input: stream_set_blocking(): libuv impl

- Create a private libuv loop instead of re-using uv_default_loop(), to
  avoid conflict[1] with existing watcher(s) on the fd.
- Expose the global "input" fd as a getter instead of a mutable global.

[1] .deps/build/src/libuv/src/unix/core.c:833:
      uv__io_stop: Assertion `loop->watchers[w->fd] == w' failed.

src/nvim/globals.h

@@ -1217,9 +1217,6 @@ EXTERN char *ignoredp;
 // If a msgpack-rpc channel should be started over stdin/stdout
 EXTERN bool embedded_mode INIT(= false);
 
-/// TTY from which input was gathered.
-EXTERN int global_input_fd INIT(= 0);
-
 /// Used to track the status of external functions.
 /// Currently only used for iconv().
 typedef enum {

src/nvim/if_cscope.c

@@ -820,7 +820,7 @@ err_closing:
     if (execl("/bin/sh", "sh", "-c", cmd, (char *)NULL) == -1)
       PERROR(_("cs_create_connection exec failed"));
 
-    stream_set_blocking(global_input_fd, true);  //normalize stream (#2598)
+    stream_set_blocking(input_global_fd(), true);  // normalize stream (#2598)
     exit(127);
   /* NOTREACHED */
   default:      /* parent. */

src/nvim/main.c

@@ -273,13 +273,13 @@ int main(int argc, char **argv)
   if (reading_input) {
     // One of the startup commands (arguments, sourced scripts or plugins) may
     // prompt the user, so start reading from a tty now.
-    global_input_fd = fileno(stdin);
+    int fd = fileno(stdin);
     if (!params.input_isatty || params.edit_type == EDIT_STDIN) {
       // Use stderr or stdout since stdin is not a tty and/or could be used to
       // read the "-" file (eg: cat file | nvim -)
-      global_input_fd = params.err_isatty ? fileno(stderr) : fileno(stdout);
+      fd = params.err_isatty ? fileno(stderr) : fileno(stdout);
     }
-    input_start_stdin(global_input_fd);
+    input_start_stdin(fd);
   }
 
   // open terminals when opening files that start with term://

src/nvim/misc1.c

@@ -2679,6 +2679,7 @@ void preserve_exit(void)
 
   // Prevent repeated calls into this method.
   if (really_exiting) {
+    stream_set_blocking(input_global_fd(), true);  //normalize stream (#2598)
     exit(2);
   }
 
@@ -2699,7 +2700,6 @@ void preserve_exit(void)
   }
 
   ml_close_all(false);              // close all memfiles, without deleting
-  stream_set_blocking(global_input_fd, true);  //normalize stream (#2598)
 
   mch_errmsg("Vim: Finished.\n");
 

src/nvim/os/input.c

@@ -35,6 +35,7 @@ typedef enum {
 static RStream *read_stream = NULL;
 static RBuffer *read_buffer = NULL, *input_buffer = NULL;
 static bool input_eof = false;
+static int global_fd = 0;
 
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "os/input.c.generated.h"
@@ -47,12 +48,19 @@ void input_init(void)
   input_buffer = rbuffer_new(INPUT_BUFFER_SIZE + MAX_KEY_CODE_LEN);
 }
 
+/// Gets the file from which input was gathered at startup.
+int input_global_fd(void)
+{
+  return global_fd;
+}
+
 void input_start_stdin(int fd)
 {
   if (read_stream) {
     return;
   }
 
+  global_fd = fd;
   read_buffer = rbuffer_new(READ_BUFFER_SIZE);
   read_stream = rstream_new(read_cb, read_buffer, NULL);
   rstream_set_file(read_stream, fd);
@@ -62,14 +70,9 @@ void input_start_stdin(int fd)
 void input_stop_stdin(void)
 {
   if (!read_stream) {
-    // In some cases (i.e. "nvim && read") where we do not explicitly play with
-    // std{in,out,err}, some other module/library nevertheless sets the stream
-    // to non-blocking; we still must "fix" the stream (#2598) in those cases.
-    stream_set_blocking(global_input_fd, true);  // normalize stream (#2598)
     return;
   }
 
-  rstream_set_blocking(read_stream, true);  // normalize stream (#2598)
   rstream_stop(read_stream);
   rstream_free(read_stream);
   read_stream = NULL;

src/nvim/os/rstream.c

@@ -297,11 +297,6 @@ void rstream_stop(RStream *rstream)
   }
 }
 
-int rstream_set_blocking(RStream *rstream, bool blocking)
-{
-  return uv_stream_set_blocking(rstream->stream, blocking);
-}
-
 /// Returns the number of bytes ready for consumption in `rstream`
 size_t rstream_pending(RStream *rstream)
 {

src/nvim/os/stream.c

@@ -14,13 +14,17 @@
 /// @return `0` on success, or `-errno` on failure.
 int stream_set_blocking(int fd, bool blocking)
 {
-  int flags = fcntl(fd, F_GETFL, 0);
-  int err = 0;
-  if (!blocking && !(flags & O_NONBLOCK)) {
-    err = fcntl(fd, F_SETFL, flags | O_NONBLOCK);
-  } else if (blocking && (flags & O_NONBLOCK)) {
-    err = fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
-  }
-  return err == -1 ? -errno : 0;
+  // Private loop to avoid conflict with existing watcher(s):
+  //    uv__io_stop: Assertion `loop->watchers[w->fd] == w' failed.
+  uv_loop_t loop;
+  uv_pipe_t stream;
+  uv_loop_init(&loop);
+  uv_pipe_init(&loop, &stream, 0);
+  uv_pipe_open(&stream, fd);
+  int retval = uv_stream_set_blocking((uv_stream_t *)&stream, blocking);
+  uv_close((uv_handle_t *)&stream, NULL);
+  uv_run(&loop, UV_RUN_NOWAIT);  // not necessary, but couldn't hurt.
+  uv_loop_close(&loop);
+  return retval;
 }
 

src/nvim/os_unix.c

@@ -181,6 +181,7 @@ void mch_exit(int r)
   ml_close_all(TRUE);           /* remove all memfiles */
 
   event_teardown();
+  stream_set_blocking(input_global_fd(), true);  // normalize stream (#2598)
 
 #ifdef EXITFREE
   free_all_mem();