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110 lines
2.8 KiB
Go
110 lines
2.8 KiB
Go
package batch
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import (
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"sync"
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"time"
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"github.com/lightningnetwork/lnd/kvdb"
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)
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// TimeScheduler is a batching engine that executes requests within a fixed
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// horizon. When the first request is received, a TimeScheduler waits a
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// configurable duration for other concurrent requests to join the batch. Once
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// this time has elapsed, the batch is closed and executed. Subsequent requests
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// are then added to a new batch which undergoes the same process.
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type TimeScheduler struct {
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db kvdb.Backend
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locker sync.Locker
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duration time.Duration
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mu sync.Mutex
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b *batch
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}
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// NewTimeScheduler initializes a new TimeScheduler with a fixed duration at
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// which to schedule batches. If the operation needs to modify a higher-level
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// cache, the cache's lock should be provided to so that external consistency
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// can be maintained, as successful db operations will cause a request's
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// OnCommit method to be executed while holding this lock.
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func NewTimeScheduler(db kvdb.Backend, locker sync.Locker,
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duration time.Duration) *TimeScheduler {
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return &TimeScheduler{
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db: db,
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locker: locker,
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duration: duration,
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}
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}
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// Execute schedules the provided request for batch execution along with other
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// concurrent requests. The request will be executed within a fixed horizon,
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// parameterizeed by the duration of the scheduler. The error from the
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// underlying operation is returned to the caller.
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//
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// NOTE: Part of the Scheduler interface.
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func (s *TimeScheduler) Execute(r *Request) error {
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req := request{
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Request: r,
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errChan: make(chan error, 1),
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}
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// Add the request to the current batch. If the batch has been cleared
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// or no batch exists, create a new one.
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s.mu.Lock()
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if s.b == nil {
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s.b = &batch{
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db: s.db,
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clear: s.clear,
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locker: s.locker,
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}
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time.AfterFunc(s.duration, s.b.trigger)
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}
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s.b.reqs = append(s.b.reqs, &req)
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// If this is a non-lazy request, we'll execute the batch immediately.
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if !r.lazy {
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go s.b.trigger()
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}
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s.mu.Unlock()
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// Wait for the batch to process the request. If the batch didn't
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// ask us to execute the request individually, simply return the error.
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err := <-req.errChan
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if err != errSolo {
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return err
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}
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// Obtain exclusive access to the cache if this scheduler needs to
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// modify the cache in OnCommit.
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if s.locker != nil {
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s.locker.Lock()
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defer s.locker.Unlock()
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}
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// Otherwise, run the request on its own.
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commitErr := kvdb.Update(s.db, req.Update, func() {
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if req.Reset != nil {
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req.Reset()
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}
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})
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// Finally, return the commit error directly or execute the OnCommit
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// closure with the commit error if present.
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if req.OnCommit != nil {
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return req.OnCommit(commitErr)
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}
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return commitErr
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}
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// clear resets the scheduler's batch to nil so that no more requests can be
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// added.
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func (s *TimeScheduler) clear(b *batch) {
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s.mu.Lock()
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if s.b == b {
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s.b = nil
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}
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s.mu.Unlock()
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}
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