From 297c2e5b17519a597202dfb142217f9eeb545995 Mon Sep 17 00:00:00 2001
From: Ilya Averyanov <av@rubybox.dev>
Date: Tue, 9 Apr 2024 09:25:49 +0300
Subject: [PATCH] fix: add lock for enif_send synchronization

---
 c_src/main.c      | 23 ++++++++++++++---------
 c_src/resources.c |  8 ++++++--
 c_src/resources.h |  4 +++-
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/c_src/main.c b/c_src/main.c
index 090ff70..08372d8 100644
--- a/c_src/main.c
+++ b/c_src/main.c
@@ -78,17 +78,17 @@ erlfdb_future_cb(FDBFuture* fdb_future, void* data)
     ERL_NIF_TERM msg;
     bool cancelled;
 
-
-    enif_mutex_lock(future->lock);
+    enif_mutex_lock(future->cancel_lock);
     cancelled = future->cancelled;
-    enif_mutex_unlock(future->lock);
+    enif_mutex_unlock(future->cancel_lock);
 
     if(!cancelled) {
+        enif_mutex_lock(future->msg_lock);
         msg = T2(future->msg_env, future->msg_ref, ATOM_ready);
         enif_send(NULL, &(future->pid), future->msg_env, msg);
+        enif_mutex_unlock(future->msg_lock);
     }
 
-
     // We're now done with this future which means we need
     // to release our handle to it. See erlfdb_create_future
     // for more on why this happens here.
@@ -107,14 +107,19 @@ erlfdb_create_future(ErlNifEnv* env, FDBFuture* future, ErlFDBFutureGetter gette
     ERL_NIF_TERM ret;
     fdb_error_t err;
 
+    // TODO: check results of each operation.
+    // TODO: return error if any operation fails and clean previously allocated resources.
+
     f = enif_alloc_resource(ErlFDBFutureRes, sizeof(ErlFDBFuture));
     f->future = future;
     f->fgetter = getter;
     enif_self(env, &(f->pid));
     f->msg_env = enif_alloc_env();
     f->msg_ref = enif_make_copy(f->msg_env, ref);
-    f->lock = enif_mutex_create("fdb:future_lock");
+    f->msg_lock = enif_mutex_create("fdb:future_msg_lock");
+
     f->cancelled = false;
+    f->cancel_lock = enif_mutex_create("fdb:future_cancel_lock");
 
     // This resource reference counting dance is a bit
     // awkward as erlfdb_future_cb can be called both
@@ -557,10 +562,10 @@ erlfdb_future_cancel(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
     }
     future = (ErlFDBFuture*) res;
 
-    enif_mutex_lock(future->lock);
+    enif_mutex_lock(future->cancel_lock);
 
     future->cancelled = true;
-    enif_mutex_unlock(future->lock);
+    enif_mutex_unlock(future->cancel_lock);
 
     fdb_future_cancel(future->future);
 
@@ -589,11 +594,11 @@ erlfdb_future_silence(ErlNifEnv* env, int argc, const ERL_NIF_TERM argv[])
     }
     future = (ErlFDBFuture*) res;
 
-    enif_mutex_lock(future->lock);
+    enif_mutex_lock(future->cancel_lock);
 
     future->cancelled = true;
 
-    enif_mutex_unlock(future->lock);
+    enif_mutex_unlock(future->cancel_lock);
 
     return ATOM_ok;
 }
diff --git a/c_src/resources.c b/c_src/resources.c
index 7c4e392..bc0bebd 100644
--- a/c_src/resources.c
+++ b/c_src/resources.c
@@ -87,8 +87,12 @@ erlfdb_future_dtor(ErlNifEnv* env, void* obj)
         enif_free_env(f->msg_env);
     }
 
-    if(f->lock != NULL) {
-        enif_mutex_destroy(f->lock);
+    if(f->cancel_lock != NULL) {
+        enif_mutex_destroy(f->cancel_lock);
+    }
+
+    if(f->msg_lock != NULL) {
+        enif_mutex_destroy(f->msg_lock);
     }
 }
 
diff --git a/c_src/resources.h b/c_src/resources.h
index 265f725..be02c7f 100644
--- a/c_src/resources.h
+++ b/c_src/resources.h
@@ -35,8 +35,10 @@ struct _ErlFDBFuture
     ErlNifPid pid;
     ErlNifEnv* msg_env;
     ERL_NIF_TERM msg_ref;
-    ErlNifMutex* lock;
+    ErlNifMutex* msg_lock;
+
     bool cancelled;
+    ErlNifMutex* cancel_lock;
 };