// limitNumOrphans limits the number of orphan transactions by evicting a random
// orphan if adding a new one would cause it to overflow the max allowed.
//
// This function MUST be called with the mempool lock held (for writes).
func (mp *txMemPool) limitNumOrphans() error {
if len(mp.orphans)+1 > maxOrphanTransactions {
// Generate a cryptographically random hash.
randHashBytes := make([]byte, btcwire.HashSize)
_, err := rand.Read(randHashBytes)
if err != nil {
return err
}
randHashNum := new(big.Int).SetBytes(randHashBytes)
// Try to find the first entry that is greater than the random
// hash. Use the first entry (which is already pseudorandom due
// to Go's range statement over maps) as a fallback if none of
// the hashes in the orphan pool are larger than the random
// hash.
var foundHash *btcwire.ShaHash
for txHash := range mp.orphans {
if foundHash == nil {
foundHash = &txHash
}
txHashNum := btcchain.ShaHashToBig(&txHash)
if txHashNum.Cmp(randHashNum) > 0 {
foundHash = &txHash
break
}
}
mp.removeOrphan(foundHash)
}
return nil
}
// solveBlock attempts to find some combination of a nonce, extra nonce, and
// current timestamp which makes the passed block hash to a value less than the
// target difficulty. The timestamp is updated periodically and the passed
// block is modified with all tweaks during this process. This means that
// when the function returns true, the block is ready for submission.
//
// This function will return early with false when conditions that trigger a
// stale block such as a new block showing up or periodically when there are
// new transactions and enough time has elapsed without finding a solution.
func (m *CPUMiner) solveBlock(msgBlock *btcwire.MsgBlock, blockHeight int64,
ticker *time.Ticker, quit chan struct{}) bool {
// Choose a random extra nonce offset for this block template and
// worker.
enOffset, err := btcwire.RandomUint64()
if err != nil {
minrLog.Errorf("Unexpected error while generating random "+
"extra nonce offset: %v", err)
enOffset = 0
}
// Create a couple of convenience variables.
header := &msgBlock.Header
targetDifficulty := btcchain.CompactToBig(header.Bits)
// Initial state.
lastGenerated := time.Now()
lastTxUpdate := m.server.txMemPool.LastUpdated()
hashesCompleted := uint64(0)
// Note that the entire extra nonce range is iterated and the offset is
// added relying on the fact that overflow will wrap around 0 as
// provided by the Go spec.
for extraNonce := uint64(0); extraNonce < maxExtraNonce; extraNonce++ {
// Update the extra nonce in the block template with the
// new value by regenerating the coinbase script and
// setting the merkle root to the new value. The
UpdateExtraNonce(msgBlock, blockHeight, extraNonce+enOffset)
// Search through the entire nonce range for a solution while
// periodically checking for early quit and stale block
// conditions along with updates to the speed monitor.
for i := uint32(0); i <= maxNonce; i++ {
select {
case <-quit:
return false
case <-ticker.C:
m.updateHashes <- hashesCompleted
hashesCompleted = 0
// The current block is stale if the best block
// has changed.
bestHash, _ := m.server.blockManager.chainState.Best()
if !header.PrevBlock.IsEqual(bestHash) {
return false
}
// The current block is stale if the memory pool
// has been updated since the block template was
// generated and it has been at least one
// minute.
if lastTxUpdate != m.server.txMemPool.LastUpdated() &&
time.Now().After(lastGenerated.Add(time.Minute)) {
return false
}
UpdateBlockTime(msgBlock, m.server.blockManager)
default:
// Non-blocking select to fall through
}
// Update the nonce and hash the block header. Each
// hash is actually a double sha256 (two hashes), so
// increment the number of hashes completed for each
// attempt accordingly.
header.Nonce = i
hash, _ := header.BlockSha()
hashesCompleted += 2
// The block is solved when the new block hash is less
// than the target difficulty. Yay!
if btcchain.ShaHashToBig(&hash).Cmp(targetDifficulty) <= 0 {
m.updateHashes <- hashesCompleted
return true
}
}
}
return false
}