1 files changed, 96 insertions, 0 deletions
diff --git a/lib/pure/concurrency/cpuload.nim b/lib/pure/concurrency/cpuload.nim
new file mode 100644
index 000000000..3cf6a7392
--- /dev/null
+++ b/lib/pure/concurrency/cpuload.nim
@@ -0,0 +1,96 @@
+#
+#
+#            Nimrod's Runtime Library
+#        (c) Copyright 2014 Andreas Rumpf
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module implements a helper for a thread pool to determine whether
+## creating a thread is a good idea.
+
+when defined(windows):
+  import winlean, os, strutils, math
+
+  proc `-`(a, b: TFILETIME): int64 = a.rdFileTime - b.rdFileTime
+elif defined(linux):
+  from cpuinfo import countProcessors
+
+type
+  ThreadPoolAdvice* = enum
+    doNothing,
+    doCreateThread,  # create additional thread for throughput
+    doShutdownThread # too many threads are busy, shutdown one
+
+  ThreadPoolState* = object
+    when defined(windows):
+      prevSysKernel, prevSysUser, prevProcKernel, prevProcUser: TFILETIME
+    calls*: int
+
+proc advice*(s: var ThreadPoolState): ThreadPoolAdvice =
+  when defined(windows):
+    var
+      sysIdle, sysKernel, sysUser,
+        procCreation, procExit, procKernel, procUser: TFILETIME
+    if getSystemTimes(sysIdle, sysKernel, sysUser) == 0 or
+        getProcessTimes(THandle(-1), procCreation, procExit, 
+                        procKernel, procUser) == 0:
+      return doNothing
+    if s.calls > 0:
+      let
+        sysKernelDiff = sysKernel - s.prevSysKernel
+        sysUserDiff = sysUser - s.prevSysUser
+
+        procKernelDiff = procKernel - s.prevProcKernel
+        procUserDiff = procUser - s.prevProcUser
+
+        sysTotal = int(sysKernelDiff + sysUserDiff)
+        procTotal = int(procKernelDiff + procUserDiff)
+      # total CPU usage < 85% --> create a new worker thread.
+      # Measurements show that 100% and often even 90% is not reached even
+      # if all my cores are busy.
+      if sysTotal == 0 or procTotal / sysTotal < 0.85:
+        result = doCreateThread
+    s.prevSysKernel = sysKernel
+    s.prevSysUser = sysUser
+    s.prevProcKernel = procKernel
+    s.prevProcUser = procUser
+  elif defined(linux):
+    proc fscanf(c: TFile, frmt: cstring) {.varargs, importc, 
+      header: "<stdio.h>".}
+
+    var f = open("/proc/loadavg")
+    var b: float
+    var busy, total: int
+    fscanf(f,"%lf %lf %lf %ld/%ld",
+           addr b, addr b, addr b, addr busy, addr total)
+    f.close()
+    let cpus = countProcessors()
+    if busy-1 < cpus:
+      result = doCreateThread
+    elif busy-1 >= cpus*2:
+      result = doShutdownThread
+    else:
+      result = doNothing
+  else:
+    # XXX implement this for other OSes
+    result = doNothing
+  inc s.calls
+
+when isMainModule:
+  proc busyLoop() =
+    while true:
+      discard random(80)
+      os.sleep(100)
+
+  spawn busyLoop()
+  spawn busyLoop()
+  spawn busyLoop()
+  spawn busyLoop()
+
+  var s: ThreadPoolState
+
+  for i in 1 .. 70:
+    echo advice(s)
+    os.sleep(1000)