miner: provide coinbase when starting the miner

This avoids having to query the coinbase when creating the miner, which
in turn eliminates the dreaded startup error when no accounts are set
up. Later, this will also allow us to simply restart the miner when the
user picks a different coinbase.

This causes a lot of changes in other packages. These are included in
this commit because they're impossible to separate.

miner/miner.go

@@ -17,44 +17,34 @@ type Miner struct {
 	MinAcceptedGasPrice *big.Int
 	Extra               string
 
-	Coinbase []byte
-	mining   bool
-
-	pow pow.PoW
+	mining bool
+	eth    core.Backend
+	pow    pow.PoW
 }
 
-func New(coinbase []byte, eth core.Backend, pow pow.PoW, minerThreads int) *Miner {
-	miner := &Miner{
-		Coinbase: coinbase,
-		worker:   newWorker(coinbase, eth),
-		pow:      pow,
-	}
-
-	minerThreads = 1
-	for i := 0; i < minerThreads; i++ {
-		miner.worker.register(NewCpuMiner(i, miner.pow))
-	}
-
-	return miner
+func New(eth core.Backend, pow pow.PoW, minerThreads int) *Miner {
+	// note: minerThreads is currently ignored because
+	// ethash is not thread safe.
+	return &Miner{eth: eth, pow: pow}
 }
 
 func (self *Miner) Mining() bool {
 	return self.mining
 }
 
-func (self *Miner) Start() {
+func (self *Miner) Start(coinbase []byte) {
 	self.mining = true
+	self.worker = newWorker(coinbase, self.eth)
+	self.worker.register(NewCpuMiner(0, self.pow))
 
 	self.pow.(*ethash.Ethash).UpdateDAG()
 
 	self.worker.start()
-
 	self.worker.commitNewWork()
 }
 
 func (self *Miner) Stop() {
 	self.mining = false
-
 	self.worker.stop()
 
 	//self.pow.(*ethash.Ethash).Stop()