[esnacc-dev] [PATCH 2/2] cxx-lib/asn-buf: Stream buffer monitor

[Aaron Conole]

Introduce a mechanism for monitoring and calling back stream buffer
objects.  This is useful for building busy-wait loops, which can perform
tasks as interleaved callbacks.

Signed-off-by: Aaron Conole <aconole at bytheb.org>
---
 cxx-lib/inc/asn-buf.h | 99 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)

diff --git a/cxx-lib/inc/asn-buf.h b/cxx-lib/inc/asn-buf.h
index d316ba9..872484b 100644
--- a/cxx-lib/inc/asn-buf.h
+++ b/cxx-lib/inc/asn-buf.h
@@ -7,9 +7,11 @@
 #pragma warning(push,3)
 #endif
 
+#include <algorithm>
 #include <deque>
 #include <fstream>
 #include <list>
+#include <map>
 #include <ostream>
 #include <sstream>
 #include <streambuf>
@@ -413,6 +415,103 @@ private:
 
 };
 
+
+class StreambufCallback
+{
+public:
+    enum Streambuf_CB_RESULT {
+        CB_NONE,
+        CB_DROP_STREAM
+    };
+    
+    enum Streambuf_CB_STATUS {
+        CB_READ_OK,
+        CB_WRITE_OK,
+        CB_OPENED,
+        CB_CLOSED
+    };
+            
+    StreambufCallback(){}
+    virtual ~StreambufCallback(){}
+    virtual Streambuf_CB_RESULT callback(Streambuf_CB_STATUS status,
+                                         std::streambuf *stream) = 0;
+};
+
+class StreambufMonitor
+{
+public:
+    typedef std::map<std::streambuf*,StreambufCallback&> callbackMap;
+
+private:
+    callbackMap                 callbacks;
+    std::list<std::streambuf*>  toDrop;
+
+    static void check_buffer(callbackMap::value_type t,
+                             std::list<std::streambuf*> &StreamDropList)
+    {
+        std::streambuf *Stream = t.first;
+        std::streamsize Bytes = Stream->in_avail();
+        StreambufCallback::Streambuf_CB_RESULT result =
+            StreambufCallback::CB_NONE;
+
+        if (Bytes == -1) {
+            result = (t.second).callback(StreambufCallback::CB_CLOSED, Stream);
+        } else if (Bytes > 0) {
+            result = (t.second).callback(StreambufCallback::CB_READ_OK,
+                                         Stream);
+        }
+
+        if (result == StreambufCallback::CB_DROP_STREAM) {
+            StreamDropList.push_back(Stream);
+        }
+    }
+
+    struct buffer_checker
+    {
+        StreambufMonitor *Mon;
+        void operator()(callbackMap::value_type t)
+        {
+            StreambufMonitor::check_buffer(t, Mon->toDrop);
+        }
+    };
+            
+public:
+    StreambufMonitor() {}
+    ~StreambufMonitor() {}
+
+    /**
+     * Adds a streambuf to be monitored, with a specific callback instance. */
+    bool push(std::streambuf *Stream, StreambufCallback &CB, bool callOpen)
+    {
+        if (callOpen) {
+            StreambufCallback::Streambuf_CB_RESULT result =
+                CB.callback(StreambufCallback::CB_OPENED, Stream);
+            if (result == StreambufCallback::CB_DROP_STREAM)
+                return false;
+        }
+        callbacks.insert(
+            std::pair<std::streambuf*,StreambufCallback&>(Stream,CB));
+        return true;
+    }
+
+    /**
+     * Removes a streambuf from the monitor. */
+    bool pop(std::streambuf *Stream)
+    {
+        if (callbacks.erase(Stream))
+            return true;
+        return false;
+    }
+
+    void operator()()
+    {
+        buffer_checker bc;
+        bc.Mon = this;
+        std::for_each(callbacks.begin(), callbacks.end(), bc);
+        toDrop.clear();
+    }
+};
+
 } // end namespace SNACC
 
 SNACCDLL_API void sortSet(std::list<SNACC::AsnBuf> &bufList);
-- 
2.5.5