Parallelize script verification

* During block verification (when parallelism is requested), script
  check actions are stored instead of being executed immediately.
* After every processed transactions, its signature actions are
  pushed to a CScriptCheckQueue, which maintains a queue and some
  synchronization mechanism.
* Two or more threads (if enabled) start processing elements from
  this queue,
* When the block connection code is finished processing transactions,
  it joins the worker pool until the queue is empty.

As cs_main is held the entire time, and all verification must be
finished before the block continues processing, this does not reach
the best possible performance. It is a less drastic change than
some more advanced mechanisms (like doing verification out-of-band
entirely, and rolling back blocks when a failure is detected).

The -par=N flag controls the number of threads (1-16). 0 means auto,
and is the default.

1 files changed, 20 insertions, 0 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 557c23fc92..087750cf90 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -84,6 +84,10 @@ void Shutdown(void* parg)
         fShutdown = true;
         nTransactionsUpdated++;
         bitdb.Flush(false);
+        {
+            LOCK(cs_main);
+            ThreadScriptCheckQuit();
+        }
         StopNode();
         {
             LOCK(cs_main);
@@ -303,6 +307,7 @@ std::string HelpMessage()
         "  -checklevel=<n>        " + _("How thorough the block verification is (0-6, default: 1)") + "\n" +
         "  -loadblock=<file>      " + _("Imports blocks from external blk000??.dat file") + "\n" +
         "  -reindex               " + _("Rebuild blockchain index from current blk000??.dat files") + "\n" +
+        "  -par=N                 " + _("Set the number of script verification threads (1-16, 0=auto, default: 0)") + "\n" +
 
         "\n" + _("Block creation options:") + "\n" +
         "  -blockminsize=<n>      "   + _("Set minimum block size in bytes (default: 0)") + "\n" +
@@ -484,6 +489,15 @@ bool AppInit2()
     fDebug = GetBoolArg("-debug");
     fBenchmark = GetBoolArg("-benchmark");
 
+    // -par=0 means autodetect, but nScriptCheckThreads==0 means no concurrency
+    nScriptCheckThreads = GetArg("-par", 0);
+    if (nScriptCheckThreads == 0)
+        nScriptCheckThreads = boost::thread::hardware_concurrency();
+    if (nScriptCheckThreads <= 1) 
+        nScriptCheckThreads = 0;
+    else if (nScriptCheckThreads > MAX_SCRIPTCHECK_THREADS)
+        nScriptCheckThreads = MAX_SCRIPTCHECK_THREADS;
+
     // -debug implies fDebug*
     if (fDebug)
         fDebugNet = true;
@@ -579,6 +593,12 @@ bool AppInit2()
     if (fDaemon)
         fprintf(stdout, "Bitcoin server starting\n");
 
+    if (nScriptCheckThreads) {
+        printf("Using %u threads for script verification\n", nScriptCheckThreads);
+        for (int i=0; i<nScriptCheckThreads-1; i++)
+            NewThread(ThreadScriptCheck, NULL);
+    }
+
     int64 nStart;
 
     // ********************************************************* Step 5: verify database integrity