[ADD/WIP] Push all the Janet changes

This is still unstable(and I still need to design/document the exposed
API)! Do(n't) go and use it!

src/Extensions/PushEvents.c

@@ -0,0 +1,89 @@
+#ifdef JANET
+
+#include "Extensions/Internal.h"
+
+typedef struct ExtensionEventReply {
+    pthread_mutex_t lock;
+    pthread_cond_t cond;
+
+    HashMap *obj;
+
+    Extension *ext;
+    bool reply, ack;
+} ExtensionEventReply;
+
+static void
+OnEventResponse(JanetEVGenericMessage msg)
+{
+    ExtensionEventReply *reply = msg.argp;
+    Extension *ext = reply->ext;
+    Janet args[1] = {
+        JsonToJanet(reply->obj),
+    };
+    Janet ret;
+
+    if (TryCall(ext, "on-event", 1, args, &ret))
+    {
+        pthread_mutex_lock(&reply->lock);
+        reply->ack = true;
+        reply->reply = janet_truthy(ret);
+        pthread_cond_signal(&reply->cond);
+        pthread_mutex_unlock(&reply->lock);
+        return;
+    }
+    pthread_mutex_lock(&reply->lock);
+    reply->ack = true;
+    reply->reply = false;
+    pthread_cond_signal(&reply->cond);
+    pthread_mutex_unlock(&reply->lock);
+}
+bool
+ExtensionPushEvent(Extensions *ctx, HashMap *obj)
+{
+    bool veto = false;
+    size_t i;
+
+    char *key;
+    Extension *val;
+    if (!ctx || !obj)
+    {
+        return false;
+    }
+
+    pthread_mutex_lock(&ctx->mtx);
+    for (i = 0; IterateReentrant(ctx->extensions, key, val, i); )
+    {
+        ExtensionEventReply *reply = Malloc(sizeof(*reply));
+        JanetEVGenericMessage msg = {
+            /* We except a veto boolean. */
+            .tag = JANET_STANZA_PUSH,
+        };
+
+        pthread_mutex_init(&reply->lock, NULL);
+        pthread_cond_init(&reply->cond, NULL);
+        reply->ext = val;
+        reply->reply = false;
+        reply->ack = false;
+        reply->obj = obj;
+        msg.argp = reply;
+
+        janet_ev_post_event(val->vm, OnEventResponse, msg);
+        pthread_mutex_lock(&reply->lock);
+        while (!reply->ack)
+        {
+            pthread_cond_wait(&reply->cond, &reply->lock);
+        }
+        pthread_mutex_unlock(&reply->lock);
+        pthread_mutex_destroy(&reply->lock);
+        pthread_cond_destroy(&reply->cond);
+        if (reply->reply)
+        {
+            veto = true;
+        }
+        Free(reply);
+    }
+    pthread_mutex_unlock(&ctx->mtx);
+
+    return veto;
+}
+#endif