libutil: add async io roots to threadpool threads

this needs a new method because overloading rules would make a pair of
methods taking `std::function`s of different argument types ambiguous.
we could've turned enqueue into a template and made `enqueueWithAio` a
private method too, but the necessary template magic is wasted on this

Change-Id: I93ccfde07126c287ad2a4dc5a07caec6a9d83944

lix/libutil/thread-pool.cc

@@ -41,7 +41,7 @@ void ThreadPool::shutdown()
         thr.join();
 }
 
-void ThreadPool::enqueue(const work_t & t)
+void ThreadPool::enqueueWithAio(const work_t & t)
 {
     auto state(state_.lock());
     if (quit)
@@ -95,6 +95,8 @@ void ThreadPool::doWork()
     bool didWork = false;
     std::exception_ptr exc;
 
+    AsyncIoRoot aio;
+
     while (true) {
         work_t w;
         {
@@ -157,7 +159,7 @@ void ThreadPool::doWork()
         }
 
         try {
-            w();
+            w(aio);
         } catch (...) {
             exc = std::current_exception();
         }

lix/libutil/thread-pool.hh

@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "lix/libutil/async.hh"
 #include "lix/libutil/error.hh"
 #include "lix/libutil/sync.hh"
 
@@ -31,12 +32,17 @@ public:
      *
      * \todo use std::packaged_task?
      */
-    typedef std::function<void()> work_t;
+    typedef std::function<void(AsyncIoRoot &)> work_t;
 
     /**
      * Enqueue a function to be executed by the thread pool.
      */
-    void enqueue(const work_t & t);
+    void enqueueWithAio(const work_t & t);
+
+    void enqueue(std::function<void()> t)
+    {
+        enqueueWithAio([t{std::move(t)}](AsyncIoRoot &) { t(); });
+    }
 
     /**
      * Execute work items until the queue is empty.