4 files changed, 62 insertions, 5 deletions

diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index a06e9fe542..bcac32a252 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -979,6 +979,8 @@ EXTERN const char bot_top_msg[] INIT(= N_("search hit BOTTOM, continuing at TOP"
 EXTERN const char line_msg[] INIT(= N_(" line "));
 
 EXTERN FILE *time_fd INIT(= NULL);  // where to write startup timing
+#define STARTUP_TIME_BUF_SIZE 8192
+EXTERN char *startuptime_buf INIT(= NULL); // --startuptime buffer
 
 // Some compilers warn for not using a return value, but in some situations we
 // can't do anything useful with the value.  Assign to this variable to avoid
diff --git a/src/nvim/main.c b/src/nvim/main.c
index f858313682..f2893dc9e3 100644
--- a/src/nvim/main.c
+++ b/src/nvim/main.c
@@ -399,6 +399,7 @@ int main(int argc, char **argv)
   }
 
   if (ui_client_channel_id) {
+    time_finish();
     ui_client_run(remote_ui);  // NORETURN
   }
   assert(!ui_client_channel_id && !use_builtin_ui);
@@ -695,6 +696,9 @@ void getout(int exitval)
   assert(!ui_client_channel_id);
   exiting = true;
 
+  // make sure startuptimes have been flushed
+  time_finish();
+
   // On error during Ex mode, exit with a non-zero code.
   // POSIX requires this, although it's not 100% clear from the standard.
   if (exmode_active) {
@@ -1495,9 +1499,16 @@ static void init_params(mparm_T *paramp, int argc, char **argv)
 /// Initialize global startuptime file if "--startuptime" passed as an argument.
 static void init_startuptime(mparm_T *paramp)
 {
+  bool is_embed = false;
+  for (int i = 1; i < paramp->argc - 1; i++) {
+    if (STRICMP(paramp->argv[i], "--embed") == 0) {
+      is_embed = true;
+      break;
+    }
+  }
   for (int i = 1; i < paramp->argc - 1; i++) {
     if (STRICMP(paramp->argv[i], "--startuptime") == 0) {
-      time_fd = fopen(paramp->argv[i + 1], "a");
+      time_init(paramp->argv[i + 1], is_embed ? "Embedded" : "Primary/TUI");
       time_start("--- NVIM STARTING ---");
       break;
     }
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 9966e6129c..8b6ef62873 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1451,9 +1451,7 @@ static int normal_check(VimState *state)
     // has been done, close any file for startup messages.
     if (time_fd != NULL) {
       TIME_MSG("first screen update");
-      TIME_MSG("--- NVIM STARTED ---");
-      fclose(time_fd);
-      time_fd = NULL;
+      time_finish();
     }
     // After the first screen update may start triggering WinScrolled
     // autocmd events.  Store all the scroll positions and sizes now.
diff --git a/src/nvim/profile.c b/src/nvim/profile.c
index f7776ef74f..84b58de4a3 100644
--- a/src/nvim/profile.c
+++ b/src/nvim/profile.c
@@ -907,7 +907,7 @@ void time_start(const char *message)
   // initialize the global variables
   g_prev_time = g_start_time = profile_start();
 
-  fprintf(time_fd, "\n\ntimes in msec\n");
+  fprintf(time_fd, "\ntimes in msec\n");
   fprintf(time_fd, " clock   self+sourced   self:  sourced script\n");
   fprintf(time_fd, " clock   elapsed:              other lines\n\n");
 
@@ -944,3 +944,49 @@ void time_msg(const char *mesg, const proftime_T *start)
   g_prev_time = now;
   fprintf(time_fd, ": %s\n", mesg);
 }
+
+/// Initializes the time time_fd stream used to write startup times
+///
+/// @param startup_time_file the startuptime report file path
+/// @param process_name the name of the current process to write in the report.
+void time_init(const char *startup_time_file, const char *process_name)
+{
+  time_fd = fopen(startup_time_file, "a");
+  if (time_fd == NULL) {
+    semsg(_(e_notopen), startup_time_file);
+    return;
+  }
+  startuptime_buf = xmalloc(sizeof(char) * (STARTUP_TIME_BUF_SIZE + 1));
+  // The startuptime file is (potentially) written by multiple nvim processes concurrently. So
+  // startuptime info is buffered, and flushed to disk only after startup completed. To achieve that
+  // we set a buffer big enough to store all startup times. The `_IOFBF` mode ensures the buffer is
+  // not auto-flushed ("controlled buffering").
+  // The times are flushed to disk manually when "time_finish" is called.
+  int r = setvbuf(time_fd, startuptime_buf, _IOFBF, STARTUP_TIME_BUF_SIZE + 1);
+  if (r != 0) {
+    xfree(startuptime_buf);
+    fclose(time_fd);
+    time_fd = NULL;
+    // Might as well ELOG also I guess.
+    ELOG("time_init: setvbuf failed: %d %s", r, uv_err_name(r));
+    semsg("time_init: setvbuf failed: %d %s", r, uv_err_name(r));
+    return;
+  }
+  fprintf(time_fd, "--- Startup times for process: %s ---\n", process_name);
+}
+
+/// Flushes the startuptimes to disk for the current process
+void time_finish(void)
+{
+  if (time_fd == NULL) {
+    return;
+  }
+  assert(startuptime_buf != NULL);
+  TIME_MSG("--- NVIM STARTED ---\n");
+
+  // flush buffer to disk
+  fclose(time_fd);
+  time_fd = NULL;
+
+  XFREE_CLEAR(startuptime_buf);
+}