try to behave better on leorize's laptop (#41)

* try to behave better on leorize's laptop

* bump semaphores version requirement

balls.nimble

@@ -6,6 +6,7 @@ license = "MIT"
 # requires newTreeFrom
 requires "https://github.com/disruptek/grok >= 0.5.0 & < 1.0.0"
 requires "https://github.com/disruptek/ups < 1.0.0"
+requires "https://github.com/disruptek/semaphores >= 0.0.4 & < 1.0.0"
 
 bin = @["balls"]            # build the binary for basic test running
 installExt = @["nim"]       # we need to install balls.nim also

balls/runner.nim

@@ -14,6 +14,7 @@ when not compileOption"threads":
 import std/rlocks
 
 import ups/sanitize
+import semaphores
 
 import balls/spec
 import balls/style
@@ -79,6 +80,12 @@ proc shortPath(fn: string): string =
 proc `$`(p: Profile): string =
   "$#: $# $# $#" % [ short p.fn, $p.cp, $p.gc, $p.opt ]
 
+proc corePhore(): Semaphore =
+  ## produce a semaphore according to the number of available cores
+  result.init 314
+  for core in 1 .. countProcessors():
+    signal result
+
 template cmper(f: untyped) {.dirty.} =
   result = system.cmp(a.`f`, b.`f`)
   if result != 0:
@@ -403,14 +410,22 @@ proc shouldPass(p: Profile): bool =
             if p.gc <= arc:
               result = true
 
+var cores = corePhore()
+
 proc performThreaded(p: Payload) {.thread.} =
+  ## run perform, but do it in a thread with a lock on the compilation cache
   var ran: string
   {.gcsafe.}:
     ran = p.profile.run
     p.status[] = Wait
     withRLock p.cache[]:
-      p.status[] = Runs
-      p.status[] = perform p.profile
+      wait cores
+      try:
+        p.status[] = Runs
+        p.status[] = perform p.profile
+      finally:
+        # indicate that we're done with the core
+        signal cores
 
   # we don't conditionally raise anymore because we don't join threads, so
   # we cannot catch it easily in the parent thread; hence we rely upon the