[BuildSystem] Add execution queue delegate handler for process errors.

Author: ddunbar

include/llbuild/BuildSystem/BuildExecutionQueue.h

@@ -178,6 +178,15 @@ class BuildExecutionQueueDelegate {
   /// provided to the \see commandProcessFinished() call.
   virtual void commandProcessStarted(Command*, ProcessHandle handle) = 0;
 
+  /// Called to report an error in the management of a command process.
+  ///
+  /// \param handle - The process handle.
+  /// \param message - The error message.
+  //
+  // FIXME: Need to move to more structured error handling.
+  virtual void commandProcessHadError(Command*, ProcessHandle handle,
+                                      const Twine& message) = 0;
+
   /// Called to report a command processes' (merged) standard output and error.
   ///
   /// \param handle - The process handle.
@@ -190,7 +199,8 @@ class BuildExecutionQueueDelegate {
   /// \param handle - The handle used to identify the process. This handle will
   /// become invalid as soon as the client returns from this API call.
   ///
-  /// \param exitStatus - The exit status of the process.
+  /// \param exitStatus - The exit status of the process, or -1 if an error was
+  /// encountered.
   //
   // FIXME: Need to include additional information on the status here, e.g., the
   // signal status, and the process output (if buffering).

include/llbuild/BuildSystem/BuildSystemFrontend.h

@@ -166,6 +166,15 @@ class BuildSystemFrontendDelegate : public BuildSystemDelegate {
   /// provided to the \see commandProcessFinished() call.
   virtual void commandProcessStarted(Command*, ProcessHandle handle);
 
+  /// Called to report an error in the management of a command process.
+  ///
+  /// \param handle - The process handle.
+  /// \param message - The error message.
+  //
+  // FIXME: Need to move to more structured error handling.
+  virtual void commandProcessHadError(Command*, ProcessHandle handle,
+                                       const Twine& message);
+
   /// Called to report a command processes' (merged) standard output and error.
   ///
   /// \param handle - The process handle.

lib/BuildSystem/BuildSystemFrontend.cpp

@@ -155,6 +155,14 @@ class BuildSystemFrontendExecutionQueueDelegate
           command, BuildSystemFrontendDelegate::ProcessHandle { handle.id });
   }
 
+  virtual void commandProcessHadError(Command* command, ProcessHandle handle,
+                                      const Twine& message) override {
+    static_cast<BuildSystemFrontendDelegate*>(&getSystem().getDelegate())->
+      commandProcessHadError(
+          command, BuildSystemFrontendDelegate::ProcessHandle { handle.id },
+          message);
+  }
+  
   virtual void commandProcessHadOutput(Command* command, ProcessHandle handle,
                                        StringRef data) override {
     static_cast<BuildSystemFrontendDelegate*>(&getSystem().getDelegate())->
@@ -352,6 +360,17 @@ void BuildSystemFrontendDelegate::commandProcessStarted(Command* command,
   fflush(stdout);
 }
 
+void BuildSystemFrontendDelegate::
+commandProcessHadError(Command* command, ProcessHandle handle,
+                       const Twine& message) {
+  SmallString<256> buffer;
+  auto str = message.toStringRef(buffer);
+  
+  // FIXME: Design the logging and status output APIs.
+  fwrite(str.data(), str.size(), 1, stderr);
+  fflush(stderr);
+}
+  
 void BuildSystemFrontendDelegate::
 commandProcessHadOutput(Command* command, ProcessHandle handle,
                         StringRef data) {

lib/BuildSystem/LaneBasedExecutionQueue.cpp

@@ -191,9 +191,9 @@ class LaneBasedExecutionQueue : public BuildExecutionQueue {
     int outputPipe[2]{ -1, -1 };
     if (shouldCaptureOutput) {
       if (::pipe(outputPipe) < 0) {
-        // FIXME: Error handling.
-        fprintf(stderr, "error: unable to spawn process (%s)\n",
-                strerror(errno));
+        getDelegate().commandProcessHadError(
+            context.job.getForCommand(), handle,
+            Twine("unable to open output pipe (") + strerror(errno) + ")");
         getDelegate().commandProcessFinished(context.job.getForCommand(),
                                              handle, -1);
         return false;
@@ -240,9 +240,9 @@ class LaneBasedExecutionQueue : public BuildExecutionQueue {
     if (posix_spawn(&pid, args[0], /*file_actions=*/&fileActions,
                     /*attrp=*/&attributes, const_cast<char**>(args.data()),
                     ::environ) != 0) {
-      // FIXME: Error handling.
-      fprintf(stderr, "error: unable to spawn process (%s)\n", strerror(errno));
-      // FIXME: Communicate error status appropriately.
+      getDelegate().commandProcessHadError(
+          context.job.getForCommand(), handle,
+          Twine("unable to spawn process (") + strerror(errno) + ")");
       getDelegate().commandProcessFinished(context.job.getForCommand(), handle,
                                            -1);
       return false;
@@ -262,9 +262,9 @@ class LaneBasedExecutionQueue : public BuildExecutionQueue {
         char buf[4096];
         ssize_t numBytes = read(outputPipe[0], buf, sizeof(buf));
         if (numBytes < 0) {
-          // FIXME: Error handling.
-          fprintf(stderr, "error: unable to read from output pipe (%s)\n",
-                  strerror(errno));
+          getDelegate().commandProcessHadError(
+              context.job.getForCommand(), handle,
+              Twine("unable to read process output (") + strerror(errno) + ")");
           break;
         }
 
@@ -283,10 +283,9 @@ class LaneBasedExecutionQueue : public BuildExecutionQueue {
     while (result == -1 && errno == EINTR)
       result = waitpid(pid, &status, 0);
     if (result == -1) {
-      // FIXME: Error handling.
-      fprintf(stderr, "error: unable to wait for process (%s)\n",
-              strerror(errno));
-      // FIXME: Communicate error status appropriately.
+      getDelegate().commandProcessHadError(
+          context.job.getForCommand(), handle,
+          Twine("unable to wait for process (") + strerror(errno) + ")");
       getDelegate().commandProcessFinished(context.job.getForCommand(), handle,
                                            -1);
       return false;
@@ -299,6 +298,8 @@ class LaneBasedExecutionQueue : public BuildExecutionQueue {
     }
 
     // Notify of the process completion.
+    //
+    // FIXME: Need to communicate more information on the process exit status.
     getDelegate().commandProcessFinished(context.job.getForCommand(), handle,
                                          status);
     return (status == 0);