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// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package bloombits
import (
"sync"
)
// request represents a bloom retrieval task to prioritize and pull from the local
// database or remotely from the network.
type request struct {
section uint64 // Section index to retrieve the a bit-vector from
bit uint // Bit index within the section to retrieve the vector of
}
// response represents the state of a requested bit-vector through a scheduler.
type response struct {
cached []byte // Cached bits to dedup multiple requests
done chan struct{} // Channel to allow waiting for completion
}
// scheduler handles the scheduling of bloom-filter retrieval operations for
// entire section-batches belonging to a single bloom bit. Beside scheduling the
// retrieval operations, this struct also deduplicates the requests and caches
// the results to minimize network/database overhead even in complex filtering
// scenarios.
type scheduler struct {
bit uint // Index of the bit in the bloom filter this scheduler is responsible for
responses map[uint64]*response // Currently pending retrieval requests or already cached responses
lock sync.Mutex // Lock protecting the responses from concurrent access
}
// newScheduler creates a new bloom-filter retrieval scheduler for a specific
// bit index.
func newScheduler(idx uint) *scheduler {
return &scheduler{
bit: idx,
responses: make(map[uint64]*response),
}
}
// run creates a retrieval pipeline, receiving section indexes from sections and
// returning the results in the same order through the done channel. Concurrent
// runs of the same scheduler are allowed, leading to retrieval task deduplication.
func (s *scheduler) run(sections chan uint64, dist chan *request, done chan []byte, quit chan struct{}, wg *sync.WaitGroup) {
// Create a forwarder channel between requests and responses of the same size as
// the distribution channel (since that will block the pipeline anyway).
pend := make(chan uint64, cap(dist))
// Start the pipeline schedulers to forward between user -> distributor -> user
wg.Add(2)
go s.scheduleRequests(sections, dist, pend, quit, wg)
go s.scheduleDeliveries(pend, done, quit, wg)
}
// reset cleans up any leftovers from previous runs. This is required before a
// restart to ensure the no previously requested but never delivered state will
// cause a lockup.
func (s *scheduler) reset() {
s.lock.Lock()
defer s.lock.Unlock()
for section, res := range s.responses {
if res.cached == nil {
delete(s.responses, section)
}
}
}
// scheduleRequests reads section retrieval requests from the input channel,
// deduplicates the stream and pushes unique retrieval tasks into the distribution
// channel for a database or network layer to honour.
func (s *scheduler) scheduleRequests(reqs chan uint64, dist chan *request, pend chan uint64, quit chan struct{}, wg *sync.WaitGroup) {
// Clean up the goroutine and pipeline when done
defer wg.Done()
defer close(pend)
// Keep reading and scheduling section requests
for {
select {
case <-quit:
return
case section, ok := <-reqs:
// New section retrieval requested
if !ok {
return
}
// Deduplicate retrieval requests
unique := false
s.lock.Lock()
if s.responses[section] == nil {
s.responses[section] = &response{
done: make(chan struct{}),
}
unique = true
}
s.lock.Unlock()
// Schedule the section for retrieval and notify the deliverer to expect this section
if unique {
select {
case <-quit:
return
case dist <- &request{bit: s.bit, section: section}:
}
}
select {
case <-quit:
return
case pend <- section:
}
}
}
}
// scheduleDeliveries reads section acceptance notifications and waits for them
// to be delivered, pushing them into the output data buffer.
func (s *scheduler) scheduleDeliveries(pend chan uint64, done chan []byte, quit chan struct{}, wg *sync.WaitGroup) {
// Clean up the goroutine and pipeline when done
defer wg.Done()
defer close(done)
// Keep reading notifications and scheduling deliveries
for {
select {
case <-quit:
return
case idx, ok := <-pend:
// New section retrieval pending
if !ok {
return
}
// Wait until the request is honoured
s.lock.Lock()
res := s.responses[idx]
s.lock.Unlock()
select {
case <-quit:
return
case <-res.done:
}
// Deliver the result
select {
case <-quit:
return
case done <- res.cached:
}
}
}
}
// deliver is called by the request distributor when a reply to a request arrives.
func (s *scheduler) deliver(sections []uint64, data [][]byte) {
s.lock.Lock()
defer s.lock.Unlock()
for i, section := range sections {
if res := s.responses[section]; res != nil && res.cached == nil { // Avoid non-requests and double deliveries
res.cached = data[i]
close(res.done)
}
}
}
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