[Macros] Reap plugin process as soon as it ends

Author: rintaro

include/swift/AST/PluginRegistry.h

@@ -147,7 +147,6 @@ class LoadedExecutablePlugin : public CompilerPlugin {
     const llvm::sys::ProcessInfo process;
     const int input;
     const int output;
-    bool isStale = false;
 
     PluginProcess(llvm::sys::ProcessInfo process, int input, int output)
         : process(process), input(input), output(output) {}
@@ -168,7 +167,7 @@ class LoadedExecutablePlugin : public CompilerPlugin {
 
   /// Mark the current process "stale" (not usable anymore for some reason,
   /// probably crashed).
-  void setStale() { Process->isStale = true; }
+  void setStale() { Process.reset(); }
 
 public:
   LoadedExecutablePlugin(llvm::StringRef ExecutablePath,
@@ -185,7 +184,7 @@ class LoadedExecutablePlugin : public CompilerPlugin {
   }
 
   /// Indicates that the current process is usable.
-  bool isAlive() const { return Process != nullptr && !Process->isStale; }
+  bool isAlive() const { return Process != nullptr; }
 
   // Launch the plugin if it's not already running, or it's stale. Return an
   // error if it's fails to execute it.

lib/AST/PluginRegistry.cpp

@@ -223,16 +223,10 @@ PluginRegistry::loadExecutablePlugin(StringRef path, bool disableSandbox) {
 
 llvm::Error LoadedExecutablePlugin::spawnIfNeeded() {
   if (Process) {
-    // See if the loaded one is still usable.
-    if (!Process->isStale)
-      return llvm::Error::success();
-
     // NOTE: We don't check the mtime here because 'stat(2)' call is too heavy.
     // PluginRegistry::loadExecutablePlugin() checks it and replace this object
     // itself if the plugin is updated.
-
-    // The plugin is stale. Discard the previously opened process.
-    Process.reset();
+    return llvm::Error::success();
   }
 
   // Create command line arguments.