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/util/system.cpp

@@ -60,10 +60,6 @@
 #include <shlobj.h>
 #endif
 
-#ifdef HAVE_SYS_PRCTL_H
-#include <sys/prctl.h>
-#endif
-
 #ifdef HAVE_MALLOPT_ARENA_MAX
 #include <malloc.h>
 #endif
@@ -1137,22 +1133,6 @@ void runCommand(const std::string& strCommand)
         LogPrintf("runCommand error: system(%s) returned %d\n", strCommand, nErr);
 }
 
-void RenameThread(const char* name)
-{
-#if defined(PR_SET_NAME)
-    // Only the first 15 characters are used (16 - NUL terminator)
-    ::prctl(PR_SET_NAME, name, 0, 0, 0);
-#elif (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
-    pthread_set_name_np(pthread_self(), name);
-
-#elif defined(MAC_OSX)
-    pthread_setname_np(name);
-#else
-    // Prevent warnings for unused parameters...
-    (void)name;
-#endif
-}
-
 void SetupEnvironment()
 {
 #ifdef HAVE_MALLOPT_ARENA_MAX

src/util/system.h

@@ -20,6 +20,7 @@
 #include <fs.h>
 #include <logging.h>
 #include <sync.h>
+#include <util/threadnames.h>
 #include <tinyformat.h>
 #include <util/memory.h>
 #include <util/time.h>
@@ -325,15 +326,12 @@ std::string HelpMessageOpt(const std::string& option, const std::string& message
  */
 int GetNumCores();
 
-void RenameThread(const char* name);
-
 /**
  * .. and a wrapper that just calls func once
  */
 template <typename Callable> void TraceThread(const char* name,  Callable func)
 {
-    std::string s = strprintf("bitcoin-%s", name);
-    RenameThread(s.c_str());
+    util::ThreadRename(name);
     try
     {
         LogPrintf("%s thread start\n", name);

src/util/threadnames.cpp

@@ -0,0 +1,57 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#if defined(HAVE_CONFIG_H)
+#include <config/bitcoin-config.h>
+#endif
+
+#include <atomic>
+#include <thread>
+
+#include <util/threadnames.h>
+
+#ifdef HAVE_SYS_PRCTL_H
+#include <sys/prctl.h> // For prctl, PR_SET_NAME, PR_GET_NAME
+#endif
+
+//! Set the thread's name at the process level. Does not affect the
+//! internal name.
+static void SetThreadName(const char* name)
+{
+#if defined(PR_SET_NAME)
+    // Only the first 15 characters are used (16 - NUL terminator)
+    ::prctl(PR_SET_NAME, name, 0, 0, 0);
+#elif (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
+    pthread_set_name_np(pthread_self(), name);
+#elif defined(MAC_OSX)
+    pthread_setname_np(name);
+#else
+    // Prevent warnings for unused parameters...
+    (void)name;
+#endif
+}
+
+// If we have thread_local, just keep thread ID and name in a thread_local
+// global.
+#if defined(HAVE_THREAD_LOCAL)
+
+static thread_local std::string g_thread_name;
+const std::string& util::ThreadGetInternalName() { return g_thread_name; }
+//! Set the in-memory internal name for this thread. Does not affect the process
+//! name.
+static void SetInternalName(std::string name) { g_thread_name = std::move(name); }
+
+// Without thread_local available, don't handle internal name at all.
+#else
+
+static const std::string empty_string;
+const std::string& util::ThreadGetInternalName() { return empty_string; }
+static void SetInternalName(std::string name) { }
+#endif
+
+void util::ThreadRename(std::string&& name)
+{
+    SetThreadName(("bitcoin-" + name).c_str());
+    SetInternalName(std::move(name));
+}

src/util/threadnames.h

@@ -0,0 +1,21 @@
+// Copyright (c) 2018 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_UTIL_THREADNAMES_H
+#define BITCOIN_UTIL_THREADNAMES_H
+
+#include <string>
+
+namespace util {
+//! Rename a thread both in terms of an internal (in-memory) name as well
+//! as its system thread name.
+void ThreadRename(std::string&&);
+
+//! Get the thread's internal (in-memory) name; used e.g. for identification in
+//! logging.
+const std::string& ThreadGetInternalName();
+
+} // namespace util
+
+#endif // BITCOIN_UTIL_THREADNAMES_H