Merge pull request boostorg#765 from lakshayg/future_then

add future::then() method

Author: jszuppe

include/boost/compute/async/future.hpp

@@ -82,6 +82,21 @@ class future
         return m_event;
     }
 
+    #if defined(BOOST_COMPUTE_CL_VERSION_1_1) || defined(BOOST_COMPUTE_DOXYGEN_INVOKED)
+    /// Invokes a generic callback function once the future is ready.
+    ///
+    /// The function specified by callback must be invokable with zero arguments.
+    ///
+    /// \see_opencl_ref{clSetEventCallback}
+    /// \opencl_version_warning{1,1}
+    template<class Function>
+    future& then(Function callback)
+    {
+        m_event.set_callback(callback);
+        return *this;
+    }
+    #endif // BOOST_COMPUTE_CL_VERSION_1_1
+
 private:
     T m_result;
     event m_event;
@@ -149,6 +164,21 @@ class future<void>
         return m_event;
     }
 
+    #if defined(BOOST_COMPUTE_CL_VERSION_1_1) || defined(BOOST_COMPUTE_DOXYGEN_INVOKED)
+    /// Invokes a generic callback function once the future is ready.
+    ///
+    /// The function specified by callback must be invokable with zero arguments.
+    ///
+    /// \see_opencl_ref{clSetEventCallback}
+    /// \opencl_version_warning{1,1}
+    template<class Function>
+    future<void> &then(Function callback)
+    {
+        m_event.set_callback(callback);
+        return *this;
+    }
+    #endif // BOOST_COMPUTE_CL_VERSION_1_1
+
 private:
     event m_event;
 };

test/test_event.cpp

@@ -18,6 +18,7 @@
 #include <future>
 #endif // BOOST_COMPUTE_USE_CPP11
 
+#include <boost/compute/async/future.hpp>
 #include <boost/compute/event.hpp>
 
 #include "context_setup.hpp"
@@ -85,6 +86,28 @@ BOOST_AUTO_TEST_CASE(lambda_callback)
     BOOST_CHECK_EQUAL(lambda_invoked, true);
 }
 
+BOOST_AUTO_TEST_CASE(future_then_callback)
+{
+    REQUIRES_OPENCL_VERSION(1,2);
+
+    bool callback_invoked = false;
+
+    boost::compute::future<void> future(queue.enqueue_marker());
+    future.then([&](){
+        std::lock_guard<std::mutex> lock(callback_mutex);
+        callback_invoked = true;
+        callback_condition_variable.notify_one();
+    });
+    future.wait();
+
+    // wait up to one second for the callback to be executed
+    std::unique_lock<std::mutex> lock(callback_mutex);
+    callback_condition_variable.wait_for(
+        lock, std::chrono::seconds(1), [&](){ return callback_invoked; }
+    );
+    BOOST_CHECK_EQUAL(callback_invoked, true);
+}
+
 void BOOST_COMPUTE_CL_CALLBACK
 event_promise_fulfiller_callback(cl_event event, cl_int status, void *user_data)
 {