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(define-constructor* (executing : Executing id))
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(define-type-alias TaskID Int)
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(define-type-alias Status (U Symbol (Executing TaskID)))
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(define IDLE : Status 'idle)
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(define OVERLOAD : Status 'overload)
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#|
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Task Delegation Protocol
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-----------------------
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Task Delegation has two roles, TaskAssigner (TA) and TaskPerformer (TP).
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A TaskAssigner asserts the association of a Task with a particular TaskPerformer
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through
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(task-assignment ID ID Task)
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where the first ID identifies the TP and the second identifies the job.
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|#
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(assertion-struct task-assignment : TaskAssignment (assignee job-id task))
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#|
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A Task is a (task TaskID Work), where Work is one of
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- (map-work String)
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- (reduce-work (U TaskID TaskResult) (U TaskID TaskResult)), referring to either the
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ID of the dependent task or its results. A reduce-work is ready to be executed
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when it has both results.
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A TaskID is a natural number
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A TaskResult is a (Hashof String Natural), counting the occurrences of words
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|#
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(define-constructor* (task : Task id desc))
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(define-constructor* (map-work : MapWork data))
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(define-constructor* (reduce-work : ReduceWork left right))
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(define-type-alias WordCount (Hash String Int))
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(define-type-alias TaskResult WordCount)
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(define-type-alias Reduce
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(ReduceWork (Either TaskID TaskResult)
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(Either TaskID TaskResult)))
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(define-type-alias Work
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(U Reduce (MapWork String)))
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(define-type-alias ConcreteWork
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(U (ReduceWork TaskResult TaskResult)
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(MapWork String)))
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(define-type-alias PendingTask
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(Task TaskID Work))
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(define-type-alias ConcreteTask
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(Task TaskID ConcreteWork))
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#|
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The TaskPerformer responds to a task-assignment by describing its state with respect
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to that task,
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(task-state ID ID ID TaskStateDesc)
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where the first ID is that of the TP, the second is that of the job,
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and the third that of the task.
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A TaskStateDesc is one of
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- ACCEPTED, when the TP has the resources to perform the task. (TODO - not sure if this is ever visible, currently)
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- OVERLOAD/ts, when the TP does not have the resources to perform the task.
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- RUNNING, indicating that the task is being performed
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- (finished TaskResult), describing the results
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|#
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(assertion-struct task-state : TaskState (assignee job-id task-id desc))
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(define-constructor* (finished : Finished data))
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(define-type-alias TaskStateDesc
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(U Symbol (Finished TaskResult)))
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(define ACCEPTED : TaskStateDesc 'accepted)
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(define RUNNING : TaskStateDesc 'running)
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;; this is gross, it's needed in part because equal? requires two of args of the same type
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(define OVERLOAD/ts : TaskStateDesc 'overload)
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#|
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Two instances of the Task Delegation Protocol take place: one between the
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JobManager and the TaskManager, and one between the TaskManager and its
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TaskRunners.
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|#
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#|
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Job Submission Protocol
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-----------------------
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Finally, Clients submit their jobs to the JobManager by asserting a Job, which is a (job ID (Listof Task)).
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The JobManager then performs the job and, when finished, asserts (job-finished ID TaskResult)
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|#
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(assertion-struct job : Job (id tasks))
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(assertion-struct job-finished : JobFinished (id data))
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(define-type-alias τc
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(U (TaskRunner ID Status)
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(TaskAssignment ID ID ConcreteTask)
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(Observe (TaskAssignment ID ★/t ★/t))
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(TaskState ID ID TaskID TaskStateDesc)
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(Observe (TaskState ID ID TaskID ★/t))
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(JobManagerAlive)
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(Observe (JobManagerAlive))
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(Observe (TaskRunner ★/t ★/t))
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(TaskManager ID Int)
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(Observe (TaskManager ★/t ★/t))
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(Job ID (List PendingTask))
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(Observe (Job ★/t ★/t))
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(JobFinished ID TaskResult)))
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;; ---------------------------------------------------------------------------------------------------
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;; Util Macros
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(require syntax/parse/define)
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(define-simple-macro (log fmt . args)
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(begin
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(printf fmt . args)
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(printf "\n")))
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;; ---------------------------------------------------------------------------------------------------
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;; TaskRunner
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(define (word-count-increment [h : WordCount]
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[word : String]
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-> WordCount)
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(hash-update/failure h
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word
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add1
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0))
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(define (count-new-words [word-count : WordCount]
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[words : (List String)]
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-> WordCount)
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(for/fold ([result word-count])
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([word words])
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(word-count-increment result word)))
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(require/typed "flink-support.rkt"
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[string->words : (→fn String (List String))])
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(define (spawn-task-runner)
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(define id (gensym 'task-runner))
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(spawn τc
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(start-facet runner
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(field [status Status IDLE])
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(define (idle?) (equal? IDLE (ref status)))
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(assert (task-runner id (ref status)))
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(begin/dataflow
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(log "task-runner ~v state is: ~a" id (ref status)))
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(during (task-assignment id
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(bind job-id ID)
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(task (bind task-id TaskID)
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(bind desc ConcreteWork)))
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(field [state TaskStateDesc ACCEPTED])
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(assert (task-state id job-id task-id (ref state)))
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(cond
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[(idle?)
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;; since we currently finish everything in one turn, these changes to status aren't
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;; actually visible.
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(set! state RUNNING)
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(set! status (executing task-id))
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(match desc
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[(map-work (bind data String))
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(define wc (count-new-words (ann (hash) WordCount) (string->words data)))
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(set! state (finished wc))]
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[(reduce-work (bind left WordCount) (bind right WordCount))
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(define wc (hash-union/combine left right +))
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(set! state (finished wc))])
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(set! status IDLE)]
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[#t
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(set! status OVERLOAD)])))))
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;; ---------------------------------------------------------------------------------------------------
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;; TaskManager
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(define (spawn-task-manager)
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(define id (gensym 'task-manager))
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(spawn τc
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(start-facet tm
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(log "Task Manager (TM) ~a is running" id)
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(during (job-manager-alive)
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(log "TM learns about JM")
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(define/query-set task-runners (task-runner (bind id ID) discard) id
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#;#:on-add #;(log "TM learns about task-runner ~a" id))
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;; I wonder just how inefficient this is
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(define/query-set idle-runners (task-runner (bind id ID) IDLE) id
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#;#:on-add #;(log "TM learns that task-runner ~a is IDLE" id)
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#;#:on-remove #;(log "TM learns that task-runner ~a is NOT IDLE" id))
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(assert (task-manager id (set-count (ref idle-runners))))
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(field [busy-runners (List ID) (list)])
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(define (can-accept?)
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(not (set-empty? (ref idle-runners))))
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(during (task-assignment id
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(bind job-id ID)
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(task (bind task-id TaskID)
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(bind desc ConcreteWork)))
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(define status0 : TaskStateDesc
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(if (can-accept?)
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RUNNING
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OVERLOAD/ts))
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(field [status TaskStateDesc status0])
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(assert (task-state id job-id task-id (ref status)))
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(when (can-accept?)
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(define runner (set-first (ref idle-runners)))
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;; n.b. modifying a query set is questionable
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;; but if we wait for the IDLE assertion to be retracted, we might assign multiple tasks to the same runner.
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;; Could use the busy-runners field to avoid that
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(set! idle-runners (set-remove (ref idle-runners) runner))
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(log "TM assigns task ~a to runner ~a" task-id runner)
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;; TODO - since we're both adding and removing from this set I'm not sure TRs
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;; need to be making assertions about their idleness
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(on stop (set! idle-runners (set-add (ref idle-runners) runner)))
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(assert (task-assignment runner job-id (task task-id desc)))
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(on (asserted (task-state runner job-id task-id (bind st TaskStateDesc)))
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(match st
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[ACCEPTED #f]
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[RUNNING #f]
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[OVERLOAD/ts
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(set! status OVERLOAD/ts)]
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[(finished discard)
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(set! status st)]))))))))
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;; ---------------------------------------------------------------------------------------------------
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;; JobManager
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;; Task -> Bool
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;; Test if the task is ready to run
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(define (task-ready? [t : PendingTask] -> (Maybe ConcreteTask))
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(match t
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[(task (bind tid TaskID) (map-work (bind s String)))
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;; having to re-produce this is directly bc of no occurrence typing
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(some (task tid (map-work s)))]
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[(task (bind tid TaskID) (reduce-work (right (bind v1 TaskResult))
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(right (bind v2 TaskResult))))
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(some (task tid (reduce-work v1 v2)))]
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[discard
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none]))
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;; Task Id Any -> Task
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;; If the given task is waiting for this data, replace the waiting ID with the data
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(define (task+data [t : PendingTask]
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[id : TaskID]
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[data : TaskResult]
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-> PendingTask)
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(match t
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[(task (bind tid TaskID)
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(reduce-work (left id) (bind r (Either TaskID TaskResult))))
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(task tid (reduce-work (right data) r))]
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[(task (bind tid TaskID)
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(reduce-work (bind l (Either TaskID TaskResult)) (left id)))
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(task tid (reduce-work l (right data)))]
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[discard t]))
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(require/typed "flink-support.rkt"
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[split-at/lenient- : (∀ (X) (→fn (List X) Int (List (List X))))])
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(define (∀ (X) (split-at/lenient [xs : (List X)]
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[n : Int]
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-> (Tuple (List X) (List X))))
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(define l (split-at/lenient- xs n))
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(tuple (first l) (second l)))
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(define (partition-ready-tasks [tasks : (List PendingTask)]
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-> (Tuple (List PendingTask)
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(List ConcreteTask)))
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(define part (inst partition/either PendingTask PendingTask ConcreteTask))
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(part tasks
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(lambda ([t : PendingTask])
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(match (task-ready? t)
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[(some (bind ct ConcreteTask))
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(right ct)]
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[none
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(left t)]))))
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(define (spawn-job-manager)
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(spawn τc
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(start-facet jm
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(assert (job-manager-alive))
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(log "Job Manager Up")
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;; keep track of task managers, how many slots they say are open, and how many tasks we have assigned.
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(define/query-hash task-managers (task-manager (bind id ID) (bind slots Int)) id slots
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#;#:on-add #;(log "JM learns that ~a has ~v slots" id slots))
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;; (Hashof TaskManagerID Nat)
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;; to better understand the supply of slots for each task manager, keep track of the number
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;; of requested tasks that we have yet to hear back about
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(field [requests-in-flight (Hash ID Int) (hash)])
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(define (slots-available)
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(for/sum ([(id v) (ref task-managers)])
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(max 0 (- v (hash-ref/failure (ref requests-in-flight) id 0)))))
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;; ID -> Void
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;; mark that we have requested the given task manager to perform a task
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(define (take-slot! [id : ID])
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(log "JM assigns a task to ~a" id)
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(set! requests-in-flight (hash-update/failure (ref requests-in-flight) id add1 0)))
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;; ID -> Void
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;; mark that we have heard back from the given manager about a requested task
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(define (received-answer! [id : ID])
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(set! requests-in-flight (hash-update (ref requests-in-flight) id sub1)))
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(during (job (bind job-id ID) (bind tasks (List PendingTask)))
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(log "JM receives job ~a" job-id)
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(define-tuple (not-ready ready) (partition-ready-tasks tasks))
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(field [ready-tasks (List ConcreteTask) ready]
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[waiting-tasks (List PendingTask) not-ready]
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[tasks-in-progress Int 0])
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(begin/dataflow
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(define slots (slots-available))
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(define-tuple (ts readys)
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(split-at/lenient (ref ready-tasks) slots))
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(for ([t ts])
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#f
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#;(perform-task t push-results))
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(unless (empty? ts)
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;; the empty? check may be necessary to avoid a dataflow loop
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(set! ready-tasks readys)))
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;; Task -> Void
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(define (add-ready-task! [t : ConcreteTask])
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;; TODO - use functional-queue.rkt from ../../
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(match-define (task (bind tid TaskID) discard) t)
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(log "JM marks task ~a as ready" tid)
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(set! ready-tasks (cons t (ref ready-tasks))))
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;; ID Data -> Void
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;; Update any dependent tasks with the results of the given task, moving
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;; them to the ready queue when possible
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(define (push-results [task-id : TaskID]
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[data : TaskResult])
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(cond
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[(and (zero? (ref tasks-in-progress))
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(empty? (ref ready-tasks))
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(empty? (ref waiting-tasks)))
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(log "JM finished with job ~a" job-id)
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(start-facet done (assert (job-finished job-id data)))]
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[else
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;; TODO - in MapReduce, there should be either 1 waiting task, or 0, meaning the job is done.
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(define still-waiting
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(for/fold ([ts : (List PendingTask) (list)])
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([t (ref waiting-tasks)])
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(define t+ (task+data t task-id data))
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(match (task-ready? t+)
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[(some (bind ready ConcreteTask))
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(add-ready-task! ready)
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ts]
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[discard
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(cons t+ ts)])))
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(set! waiting-tasks still-waiting)]))
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;; Task (ID TaskResult -> Void) -> Void
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;; Requires (task-ready? t)
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(define (perform-task [t : ConcreteTask]
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[k : (→fn TaskID TaskResult (Tuple))]
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-> ★/t)
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(start-facet perform
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(on start (set! tasks-in-progress (add1 (ref tasks-in-progress))))
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(on stop (set! tasks-in-progress (sub1 (ref tasks-in-progress))))
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(match-define (task (bind this-id TaskID) (bind desc ConcreteWork)) t)
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(log "JM begins on task ~a" this-id)
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(define (select-a-task-manager)
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(start-facet this-facet
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(begin/dataflow
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(define mngr?
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(for/first ([(id slots) (ref task-managers)]
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#:when (positive? (- slots (hash-ref/failure (ref requests-in-flight) id 0))))
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id))
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(match mngr?
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[(some (bind mngr ID))
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(take-slot! mngr)
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(stop this-facet
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#;(assign-task mngr))]
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[none
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#f])
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#f)))
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;; ID -> ...
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(define (assign-task [mngr : ID])
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(start-facet this-facet
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(on (retracted (task-manager mngr discard))
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;; our task manager has crashed
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(stop this-facet (select-a-task-manager)))
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(on start
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;; N.B. when this line was here, and not after `(when mngr ...)` above,
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;; things didn't work. I think that due to script scheduling, all ready
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;; tasks were being assigned to the manager
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#;(take-slot! mngr)
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(start-facet take-slot
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(stop-when (asserted (task-state mngr job-id this-id discard))
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(received-answer! mngr)))
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#;(task-assigner t job-id mngr
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(lambda ()
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;; need to find a new task manager
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;; don't think we need a release-slot! here, because if we've heard back from a task manager,
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;; they should have told us a different slot count since we tried to give them work
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(log "JM overloaded manager ~a with task ~a" mngr this-id)
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(stop-facet this-facet (select-a-task-manager)))
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(lambda (results)
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(log "JM receives the results of task ~a" this-id)
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(stop-facet perform (k this-id results)))))))
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(on start (select-a-task-manager))))
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#f))))
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