fix(pulse): Hanging during connection setup (#2709)

If context_state_callback is called before we call
pa_threaded_mainloop_wait in the main thread, the signal is lost and we
wait forever.

Fixes #2707
Ref #2699
Ref #2697

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - ipc: Polybar failing to open IPC channel after another user already ran polybar, if `XDG_RUNTIME_DIR` is not set ([`#2683`](https://github.com/polybar/polybar/issues/2683), [`#2684`](https://github.com/polybar/polybar/pull/2684))
 - No overlines/underlines being drawn when using offsets ([`#2685`](https://github.com/polybar/polybar/pull/2685))
 - Update struts (`_NET_WM_STRUT_PARTIAL`) when hiding the bar ([`#2702`](https://github.com/polybar/polybar/pull/2702))
+- `internal/pulseaudio`: Hanging during startup ([`#2707`](https://github.com/polybar/polybar/issues/2707), [`#2709`](https://github.com/polybar/polybar/pull/2709))
 
 ## [3.6.2] - 2022-04-03
 ### Fixed

include/adapters/pulseaudio.hpp

@@ -2,6 +2,7 @@
 
 #include <pulse/pulseaudio.h>
 
+#include <atomic>
 #include <queue>
 
 #include "common.hpp"
@@ -58,6 +59,11 @@ class pulseaudio {
 
   const logger& m_log;
 
+  /**
+   * Has context_state_callback signalled the mainloop during connection.
+   */
+  std::atomic_bool m_state_callback_signal{false};
+
   // used for temporary callback results
   int success{0};
   pa_cvolume cv{};

src/adapters/pulseaudio.cpp

@@ -24,6 +24,8 @@ pulseaudio::pulseaudio(const logger& logger, string&& sink_name, bool max_volume
 
   pa_context_set_state_callback(m_context, context_state_callback, this);
 
+  m_state_callback_signal = false;
+
   if (pa_context_connect(m_context, nullptr, PA_CONTEXT_NOFLAGS, nullptr) < 0) {
     pa_context_disconnect(m_context);
     pa_context_unref(m_context);
@@ -42,7 +44,17 @@ pulseaudio::pulseaudio(const logger& logger, string&& sink_name, bool max_volume
 
   m_log.trace("pulseaudio: started mainloop");
 
+  /*
+   * Only wait for signal from the context state callback, if it has not
+   * already signalled the mainloop since pa_context_connect was called,
+   * otherwise, we would wait forever.
+   *
+   * The while loop ensures spurious wakeups are handled.
+   */
+  while (!m_state_callback_signal) {
     pa_threaded_mainloop_wait(m_mainloop);
+  }
+
   if (pa_context_get_state(m_context) != PA_CONTEXT_READY) {
     pa_threaded_mainloop_unlock(m_mainloop);
     pa_threaded_mainloop_stop(m_mainloop);
@@ -310,6 +322,7 @@ void pulseaudio::context_state_callback(pa_context* context, void* userdata) {
     case PA_CONTEXT_READY:
     case PA_CONTEXT_TERMINATED:
     case PA_CONTEXT_FAILED:
+      This->m_state_callback_signal = true;
       pa_threaded_mainloop_signal(This->m_mainloop, 0);
       break;