Directly return None if tracing is disabled (#8504)

* Directly return None if tracing is disabled

* Address gumbles: release read locks as fast as possible

ethcore/src/client/client.rs

@@ -1868,6 +1868,10 @@ impl BlockChainClient for Client {
 	}
 
 	fn filter_traces(&self, filter: TraceFilter) -> Option<Vec<LocalizedTrace>> {
+		if !self.tracedb.read().tracing_enabled() {
+			return None;
+		}
+
 		let start = self.block_number(filter.range.start)?;
 		let end = self.block_number(filter.range.end)?;
 
@@ -1887,6 +1891,10 @@ impl BlockChainClient for Client {
 	}
 
 	fn trace(&self, trace: TraceId) -> Option<LocalizedTrace> {
+		if !self.tracedb.read().tracing_enabled() {
+			return None;
+		}
+
 		let trace_address = trace.address;
 		self.transaction_address(trace.transaction)
 			.and_then(|tx_address| {
@@ -1896,6 +1904,10 @@ impl BlockChainClient for Client {
 	}
 
 	fn transaction_traces(&self, transaction: TransactionId) -> Option<Vec<LocalizedTrace>> {
+		if !self.tracedb.read().tracing_enabled() {
+			return None;
+		}
+
 		self.transaction_address(transaction)
 			.and_then(|tx_address| {
 				self.block_number(BlockId::Hash(tx_address.block_hash))
@@ -1904,6 +1916,10 @@ impl BlockChainClient for Client {
 	}
 
 	fn block_traces(&self, block: BlockId) -> Option<Vec<LocalizedTrace>> {
+		if !self.tracedb.read().tracing_enabled() {
+			return None;
+		}
+
 		self.block_number(block)
 			.and_then(|number| self.tracedb.read().block_traces(number))
 	}