Add support for getpriority and setpriority to the SysResource portability header

Summary: It's not a perfect mapping, but it's good enough.

Reviewed By: yfeldblum

Differential Revision: D9569405

fbshipit-source-id: 7559fb94f8a57717b5a594be0c05a99ac88c6c6e

folly/portability/SysResource.cpp

@@ -16,6 +16,8 @@
 
 #include <folly/portability/SysResource.h>
 
+#include <errno.h>
+
 #ifdef _WIN32
 #include <folly/portability/Windows.h>
 
@@ -41,5 +43,64 @@ int setrlimit(int /* type */, rlimit* /* src */) {
   // We couldn't set the stack size at runtime even if we wanted to.
   return 0;
 }
+
+int getpriority(int which, int who) {
+  if (which != PRIO_PROCESS || who != 0) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  auto ret = GetPriorityClass(GetCurrentProcess());
+  switch (ret) {
+    case 0:
+      errno = EACCES;
+      return -1;
+    case IDLE_PRIORITY_CLASS:
+      return 39;
+    case BELOW_NORMAL_PRIORITY_CLASS:
+      return 30;
+    case NORMAL_PRIORITY_CLASS:
+      return 20;
+    case ABOVE_NORMAL_PRIORITY_CLASS:
+      return 10;
+    case HIGH_PRIORITY_CLASS:
+      return 0;
+    case REALTIME_PRIORITY_CLASS:
+      // I'd return -1 if it weren't an error :(
+      // Realtime priority processes can't be set
+      // through these APIs because it's a terrible idea.
+      return 0;
+    default:
+      errno = EINVAL;
+      return -1;
+  }
+}
+
+int setpriority(int which, int who, int value) {
+  if (which != PRIO_PROCESS || who != 0) {
+    errno = EINVAL;
+    return -1;
+  }
+
+  auto newClass = [value] {
+    if (value >= 39) {
+      return IDLE_PRIORITY_CLASS;
+    } else if (value >= 30) {
+      return BELOW_NORMAL_PRIORITY_CLASS;
+    } else if (value >= 20) {
+      return NORMAL_PRIORITY_CLASS;
+    } else if (value >= 10) {
+      return ABOVE_NORMAL_PRIORITY_CLASS;
+    } else {
+      return HIGH_PRIORITY_CLASS;
+    }
+  }();
+
+  if (!SetPriorityClass(GetCurrentProcess(), newClass)) {
+    errno = EACCES;
+    return -1;
+  }
+  return 0;
+}
 }
 #endif

folly/portability/SysResource.h

@@ -23,6 +23,8 @@
 
 #include <folly/portability/SysTime.h>
 
+#define PRIO_PROCESS 1
+
 #define RLIMIT_CORE 0
 #define RLIMIT_NOFILE 0
 #define RLIMIT_DATA 0
@@ -62,5 +64,8 @@ extern "C" {
 int getrlimit(int type, rlimit* dst);
 int getrusage(int who, rusage* usage);
 int setrlimit(int type, rlimit* src);
+
+int getpriority(int which, int who);
+int setpriority(int which, int who, int value);
 }
 #endif