[llvm][Support] Provide interface to set thread priorities
Summary:
We have a multi-platform thread priority setting function(last piece
landed with D58683), I wanted to make this available to all llvm community,
there seem to be other users of such functionality with portability fixmes:
lib/Support/CrashRecoveryContext.cpp
tools/clang/tools/libclang/CIndex.cpp
Reviewers: gribozavr, ioeric
Subscribers: krytarowski, jfb, kristina, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59130
llvm-svn: 358494
diff --git a/llvm/lib/Support/Unix/Threading.inc b/llvm/lib/Support/Unix/Threading.inc
index 767f626..ed9a965 100644
--- a/llvm/lib/Support/Unix/Threading.inc
+++ b/llvm/lib/Support/Unix/Threading.inc
@@ -217,3 +217,42 @@
#endif
#endif
}
+
+SetThreadPriorityResult llvm::set_thread_priority(ThreadPriority Priority) {
+#if defined(__linux__) && defined(SCHED_IDLE)
+ // Some *really* old glibcs are missing SCHED_IDLE.
+ // http://man7.org/linux/man-pages/man3/pthread_setschedparam.3.html
+ // http://man7.org/linux/man-pages/man2/sched_setscheduler.2.html
+ sched_param priority;
+ // For each of the above policies, param->sched_priority must be 0.
+ priority.sched_priority = 0;
+ // SCHED_IDLE for running very low priority background jobs.
+ // SCHED_OTHER the standard round-robin time-sharing policy;
+ return !pthread_setschedparam(
+ pthread_self(),
+ Priority == ThreadPriority::Background ? SCHED_IDLE : SCHED_OTHER,
+ &priority)
+ ? SetThreadPriorityResult::SUCCESS
+ : SetThreadPriorityResult::FAILURE;
+#elif defined(__APPLE__)
+ // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man2/getpriority.2.html
+ // When setting a thread into background state the scheduling priority is set
+ // to lowest value, disk and network IO are throttled. Network IO will be
+ // throttled for any sockets the thread opens after going into background
+ // state. Any previously opened sockets are not affected.
+
+ // https://developer.apple.com/library/archive/documentation/System/Conceptual/ManPages_iPhoneOS/man3/getiopolicy_np.3.html
+ // I/Os with THROTTLE policy are called THROTTLE I/Os. If a THROTTLE I/O
+ // request occurs within a small time window (usually a fraction of a second)
+ // of another NORMAL I/O request, the thread that issues the THROTTLE I/O is
+ // forced to sleep for a certain interval. This slows down the thread that
+ // issues the THROTTLE I/O so that NORMAL I/Os can utilize most of the disk
+ // I/O bandwidth.
+ return !setpriority(PRIO_DARWIN_THREAD, 0,
+ Priority == ThreadPriority::Background ? PRIO_DARWIN_BG
+ : 0)
+ ? SetThreadPriorityResult::SUCCESS
+ : SetThreadPriorityResult::FAILURE;
+#endif
+ return SetThreadPriorityResult::FAILURE;
+}