path: root/core/nonblocking.go

// Copyright 2018 The dexon-consensus Authors
// This file is part of the dexon-consensus library.
//
// The dexon-consensus 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 dexon-consensus 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 dexon-consensus library. If not, see
// <http://www.gnu.org/licenses/>.

package core

import (
    "fmt"
    "sync"

    "github.com/dexon-foundation/dexon-consensus/common"
    "github.com/dexon-foundation/dexon-consensus/core/types"
)

type blockConfirmedEvent struct {
    block *types.Block
}

type blockDeliveredEvent struct {
    blockHash     common.Hash
    blockPosition types.Position
    rand          []byte
}

// nonBlocking implements these interfaces and is a decorator for
// them that makes the methods to be non-blocking.
//  - Application
//  - Debug
//  - It also provides nonblockig for db update.
type nonBlocking struct {
    app          Application
    debug        Debug
    eventChan    chan interface{}
    events       []interface{}
    eventsChange *sync.Cond
    running      sync.WaitGroup
}

func newNonBlocking(app Application, debug Debug) *nonBlocking {
    nonBlockingModule := &nonBlocking{
        app:          app,
        debug:        debug,
        eventChan:    make(chan interface{}, 6),
        events:       make([]interface{}, 0, 100),
        eventsChange: sync.NewCond(&sync.Mutex{}),
    }
    go nonBlockingModule.run()
    return nonBlockingModule
}

func (nb *nonBlocking) addEvent(event interface{}) {
    nb.eventsChange.L.Lock()
    defer nb.eventsChange.L.Unlock()
    nb.events = append(nb.events, event)
    nb.eventsChange.Broadcast()
}

func (nb *nonBlocking) run() {
    // This go routine consume the first event from events and call the
    // corresponding methods of Application/Debug/db.
    for {
        var event interface{}
        func() {
            nb.eventsChange.L.Lock()
            defer nb.eventsChange.L.Unlock()
            for len(nb.events) == 0 {
                nb.eventsChange.Wait()
            }
            event = nb.events[0]
            nb.events = nb.events[1:]
            nb.running.Add(1)
        }()
        switch e := event.(type) {
        case blockConfirmedEvent:
            nb.app.BlockConfirmed(*e.block)
        case blockDeliveredEvent:
            nb.app.BlockDelivered(e.blockHash, e.blockPosition, e.rand)
        default:
            fmt.Printf("Unknown event %v.", e)
        }
        nb.running.Done()
        nb.eventsChange.Broadcast()
    }
}

// wait will wait for all event in events finishes.
func (nb *nonBlocking) wait() {
    nb.eventsChange.L.Lock()
    defer nb.eventsChange.L.Unlock()
    for len(nb.events) > 0 {
        nb.eventsChange.Wait()
    }
    nb.running.Wait()
}

// PreparePayload cannot be non-blocking.
func (nb *nonBlocking) PreparePayload(position types.Position) ([]byte, error) {
    return nb.app.PreparePayload(position)
}

// PrepareWitness cannot be non-blocking.
func (nb *nonBlocking) PrepareWitness(height uint64) (types.Witness, error) {
    return nb.app.PrepareWitness(height)
}

// VerifyBlock cannot be non-blocking.
func (nb *nonBlocking) VerifyBlock(block *types.Block) types.BlockVerifyStatus {
    return nb.app.VerifyBlock(block)
}

// BlockConfirmed is called when a block is confirmed and added to lattice.
func (nb *nonBlocking) BlockConfirmed(block types.Block) {
    nb.addEvent(blockConfirmedEvent{&block})
}

// BlockDelivered is called when a block is add to the compaction chain.
func (nb *nonBlocking) BlockDelivered(blockHash common.Hash,
    blockPosition types.Position, rand []byte) {
    nb.addEvent(blockDeliveredEvent{
        blockHash:     blockHash,
        blockPosition: blockPosition,
        rand:          rand,
    })
}