thread/*Cond: add wait_for() overload with predicate

src/lib/nfs/Blocking.hxx

@@ -60,11 +60,7 @@ public:
 private:
 	bool LockWaitFinished() noexcept {
 		std::unique_lock<Mutex> lock(mutex);
-		while (!finished)
+		return cond.wait_for(lock, timeout, [this]{ return finished; });
-			if (!cond.wait_for(lock, timeout))
-				return false;
-
-		return true;
 	}
 
 	/**

src/thread/PosixCond.hxx

@@ -105,6 +105,19 @@ public:
 
 		return wait_for(lock, timeout_us);
 	}
+
+	template<typename M, typename P>
+	bool wait_for(std::unique_lock<M> &lock,
+		      std::chrono::steady_clock::duration timeout,
+		      P &&predicate) noexcept {
+		while (!predicate()) {
+			// TODO: without wait_until(), this multiplies the timeout
+			if (!wait_for(lock, timeout))
+				return predicate();
+		}
+
+		return true;
+	}
 };
 
 #endif

src/thread/WindowsCond.hxx

@@ -70,6 +70,19 @@ public:
 						&lock.mutex()->critical_section,
 						timeout_ms);
 	}
+
+	template<typename M, typename P>
+	bool wait_for(std::unique_lock<M> &lock,
+		      std::chrono::steady_clock::duration timeout,
+		      P &&predicate) noexcept {
+		while (!predicate()) {
+			// TODO: without wait_until(), this multiplies the timeout
+			if (!wait_for(lock, timeout))
+				return predicate();
+		}
+
+		return true;
+	}
 };
 
 #endif