fix(script): Receiving multiple lines rapidly only displays first line (#3119)

Fixes #3117

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 ### Fixed
+- `custom/script`: When a script with `tail = true` received multiple lines quickly, only the first would get displayed ([`#3117`](https://github.com/polybar/polybar/issues/3117), [`#3119`](https://github.com/polybar/polybar/pull/3119)) by [@Isak05](https://github.com/Isak05)
 -  Token min-length calculations would behave differently when non-ASCII characters appear in the token ([`#3074`](https://github.com/polybar/polybar/issues/3074), [`#3087`](https://github.com/polybar/polybar/pull/3087)) by [@nklloyd](https://github.com/nklloyd)
 -  i3: Fix duplicated rendering for non-full-width bars ([`#3091`](https://github.com/polybar/polybar/pull/3091), [`#3060`](https://github.com/polybar/polybar/issues/3060))
 - `internal/backlight`: Module could display the literal `%percentage%` token if the backlight reports a value of 0 at startup ([`#3081`](https://github.com/polybar/polybar/pull/3081)) by [@unclechu](https://github.com/unclechu)

include/modules/meta/base.inl

@@ -119,7 +119,7 @@ namespace modules {
 
   template <typename Impl>
   string module<Impl>::contents() {
-    if (m_changed) {
+    if (m_changed.exchange(false)) {
       m_log.info("%s: Rebuilding cache", name());
       m_cache = CAST_MOD(Impl)->get_output();
       // Make sure builder is really empty
@@ -129,7 +129,6 @@ namespace modules {
         m_builder->control(tags::controltag::R);
         m_cache += m_builder->flush();
       }
-      m_changed = false;
     }
     return m_cache;
   }

include/utils/command.hpp

@@ -92,6 +92,7 @@ class command<output_policy::REDIRECTED> : private command<output_policy::IGNORE
 
   void tail(std::function<void(string)> cb);
   string readline();
+  bool wait_for_data(int timeout_ms);
 
   int get_stdout(int c);
   int get_stdin(int c);

src/adapters/script_runner.cpp

@@ -155,7 +155,7 @@ script_runner::interval script_runner::run_tail() {
   assert(fd != -1);
 
   while (!m_stopping && cmd.is_running() && !io_util::poll(fd, POLLHUP, 0)) {
-    if (io_util::poll_read(fd, 250)) {
+    if (cmd.wait_for_data(250)) {
       auto changed = set_output(cmd.readline());
 
       if (changed) {

src/utils/command.cpp

@@ -201,6 +201,14 @@ string command<output_policy::REDIRECTED>::readline() {
   return s;
 }
 
+/**
+ * Wait until there is data in the output stream or until timeout_ms milliseconds
+ */
+bool command<output_policy::REDIRECTED>::wait_for_data(int timeout_ms) {
+  return (m_stdout_reader && m_stdout_reader->rdbuf()->in_avail() > 0) ||
+          io_util::poll_read(get_stdout(PIPE_READ), timeout_ms);
+}
+
 /**
  * Get command output channel
  */