source/base: Add the prepare callback functionality

3 files changed, 64 insertions, 0 deletions

diff --git a/src/sdeventplus/internal/sdevent.hpp b/src/sdeventplus/internal/sdevent.hpp
index e6c420c..dfb6285 100644
--- a/src/sdeventplus/internal/sdevent.hpp
+++ b/src/sdeventplus/internal/sdevent.hpp
@@ -32,6 +32,9 @@ class SdEvent
     virtual int
         sd_event_source_set_description(sd_event_source* source,
                                         const char* description) const = 0;
+    virtual int
+        sd_event_source_set_prepare(sd_event_source* source,
+                                    sd_event_handler_t callback) const = 0;
     virtual int sd_event_source_get_pending(sd_event_source* source) const = 0;
     virtual int sd_event_source_get_priority(sd_event_source* source,
                                              int64_t* priority) const = 0;
@@ -101,6 +104,11 @@ class SdEventImpl : public SdEvent
     {
         return ::sd_event_source_set_description(source, description);
     }
+    int sd_event_source_set_prepare(sd_event_source* source,
+                                    sd_event_handler_t callback) const override
+    {
+        return ::sd_event_source_set_prepare(source, callback);
+    }
     int sd_event_source_get_pending(sd_event_source* source) const override
     {
         return ::sd_event_source_get_pending(source);
diff --git a/src/sdeventplus/source/base.cpp b/src/sdeventplus/source/base.cpp
index d99d562..d361333 100644
--- a/src/sdeventplus/source/base.cpp
+++ b/src/sdeventplus/source/base.cpp
@@ -1,4 +1,5 @@
 #include <cerrno>
+#include <cstdio>
 #include <exception>
 #include <sdeventplus/exception.hpp>
 #include <sdeventplus/internal/sdevent.hpp>
@@ -17,6 +18,30 @@ Base::~Base()
     set_enabled(SD_EVENT_OFF);
 }
 
+int Base::prepareCallback()
+{
+    try
+    {
+        prepare(*this);
+        return 0;
+    }
+    catch (const std::system_error& e)
+    {
+        fprintf(stderr, "sdeventplus: prepareCallback: %s\n", e.what());
+        return -e.code().value();
+    }
+    catch (const std::exception& e)
+    {
+        fprintf(stderr, "sdeventplus: prepareCallback: %s\n", e.what());
+        return -ENOSYS;
+    }
+    catch (...)
+    {
+        fprintf(stderr, "sdeventplus: prepareCallback: Unknown error\n");
+        return -ENOSYS;
+    }
+}
+
 const char* Base::get_description()
 {
     const char* description;
@@ -38,6 +63,28 @@ void Base::set_description(const char* description)
     }
 }
 
+static int prepare_callback(sd_event_source*, void* userdata)
+{
+    if (userdata == nullptr)
+    {
+        fprintf(stderr, "sdeventplus: prepare_callback: Missing userdata\n");
+        return -EINVAL;
+    }
+    return reinterpret_cast<Base*>(userdata)->prepareCallback();
+}
+
+void Base::set_prepare(Callback&& callback)
+{
+    int r = sdevent->sd_event_source_set_prepare(
+        source.get(), callback ? prepare_callback : nullptr);
+    if (r < 0)
+    {
+        prepare = nullptr;
+        throw SdEventError(-r, "sd_event_source_set_prepare");
+    }
+    prepare = std::move(callback);
+}
+
 int Base::get_pending()
 {
     int r = sdevent->sd_event_source_get_pending(source.get());
diff --git a/src/sdeventplus/source/base.hpp b/src/sdeventplus/source/base.hpp
index 20ab820..748f340 100644
--- a/src/sdeventplus/source/base.hpp
+++ b/src/sdeventplus/source/base.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <functional>
 #include <sdeventplus/internal/sdevent.hpp>
 #include <sdeventplus/internal/sdref.hpp>
 #include <systemd/sd-bus.h>
@@ -14,6 +15,8 @@ namespace source
 class Base
 {
   public:
+    using Callback = std::function<void(Base& source)>;
+
     virtual ~Base();
 
     // We don't want to allow any kind of slicing.
@@ -22,8 +25,11 @@ class Base
     Base(Base&& source) = delete;
     Base& operator=(Base&& source) = delete;
 
+    int prepareCallback();
+
     const char* get_description();
     void set_description(const char* description);
+    void set_prepare(Callback&& callback);
     int get_pending();
     int64_t get_priority();
     void set_priority(int64_t priority);
@@ -39,6 +45,9 @@ class Base
          internal::SdEvent* sdevent = &internal::sdevent_impl);
     Base(sd_event_source* source, std::false_type,
          internal::SdEvent* sdevent = &internal::sdevent_impl);
+
+  private:
+    Callback prepare;
 };
 
 } // namespace source