Allow disabling process killing on interruption (#3293)

* Allow disabling process killing on interuption

Plugins may want to do custom action when the execution of a remote process is interrupted. Currently it is not possible, because
the process started on a slave is killed on interruption.
My actual use case: https://groups.google.com/forum/#!msg/jenkinsci-dev/s6IkynOzdqE/2eFNKN9lAAAJ

My solution is to have a flag called killWhenInterrupted, set by default to true, which prevents process killing on the slave when unset.

* Invert killWhenInterrupted flag

* Add javadoc

core/src/main/java/hudson/Launcher.java

@@ -181,6 +181,12 @@ public abstract class Launcher {
          */
         protected boolean reverseStdin, reverseStdout, reverseStderr;
 
+        /**
+         * True to prevent killing the launched process when it is interrupted
+         * @since TODO
+         */
+        protected boolean dontKillWhenInterrupted;
+
         /**
          * Passes a white-space separated single-string command (like "cat abc def") and parse them
          * as a command argument. This method also handles quotes.
@@ -441,6 +447,22 @@ public abstract class Launcher {
             return this;
         }
 
+        /**
+         * Indicates that the launched process should not be killed when interrupted.
+         * It allows detecting the interruption on caller's side and do custom (cleanup) action while 
+         * the launched process is still running. 
+         * 
+         * <p>
+         * Note that the process can (and should) be killed
+         * via {@link Proc#kill()} when custom action is done.
+         * 
+         * @return {@code this}
+         * @since TODO
+         */
+        public ProcStarter dontKillWhenInterrupted() {
+            this.dontKillWhenInterrupted = true;
+            return this;
+        }
 
         /**
          * Starts the new process as configured.
@@ -926,7 +948,7 @@ public abstract class Launcher {
                     ps.reverseStdin ?LocalProc.SELFPUMP_INPUT:ps.stdin,
                     ps.reverseStdout?LocalProc.SELFPUMP_OUTPUT:ps.stdout,
                     ps.reverseStderr?LocalProc.SELFPUMP_OUTPUT:ps.stderr,
-                    toFile(ps.pwd));
+                    toFile(ps.pwd), ps.dontKillWhenInterrupted);
         }
 
         private File toFile(FilePath f) {
@@ -1049,7 +1071,8 @@ public abstract class Launcher {
             final String workDir = psPwd==null ? null : psPwd.getRemote();
 
             try {
-                return new ProcImpl(getChannel().call(new RemoteLaunchCallable(ps.commands, ps.masks, ps.envs, in, ps.reverseStdin, out, ps.reverseStdout, err, ps.reverseStderr, ps.quiet, workDir, listener)));
+                return new ProcImpl(getChannel().call(new RemoteLaunchCallable(ps.commands, ps.masks, ps.envs, in, ps.reverseStdin,
+                        out, ps.reverseStdout, err, ps.reverseStderr, ps.quiet, workDir, listener, ps.dontKillWhenInterrupted)));
             } catch (InterruptedException e) {
                 throw (IOException)new InterruptedIOException().initCause(e);
             }
@@ -1267,12 +1290,14 @@ public abstract class Launcher {
         private final @Nonnull TaskListener listener;
         private final boolean reverseStdin, reverseStdout, reverseStderr;
         private final boolean quiet;
-
-        RemoteLaunchCallable(@Nonnull List<String> cmd, @CheckForNull boolean[] masks, @CheckForNull String[] env, 
-                @CheckForNull InputStream in, boolean reverseStdin, 
-                @CheckForNull OutputStream out, boolean reverseStdout, 
-                @CheckForNull OutputStream err, boolean reverseStderr, 
-                boolean quiet, @CheckForNull String workDir, @Nonnull TaskListener listener) {
+        private final boolean dontKillWhenInterrupted;
+
+        RemoteLaunchCallable(@Nonnull List<String> cmd, @CheckForNull boolean[] masks, @CheckForNull String[] env,
+                @CheckForNull InputStream in, boolean reverseStdin,
+                @CheckForNull OutputStream out, boolean reverseStdout,
+                @CheckForNull OutputStream err, boolean reverseStderr,
+                boolean quiet, @CheckForNull String workDir,
+                @Nonnull TaskListener listener, boolean dontKillWhenInterrupted) {
             this.cmd = new ArrayList<>(cmd);
             this.masks = masks;
             this.env = env;
@@ -1285,6 +1310,7 @@ public abstract class Launcher {
             this.reverseStdout = reverseStdout;
             this.reverseStderr = reverseStderr;
             this.quiet = quiet;
+            this.dontKillWhenInterrupted = dontKillWhenInterrupted;
         }
 
         public RemoteProcess call() throws IOException {
@@ -1295,6 +1321,7 @@ public abstract class Launcher {
             if (reverseStdin)   ps.writeStdin();
             if (reverseStdout)  ps.readStdout();
             if (reverseStderr)  ps.readStderr();
+            if (dontKillWhenInterrupted) ps.dontKillWhenInterrupted();
 
             final Proc p = ps.start();
 

core/src/main/java/hudson/Proc.java

@@ -64,6 +64,12 @@ import org.kohsuke.accmod.restrictions.NoExternalUse;
 public abstract class Proc {
     protected Proc() {}
 
+    /**
+     * Indicates that the process should not be killed on interruption.
+     * @since TODO
+     */
+    protected boolean dontKillWhenInterrupted;
+
     /**
      * Checks if the process is still alive.
      */
@@ -207,17 +213,17 @@ public abstract class Proc {
         }
 
         public LocalProc(String[] cmd,String[] env,InputStream in,OutputStream out, File workDir) throws IOException {
-            this(cmd,env,in,out,null,workDir);
+            this(cmd,env,in,out,null,workDir, true);
         }
 
         /**
          * @param err
          *      null to redirect stderr to stdout.
          */
-        public LocalProc(String[] cmd,String[] env,InputStream in,OutputStream out,OutputStream err,File workDir) throws IOException {
+        public LocalProc(String[] cmd,String[] env,InputStream in,OutputStream out,OutputStream err,File workDir, boolean dontKillWhenInterrupted) throws IOException {
             this( calcName(cmd),
                   stderr(environment(new ProcessBuilder(cmd),env).directory(workDir), err==null || err== SELFPUMP_OUTPUT),
-                  in, out, err );
+                  in, out, err, dontKillWhenInterrupted);
         }
 
         private static ProcessBuilder stderr(ProcessBuilder pb, boolean redirectError) {
@@ -237,10 +243,11 @@ public abstract class Proc {
             return pb;
         }
 
-        private LocalProc( String name, ProcessBuilder procBuilder, InputStream in, OutputStream out, OutputStream err ) throws IOException {
+        private LocalProc( String name, ProcessBuilder procBuilder, InputStream in, OutputStream out, OutputStream err, boolean dontKillWhenInterrupted ) throws IOException {
             Logger.getLogger(Proc.class.getName()).log(Level.FINE, "Running: {0}", name);
             this.name = name;
             this.out = out;
+            this.dontKillWhenInterrupted = dontKillWhenInterrupted;
             this.cookie = EnvVars.createCookie();
             procBuilder.environment().putAll(cookie);
             if (procBuilder.directory() != null && !procBuilder.directory().exists()) {
@@ -354,7 +361,9 @@ public abstract class Proc {
                 return r;
             } catch (InterruptedException e) {
                 // aborting. kill the process
-                destroy();
+                if (!dontKillWhenInterrupted) {
+                    destroy();
+                }
                 throw e;
             } finally {
                 t.setName(oldName);
@@ -462,7 +471,9 @@ public abstract class Proc {
                 return process.get();
             } catch (InterruptedException e) {
                 LOGGER.log(Level.FINE, String.format("Join operation has been interrupted for the process %s. Killing the process", this), e);
-                kill();
+                if (!dontKillWhenInterrupted) {
+                    kill();
+                }
                 throw e;
             } catch (ExecutionException e) {
                 if(e.getCause() instanceof IOException)