refactor: Move ScheduleBatchPriority to its own file

With the previous move of AlertNotify out of the validation file, and
thus out of the kernel library, ScheduleBatchPriority is the last
remaining function used by the kernel library from util/system. Move it
to its own file, such that util/system can be moved out of the util
library in the following few commits.

Moving util/system out of the kernel library removes further networking
as well as shell related code from it.

Author: TheCharlatan

src/Makefile.am

@@ -280,6 +280,7 @@ BITCOIN_CORE_H = \
   txrequest.h \
   undo.h \
   util/asmap.h \
+  util/batchpriority.h \
   util/bip32.h \
   util/bitdeque.h \
   util/bytevectorhash.h \
@@ -711,6 +712,7 @@ libbitcoin_util_a_SOURCES = \
   support/cleanse.cpp \
   sync.cpp \
   util/asmap.cpp \
+  util/batchpriority.cpp \
   util/bip32.cpp \
   util/bytevectorhash.cpp \
   util/chaintype.cpp \
@@ -963,6 +965,7 @@ libbitcoinkernel_la_SOURCES = \
   txdb.cpp \
   txmempool.cpp \
   uint256.cpp \
+  util/batchpriority.cpp \
   util/chaintype.cpp \
   util/check.cpp \
   util/exception.cpp \
@@ -978,7 +981,6 @@ libbitcoinkernel_la_SOURCES = \
   util/string.cpp \
   util/syscall_sandbox.cpp \
   util/syserror.cpp \
-  util/system.cpp \
   util/thread.cpp \
   util/threadnames.cpp \
   util/time.cpp \

src/node/blockstorage.cpp

@@ -17,6 +17,7 @@
 #include <signet.h>
 #include <streams.h>
 #include <undo.h>
+#include <util/batchpriority.h>
 #include <util/fs.h>
 #include <util/syscall_sandbox.h>
 #include <util/system.h>

src/util/batchpriority.cpp

@@ -0,0 +1,26 @@
+// Copyright (c) 2023 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <logging.h>
+#include <util/syserror.h>
+
+#if (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
+#include <pthread.h>
+#include <pthread_np.h>
+#endif
+
+#ifndef WIN32
+#include <sched.h>
+#endif
+
+void ScheduleBatchPriority()
+{
+#ifdef SCHED_BATCH
+    const static sched_param param{};
+    const int rc = pthread_setschedparam(pthread_self(), SCHED_BATCH, &param);
+    if (rc != 0) {
+        LogPrintf("Failed to pthread_setschedparam: %s\n", SysErrorString(rc));
+    }
+#endif
+}

src/util/batchpriority.h

@@ -0,0 +1,15 @@
+// Copyright (c) 2023 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_BATCHPRIORITY_H
+#define BITCOIN_UTIL_BATCHPRIORITY_H
+
+/**
+ * On platforms that support it, tell the kernel the calling thread is
+ * CPU-intensive and non-interactive. See SCHED_BATCH in sched(7) for details.
+ *
+ */
+void ScheduleBatchPriority();
+
+#endif // BITCOIN_UTIL_BATCHPRIORITY_H

src/util/system.cpp

@@ -7,16 +7,9 @@
 
 #include <logging.h>
 #include <util/string.h>
-#include <util/syserror.h>
 #include <util/time.h>
 
-#if (defined(__FreeBSD__) || defined(__OpenBSD__) || defined(__DragonFly__))
-#include <pthread.h>
-#include <pthread_np.h>
-#endif
-
 #ifndef WIN32
-#include <sched.h>
 #include <sys/stat.h>
 #else
 #include <codecvt>
@@ -112,14 +105,3 @@ int64_t GetStartupTime()
 {
     return nStartupTime;
 }
-
-void ScheduleBatchPriority()
-{
-#ifdef SCHED_BATCH
-    const static sched_param param{};
-    const int rc = pthread_setschedparam(pthread_self(), SCHED_BATCH, &param);
-    if (rc != 0) {
-        LogPrintf("Failed to pthread_setschedparam: %s\n", SysErrorString(rc));
-    }
-#endif
-}

src/util/system.h

@@ -36,13 +36,6 @@ void runCommand(const std::string& strCommand);
  */
 int GetNumCores();
 
-/**
- * On platforms that support it, tell the kernel the calling thread is
- * CPU-intensive and non-interactive. See SCHED_BATCH in sched(7) for details.
- *
- */
-void ScheduleBatchPriority();
-
 namespace util {
 
 //! Simplification of std insertion