utxoset: Fix parallel script checking to use only as many threads as CPUs

src/blockdata/utxoset.rs

@@ -18,8 +18,10 @@
 //! index of UTXOs.
 //!
 
+use std::cmp;
 use std::collections::HashMap;
 use std::mem;
+use std::os::num_cpus;
 use std::sync::Future;
 
 use blockdata::transaction::{Transaction, TxOut};
@@ -207,11 +209,17 @@ impl UtxoSet {
       let mut future_vec = Vec::with_capacity(block.txdata.len() - 1);
       // skip the genesis since we don't validate this script. (TODO this might
       // be a consensus bug since we don't even check that the opcodes make sense.)
-      for tx in block.txdata.iter().skip(1) {
+      let n_threads = cmp::min(block.txdata.len() - 1, num_cpus());
+      for j in range(0, n_threads) {
+        let n_elems = block.txdata.len() - 1;
+        let start = 1 + j * n_elems / n_threads;
+        let end = cmp::min(n_elems, 1 + (j + 1) * n_elems / n_threads);
+
         let s = self as *mut _ as *const UtxoSet;
-        let tx = tx as *const _;
+        let txes = &block.txdata as *const _;
         future_vec.push(Future::spawn(proc() {
-          let tx = unsafe {&*tx};
+          let txes = unsafe {&*txes};
+          for tx in txes.slice(start, end).iter() {
             for (n, input) in tx.input.iter().enumerate() {
               let txo = unsafe { (*s).get_utxo(input.prev_hash, input.prev_index) };
               match txo {
@@ -241,6 +249,7 @@ impl UtxoSet {
                 None => { return false; }
               }
             }
+          }
           true
         }));
       }