Add thread_priority::highest, comments.

include/bitcoin/network/async/thread.hpp

@@ -28,6 +28,7 @@ namespace network {
 
 enum class thread_priority
 {
+    highest,
     high,
     normal,
     low,

src/async/thread.cpp

@@ -22,18 +22,24 @@
 
 #ifdef HAVE_MSC
     #include <windows.h>
+    // #define THREAD_PRIORITY_IDLE            -15
+    // #define THREAD_PRIORITY_LOWEST          -2
+    // #define THREAD_PRIORITY_BELOW_NORMAL    -1
+    // #define THREAD_PRIORITY_NORMAL           0
+    // #define THREAD_PRIORITY_ABOVE_NORMAL     1
+    // #define THREAD_PRIORITY_HIGHEST          2
+    // #define THREAD_PRIORITY_TIME_CRITICAL    15
+    // #define THREAD_PRIORITY_ERROR_RETURN    (MAXLONG)
 #else
     #include <unistd.h>
     #include <pthread.h>
     #include <sys/resource.h>
     #include <sys/types.h>
-    #ifndef PRIO_MAX
-        #define PRIO_MAX 20
-    #endif
-    #define THREAD_PRIORITY_ABOVE_NORMAL (-2)
-    #define THREAD_PRIORITY_NORMAL 0
-    #define THREAD_PRIORITY_BELOW_NORMAL 2
-    #define THREAD_PRIORITY_LOWEST PRIO_MAX
+    #define THREAD_PRIORITY_HIGHEST             -20
+    #define THREAD_PRIORITY_ABOVE_NORMAL        -2
+    #define THREAD_PRIORITY_NORMAL               0
+    #define THREAD_PRIORITY_BELOW_NORMAL         2
+    #define THREAD_PRIORITY_LOWEST               20
 #endif
 
 namespace libbitcoin {
@@ -50,22 +56,36 @@ static int get_priority(thread_priority priority) NOEXCEPT
             return THREAD_PRIORITY_BELOW_NORMAL;
         case thread_priority::high:
             return THREAD_PRIORITY_ABOVE_NORMAL;
+        case thread_priority::highest:
+            return THREAD_PRIORITY_HIGHEST;
         default:
         case thread_priority::normal:
             return THREAD_PRIORITY_NORMAL;
     }
 }
 
-// Set the thread priority (or process if thread priority is not available).
+// Set the thread priority.
+// TODO: handle error conditions.
+// TODO: handle potential lack of PRIO_THREAD
+// TODO: use proper non-win32 priority levels.
+// TODO: Linux: pthread_setschedprio()
+// TOOD: macOS: somethign else.
 void set_priority(thread_priority priority) NOEXCEPT
 {
     const auto prioritization = get_priority(priority);
 
 #if defined(HAVE_MSC)
+    // learn.microsoft.com/en-us/windows/win32/api/processthreadsapi/
+    // nf-processthreadsapi-getthreadpriority
     SetThreadPriority(GetCurrentThread(), prioritization);
+
 #elif defined(PRIO_THREAD)
+    // lore.kernel.org/lkml/1220278355.3866.21.camel@localhost.localdomain/
     setpriority(PRIO_THREAD, pthread_self(), prioritization);
+
 #else
+    // BUGBUG: This will set all threads in the process.
+    // man7.org/linux/man-pages/man3/pthread_self.3.html
     setpriority(PRIO_PROCESS, getpid(), prioritization);
 #endif
 }

test/async/thread.cpp

@@ -65,6 +65,8 @@ BOOST_AUTO_TEST_CASE(thread__set_thread_priorites__all__set_as_expected)
     // Save so we can restore at the end of this test case.
     const int save = get_thread_priority_test();
 
+    set_priority(thread_priority::highest);
+    BOOST_REQUIRE_EQUAL(THREAD_PRIORITY_HIGHEST, get_thread_priority_test());
     set_priority(thread_priority::high);
     BOOST_REQUIRE_EQUAL(THREAD_PRIORITY_ABOVE_NORMAL, get_thread_priority_test());
     set_priority(thread_priority::normal);
@@ -87,6 +89,7 @@ BOOST_AUTO_TEST_CASE(thread__set_thread_priorites__all__set_as_expected)
     const int save = get_thread_priority_test();
 
     // Haven't had any luck matching the set and get priority calls as in win.
+    BOOST_REQUIRE_NO_THROW(set_priority(thread_priority::highest));
     BOOST_REQUIRE_NO_THROW(set_priority(thread_priority::high));
     BOOST_REQUIRE_NO_THROW(set_priority(thread_priority::normal));
     BOOST_REQUIRE_NO_THROW(set_priority(thread_priority::low));