threads: introduce util/threadnames, refactor thread naming

This work is prerequisite to attaching thread names to log lines and deadlock
debug utilities. This code allows setting of an "internal" threadname per
thread on platforms where thread_local is available.

This commit also moves RenameThread() out of a more general module and adds a
numeric suffix to disambiguate between threads with the same name. It
explicitly names a few main threads using the new util::ThreadRename().

src/init.cpp

@@ -42,6 +42,7 @@
 #include <script/sigcache.h>
 #include <scheduler.h>
 #include <shutdown.h>
+#include <util/threadnames.h>
 #include <timedata.h>
 #include <txdb.h>
 #include <txmempool.h>
@@ -208,7 +209,7 @@ void Shutdown(InitInterfaces& interfaces)
     /// for example if the data directory was found to be locked.
     /// Be sure that anything that writes files or flushes caches only does this if the respective
     /// module was initialized.
-    RenameThread("bitcoin-shutoff");
+    util::ThreadRename("shutoff");
     mempool.AddTransactionsUpdated(1);
 
     StopHTTPRPC();
@@ -669,7 +670,7 @@ static void CleanupBlockRevFiles()
 static void ThreadImport(std::vector<fs::path> vImportFiles)
 {
     const CChainParams& chainparams = Params();
-    RenameThread("bitcoin-loadblk");
+    util::ThreadRename("loadblk");
     ScheduleBatchPriority();
 
     {
@@ -1305,7 +1306,7 @@ bool AppInitMain(InitInterfaces& interfaces)
     LogPrintf("Using %u threads for script verification\n", nScriptCheckThreads);
     if (nScriptCheckThreads) {
         for (int i=0; i<nScriptCheckThreads-1; i++)
-            threadGroup.create_thread(&ThreadScriptCheck);
+            threadGroup.create_thread([i]() { return ThreadScriptCheck(i); });
     }
 
     // Start the lightweight task scheduler thread