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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 ethash
import (
crand "crypto/rand"
"math"
"math/big"
"math/rand"
"runtime"
"sync"
"github.com/ethereum/go-ethereum/common"
"github.com/ethereum/go-ethereum/consensus"
"github.com/ethereum/go-ethereum/core/types"
"github.com/ethereum/go-ethereum/log"
)
// Seal implements consensus.Engine, attempting to find a nonce that satisfies
// the block's difficulty requirements.
func (ethash *Ethash) Seal(chain consensus.ChainReader, block *types.Block, stop <-chan struct{}) (*types.Block, error) {
// If we're running a fake PoW, simply return a 0 nonce immediately
if ethash.fakeMode {
header := block.Header()
header.Nonce, header.MixDigest = types.BlockNonce{}, common.Hash{}
return block.WithSeal(header), nil
}
// If we're running a shared PoW, delegate sealing to it
if ethash.shared != nil {
return ethash.shared.Seal(chain, block, stop)
}
// Create a runner and the multiple search threads it directs
abort := make(chan struct{})
found := make(chan *types.Block)
ethash.lock.Lock()
threads := ethash.threads
if ethash.rand == nil {
seed, err := crand.Int(crand.Reader, big.NewInt(math.MaxInt64))
if err != nil {
ethash.lock.Unlock()
return nil, err
}
ethash.rand = rand.New(rand.NewSource(seed.Int64()))
}
ethash.lock.Unlock()
if threads == 0 {
threads = runtime.NumCPU()
}
if threads < 0 {
threads = 0 // Allows disabling local mining without extra logic around local/remote
}
var pend sync.WaitGroup
for i := 0; i < threads; i++ {
pend.Add(1)
go func(id int, nonce uint64) {
defer pend.Done()
ethash.mine(block, id, nonce, abort, found)
}(i, uint64(ethash.rand.Int63()))
}
// Wait until sealing is terminated or a nonce is found
var result *types.Block
select {
case <-stop:
// Outside abort, stop all miner threads
close(abort)
case result = <-found:
// One of the threads found a block, abort all others
close(abort)
case <-ethash.update:
// Thread count was changed on user request, restart
close(abort)
pend.Wait()
return ethash.Seal(chain, block, stop)
}
// Wait for all miners to terminate and return the block
pend.Wait()
return result, nil
}
// mine is the actual proof-of-work miner that searches for a nonce starting from
// seed that results in correct final block difficulty.
func (ethash *Ethash) mine(block *types.Block, id int, seed uint64, abort chan struct{}, found chan *types.Block) {
// Extract some data from the header
var (
header = block.Header()
hash = header.HashNoNonce().Bytes()
target = new(big.Int).Div(maxUint256, header.Difficulty)
number = header.Number.Uint64()
dataset = ethash.dataset(number)
)
// Start generating random nonces until we abort or find a good one
var (
attempts = int64(0)
nonce = seed
)
logger := log.New("miner", id)
logger.Trace("Started ethash search for new nonces", "seed", seed)
for {
select {
case <-abort:
// Mining terminated, update stats and abort
logger.Trace("Ethash nonce search aborted", "attempts", nonce-seed)
ethash.hashrate.Mark(attempts)
return
default:
// We don't have to update hash rate on every nonce, so update after after 2^X nonces
attempts++
if (attempts % (1 << 15)) == 0 {
ethash.hashrate.Mark(attempts)
attempts = 0
}
// Compute the PoW value of this nonce
digest, result := hashimotoFull(dataset, hash, nonce)
if new(big.Int).SetBytes(result).Cmp(target) <= 0 {
// Correct nonce found, create a new header with it
header = types.CopyHeader(header)
header.Nonce = types.EncodeNonce(nonce)
header.MixDigest = common.BytesToHash(digest)
// Seal and return a block (if still needed)
select {
case found <- block.WithSeal(header):
logger.Trace("Ethash nonce found and reported", "attempts", nonce-seed, "nonce", nonce)
case <-abort:
logger.Trace("Ethash nonce found but discarded", "attempts", nonce-seed, "nonce", nonce)
}
return
}
nonce++
}
}
}
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