script: Fix concurrency issues (#2518)

Fixes #1978

* Move tail and non-tail handler to method

Defining them in the constructor is ugly.

* script: Iterate over defined actions instead of fixed list

* Separate running logic and lock m_output

* Include POLYBAR_FLAGS in linker flags

* Stop using m_prev in script_runner

* Join module threads in stop function

Joining in the destructor may lead to UB because the subclass is already
deconstructed but the threads may still require it to be around (e.g.
for calling any functions on the instance)

* Cleanup script module

* Update changelog

* Remove AfterReturn class

* Remove m_stopping from script module

* Fix polybar not reading the entire line from child process.

For every `readline` call we created a new fd_streambuf. This means once
`readline` returns, the streambuf is destructed and and pending data in
its temporary buffer discarded and we never actually read it.

* Remove unused includes

src/adapters/script_runner.cpp

@@ -0,0 +1,154 @@
+#include "adapters/script_runner.hpp"
+
+#include <cassert>
+#include <functional>
+
+#include "modules/meta/base.hpp"
+#include "utils/command.hpp"
+#include "utils/io.hpp"
+#include "utils/scope.hpp"
+#include "utils/string.hpp"
+
+POLYBAR_NS
+
+script_runner::script_runner(std::function<void(void)> on_update, const string& exec, const string& exec_if, bool tail,
+    interval interval, const vector<pair<string, string>>& env)
+    : m_log(logger::make())
+    , m_on_update(on_update)
+    , m_exec(exec)
+    , m_exec_if(exec_if)
+    , m_tail(tail)
+    , m_interval(interval)
+    , m_env(env) {}
+
+/**
+ * Check if defined condition is met
+ */
+bool script_runner::check_condition() const {
+  if (m_exec_if.empty()) {
+    return true;
+  }
+
+  auto exec_if_cmd = command_util::make_command<output_policy::IGNORED>(m_exec_if);
+  return exec_if_cmd->exec(true) == 0;
+}
+
+/**
+ * Process mutex wrapped script handler
+ */
+script_runner::interval script_runner::process() {
+  if (m_tail) {
+    return run_tail();
+  } else {
+    return run();
+  }
+}
+
+void script_runner::clear_output() {
+  set_output("");
+}
+
+void script_runner::stop() {
+  m_stopping = true;
+}
+
+int script_runner::get_pid() const {
+  return m_pid;
+}
+
+int script_runner::get_counter() const {
+  return m_counter;
+}
+
+string script_runner::get_output() {
+  std::lock_guard<std::mutex> guard(m_output_lock);
+  return m_output;
+}
+
+bool script_runner::is_stopping() const {
+  return m_stopping;
+}
+
+/**
+ * Updates the current output.
+ *
+ * Returns true if the output changed.
+ */
+bool script_runner::set_output(const string&& new_output) {
+  std::lock_guard<std::mutex> guard(m_output_lock);
+
+  if (m_output != new_output) {
+    m_output = std::move(new_output);
+    m_on_update();
+    return true;
+  }
+
+  return false;
+}
+
+script_runner::interval script_runner::run() {
+  auto exec = string_util::replace_all(m_exec, "%counter%", to_string(++m_counter));
+  m_log.info("script_runner: Invoking shell command: \"%s\"", exec);
+  auto cmd = command_util::make_command<output_policy::REDIRECTED>(exec);
+
+  try {
+    cmd->exec(true, m_env);
+  } catch (const exception& err) {
+    m_log.err("script_runner: %s", err.what());
+    throw modules::module_error("Failed to execute command, stopping module...");
+  }
+
+  int status = cmd->get_exit_status();
+  int fd = cmd->get_stdout(PIPE_READ);
+  assert(fd != -1);
+  bool changed = io_util::poll_read(fd) && set_output(cmd->readline());
+
+  if (!changed && status != 0) {
+    clear_output();
+  }
+
+  if (status == 0) {
+    return m_interval;
+  } else {
+    return std::max(m_interval, interval{1s});
+  }
+}
+
+script_runner::interval script_runner::run_tail() {
+  auto exec = string_util::replace_all(m_exec, "%counter%", to_string(++m_counter));
+  m_log.info("script_runner: Invoking shell command: \"%s\"", exec);
+  auto cmd = command_util::make_command<output_policy::REDIRECTED>(exec);
+
+  try {
+    cmd->exec(false, m_env);
+  } catch (const exception& err) {
+    throw modules::module_error("Failed to execute command: " + string(err.what()));
+  }
+
+  auto pid_guard = scope_util::make_exit_handler([this]() { m_pid = -1; });
+  m_pid = cmd->get_pid();
+
+  int fd = cmd->get_stdout(PIPE_READ);
+  assert(fd != -1);
+
+  while (!m_stopping && cmd->is_running() && !io_util::poll(fd, POLLHUP, 0)) {
+    if (io_util::poll_read(fd, 25)) {
+      set_output(cmd->readline());
+    }
+  }
+
+  if (m_stopping) {
+    cmd->terminate();
+    return 0s;
+  }
+
+  bool exit_status = cmd->wait();
+
+  if (exit_status == 0) {
+    return m_interval;
+  } else {
+    return std::max(m_interval, interval{1s});
+  }
+}
+
+POLYBAR_NS_END