input/Stream: remove attribute "cond", replace with handler interface

This adds a bit of overhead, but also adds flexibility to the API,
because arbitrary triggers may be invoked from that virtual method
implementation, not just Cond::signal().

The motivation for this is to make the handlers more dynamic, for the
upcoming buffering class utilizing ProxyInputStream.

src/input/InputStream.cxx

@@ -19,8 +19,8 @@
 
 #include "config.h"
 #include "InputStream.hxx"
+#include "Handler.hxx"
 #include "tag/Tag.hxx"
-#include "thread/Cond.hxx"
 #include "util/StringCompare.hxx"
 
 #include <stdexcept>
@@ -47,26 +47,8 @@ InputStream::SetReady() noexcept
 	assert(!ready);
 
 	ready = true;
-	cond.broadcast();
-}
 
-void
-InputStream::WaitReady() noexcept
-{
-	while (true) {
-		Update();
-		if (ready)
-			break;
-
-		cond.wait(mutex);
-	}
-}
-
-void
-InputStream::LockWaitReady() noexcept
-{
-	const std::lock_guard<Mutex> protect(mutex);
-	WaitReady();
+	InvokeOnReady();
 }
 
 /**
@@ -177,3 +159,17 @@ InputStream::LockIsEOF() noexcept
 	const std::lock_guard<Mutex> protect(mutex);
 	return IsEOF();
 }
+
+void
+InputStream::InvokeOnReady() noexcept
+{
+	if (handler != nullptr)
+		handler->OnInputStreamReady();
+}
+
+void
+InputStream::InvokeOnAvailable() noexcept
+{
+	if (handler != nullptr)
+		handler->OnInputStreamAvailable();
+}