From a3c18e72f5804051c5111fea5f4fca488fa088ca Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sat, 4 Jan 2020 19:48:15 +0100
Subject: [PATCH] fdm: add support for hooks

Hooks are functions executed just before going into a poll(). Or just
after executing all FD handlers, if you like.
---
 fdm.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 fdm.h |  4 ++++
 2 files changed, 53 insertions(+)

diff --git a/fdm.c b/fdm.c
index 4592a9e8..9d14dca8 100644
--- a/fdm.c
+++ b/fdm.c
@@ -21,11 +21,17 @@ struct handler {
     bool deleted;
 };
 
+struct hook {
+    fdm_hook_t callback;
+    void *callback_data;
+};
+
 struct fdm {
     int epoll_fd;
     bool is_polling;
     tll(struct handler *) fds;
     tll(struct handler *) deferred_delete;
+    tll(struct hook) hooks;
 };
 
 struct fdm *
@@ -43,6 +49,7 @@ fdm_init(void)
         .is_polling = false,
         .fds = tll_init(),
         .deferred_delete = tll_init(),
+        .hooks = tll_init(),
     };
     return fdm;
 }
@@ -56,11 +63,16 @@ fdm_destroy(struct fdm *fdm)
     if (tll_length(fdm->fds) > 0)
         LOG_WARN("FD list not empty");
 
+    if (tll_length(fdm->hooks) > 0)
+        LOG_WARN("hook list not empty");
+
     assert(tll_length(fdm->fds) == 0);
     assert(tll_length(fdm->deferred_delete) == 0);
+    assert(tll_length(fdm->hooks) == 0);
 
     tll_free(fdm->fds);
     tll_free(fdm->deferred_delete);
+    tll_free(fdm->hooks);
     close(fdm->epoll_fd);
     free(fdm);
 }
@@ -195,6 +207,37 @@ fdm_event_del(struct fdm *fdm, int fd, int events)
     return false;
 }
 
+bool
+fdm_hook_add(struct fdm *fdm, fdm_hook_t hook, void *data)
+{
+#if defined(_DEBUG)
+    tll_foreach(fdm->hooks, it) {
+        if (it->item.callback == hook) {
+            LOG_ERR("hook=%p already registered", hook);
+            return false;
+        }
+    }
+#endif
+
+    tll_push_back(fdm->hooks, ((struct hook){hook, data}));
+    return true;
+}
+
+bool
+fdm_hook_del(struct fdm *fdm, fdm_hook_t hook)
+{
+    tll_foreach(fdm->hooks, it) {
+        if (it->item.callback != hook)
+            continue;
+
+        tll_remove(fdm->hooks, it);
+        return true;
+    }
+
+    LOG_WARN("hook=%p not registered, hook", hook);
+    return false;
+}
+
 bool
 fdm_poll(struct fdm *fdm)
 {
@@ -204,6 +247,12 @@ fdm_poll(struct fdm *fdm)
         return false;
     }
 
+    tll_foreach(fdm->hooks, it) {
+        LOG_DBG("executing hook %p(fdm=%p, data=%p)",
+                it->item.callback, fdm, it->item.callback_data);
+        it->item.callback(fdm, it->item.callback_data);
+    }
+
     struct epoll_event events[tll_length(fdm->fds)];
 
     int r = epoll_wait(fdm->epoll_fd, events, tll_length(fdm->fds), -1);
diff --git a/fdm.h b/fdm.h
index 62d73ded..62f7616f 100644
--- a/fdm.h
+++ b/fdm.h
@@ -5,6 +5,7 @@
 struct fdm;
 
 typedef bool (*fdm_handler_t)(struct fdm *fdm, int fd, int events, void *data);
+typedef void (*fdm_hook_t)(struct fdm *fdm, void *data);
 
 struct fdm *fdm_init(void);
 void fdm_destroy(struct fdm *fdm);
@@ -16,4 +17,7 @@ bool fdm_del_no_close(struct fdm *fdm, int fd);
 bool fdm_event_add(struct fdm *fdm, int fd, int events);
 bool fdm_event_del(struct fdm *fdm, int fd, int events);
 
+bool fdm_hook_add(struct fdm *fdm, fdm_hook_t hook, void *data);
+bool fdm_hook_del(struct fdm *fdm, fdm_hook_t hook);
+
 bool fdm_poll(struct fdm *fdm);