Move the pid_running() function to common utils

We're going to need this for our watchdog.

src/common/utils.cpp

@@ -48,6 +48,24 @@ bool set_realtime_priority(bool sched_fifo, int priority) {
                               &params) == 0;
 }
 
+bool pid_running(pid_t pid) {
+    // With regular individually hosted plugins we can simply check whether the
+    // process is still running, however Boost.Process does not allow you to do
+    // the same thing for a process that's not a direct child if this process.
+    // When using plugin groups we'll have to manually check whether the PID
+    // returned by the group host process is still active. We sadly can't use
+    // `kill()` for this as that provides no way to distinguish between active
+    // processes and zombies, and a terminated group host process will always be
+    // left as a zombie process. If the process is active, then
+    // `/proc/<pid>/{cwd,exe,root}` will be valid symlinks.
+    try {
+        fs::canonical("/proc/" + std::to_string(pid) + "/exe");
+        return true;
+    } catch (const fs::filesystem_error&) {
+        return false;
+    }
+}
+
 ScopedFlushToZero::ScopedFlushToZero() {
     old_ftz_mode = _MM_GET_FLUSH_ZERO_MODE();
     _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON);

src/common/utils.h

@@ -84,6 +84,12 @@ std::optional<int> get_realtime_priority();
  */
 bool set_realtime_priority(bool sched_fifo, int priority = 5);
 
+/**
+ * Check whether a process with the given PID is still active (and not a
+ * zombie).
+ */
+bool pid_running(pid_t pid);
+
 /**
  * A RAII wrapper that will temporarily enable the FTZ flag so that denormals
  * are automatically flushed to zero, returning to whatever the flag was

src/plugin/host-process.cpp

@@ -26,12 +26,6 @@
 namespace bp = boost::process;
 namespace fs = boost::filesystem;
 
-/**
- * Check whether a process with the given PID is still active (and not a
- * zombie).
- */
-bool pid_running(pid_t pid);
-
 /**
  * Simple helper function around `boost::process::child` that launches the host
  * application (`*.exe`) wrapped in winedbg if compiling with
@@ -234,21 +228,3 @@ void GroupHost::terminate() {
     // the sockets will cause the associated plugin to exit.
     sockets.close();
 }
-
-bool pid_running(pid_t pid) {
-    // With regular individually hosted plugins we can simply check whether the
-    // process is still running, however Boost.Process does not allow you to do
-    // the same thing for a process that's not a direct child if this process.
-    // When using plugin groups we'll have to manually check whether the PID
-    // returned by the group host process is still active. We sadly can't use
-    // `kill()` for this as that provides no way to distinguish between active
-    // processes and zombies, and a terminated group host process will always be
-    // left as a zombie process. If the process is active, then
-    // `/proc/<pid>/{cwd,exe,root}` will be valid symlinks.
-    try {
-        fs::canonical("/proc/" + std::to_string(pid) + "/exe");
-        return true;
-    } catch (const fs::filesystem_error&) {
-        return false;
-    }
-}