Fix segfaults on exiting std.parallelism

std/parallelism.d

@@ -643,7 +643,6 @@ ReturnType!(F) run(F, Args...)(F fpOrDelegate, ref Args args) {
     return fpOrDelegate(args);
 }
 
-
 /**
 Creates a $(D Task) on the GC heap that calls an alias.  This may be executed
 via $(D Task.executeInNewThread) or by submitting to a
@@ -818,6 +817,38 @@ the operating system.
 */
 immutable uint totalCPUs;
 
+/*
+This class serves two purposes:
+
+1.  It distinguishes std.parallelism threads from other threads so that 
+    the std.parallelism daemon threads can be terminated.
+
+2.  It adds a reference to the pool that the thread is a member of,
+    which is also necessary to allow the daemon threads to be properly
+    terminated.
+*/
+private final class ParallelismThread : Thread {
+    this(void delegate() dg) {
+        super(dg);
+    }
+
+    TaskPool pool;
+}
+
+// Kill daemon threads.
+shared static ~this() {
+    auto allThreads = Thread.getAll();
+
+    foreach(thread; allThreads) {
+        auto pthread = cast(ParallelismThread) thread;
+        if(pthread is null) continue;
+        auto pool = pthread.pool;
+        if(!pool.isDaemon) continue;
+        pool.stop();
+        pthread.join();
+    }
+}    
+
 /**
 This class encapsulates a task queue and a set of worker threads.  Its purpose
 is to efficiently map a large number of $(D Task)s onto a smaller number of
@@ -845,7 +876,7 @@ private:
     // Task.executeInNewThread().
     bool isSingleTask;
 
-    Thread[] pool;
+    ParallelismThread[] pool;
     Thread singleTaskThread;
 
     AbstractTask* head;
@@ -1176,9 +1207,10 @@ public:
         workerCondition = new Condition(queueMutex);
         waiterCondition = new Condition(waiterMutex);
 
-        pool = new Thread[nWorkers];
+        pool = new ParallelismThread[nWorkers];
         foreach(ref poolThread; pool) {
-            poolThread = new Thread(&workLoop);
+            poolThread = new ParallelismThread(&workLoop);
+            poolThread.pool = this;
             poolThread.start();
         }
     }