3 files changed, 26 insertions, 2 deletions
diff --git a/src/nvim/log.c b/src/nvim/log.c
index 3575f49e78..08b6d0483e 100644
--- a/src/nvim/log.c
+++ b/src/nvim/log.c
@@ -16,29 +16,49 @@
 
 #define USR_LOG_FILE "$HOME/.nvimlog"
 
+static uv_mutex_t mutex;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "log.c.generated.h"
 #endif
 
+void log_init(void)
+{
+  uv_mutex_init(&mutex);
+}
+
+void log_lock(void)
+{
+  uv_mutex_lock(&mutex);
+}
+
+void log_unlock(void)
+{
+  uv_mutex_unlock(&mutex);
+}
+
 bool do_log(int log_level, const char *func_name, int line_num, bool eol,
             const char* fmt, ...) FUNC_ATTR_UNUSED
 {
+  log_lock();
+  bool ret = false;
   FILE *log_file = open_log_file();
 
   if (log_file == NULL) {
-    return false;
+    goto end;
   }
 
   va_list args;
   va_start(args, fmt);
-  bool ret = v_do_log_to_file(log_file, log_level, func_name, line_num, eol,
+  ret = v_do_log_to_file(log_file, log_level, func_name, line_num, eol,
                               fmt, args);
   va_end(args);
 
   if (log_file != stderr && log_file != stdout) {
     fclose(log_file);
   }
+end:
+  log_unlock();
   return ret;
 }
 
diff --git a/src/nvim/main.c b/src/nvim/main.c
index 3e096ee190..dd2b813b1c 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -177,6 +177,7 @@ void event_teardown(void)
 /// Needed for unit tests. Must be called after `time_init()`.
 void early_init(void)
 {
+  log_init();
   fs_init();
   handle_init();
 
diff --git a/src/nvim/msgpack_rpc/channel.c b/src/nvim/msgpack_rpc/channel.c
index 45e78d6e79..34ff7c6374 100644
--- a/src/nvim/msgpack_rpc/channel.c
+++ b/src/nvim/msgpack_rpc/channel.c
@@ -825,6 +825,7 @@ static void log_server_msg(uint64_t channel_id,
   msgpack_unpack_next(&unpacked, packed->data, packed->size, NULL);
   uint64_t type = unpacked.data.via.array.ptr[0].via.u64;
   DLOGN("[msgpack-rpc] nvim -> client(%" PRIu64 ") ", channel_id);
+  log_lock();
   FILE *f = open_log_file();
   fprintf(f, type ? (type == 1 ? RES : NOT) : REQ);
   log_msg_close(f, unpacked.data);
@@ -836,6 +837,7 @@ static void log_client_msg(uint64_t channel_id,
                            msgpack_object msg)
 {
   DLOGN("[msgpack-rpc] client(%" PRIu64 ") -> nvim ", channel_id);
+  log_lock();
   FILE *f = open_log_file();
   fprintf(f, is_request ? REQ : RES);
   log_msg_close(f, msg);
@@ -847,6 +849,7 @@ static void log_msg_close(FILE *f, msgpack_object msg)
   fputc('\n', f);
   fflush(f);
   fclose(f);
+  log_unlock();
 }
 #endif