Fix shutdown in --console mode (#14621)

CHANGELOG

@@ -1,6 +1,13 @@
 devel
 -----
 
+* Send a keystroke to arangod's stdin when a shutdown command is received via
+  the REST API `/_admin/shutdown` and the server is started with the
+  `--console` argument. The keystroke will exit the blocking read loop that
+  is waiting on console input and that otherwise blocks the shutdown.
+  The implementation is based on ioctl and is thus only present on Linux and
+  MacOS.
+
 * Some AQL queries erroneously reported the "access after data-modification" 
   error for queries in which there was a read attempt from a collection
   _before_ a data-modification operation. Such access is legal and should not
@@ -21,7 +28,7 @@ devel
   "DATASOURCE_NOT_FOUND". This is now fixed to "BAD_PARAMETER"
   to emphasize that the collection is fine but the input is invalid.
 
-* Fixed: _api/transaction/begin called on edge collections of disjoint
+* Fixed: /_api/transaction/begin called on edge collections of disjoint
   SmartGraphs falsely returned CollectionNotFound errors.
 
 * Bugfix: In more complex queries there was a code-path where a (Disjoint-) 

arangod/RestServer/ConsoleFeature.cpp

@@ -26,6 +26,7 @@
 #include "ConsoleFeature.h"
 
 #include "ApplicationFeatures/ApplicationServer.h"
+#include "Basics/debugging.h"
 #include "Basics/messages.h"
 #include "FeaturePhases/AgencyFeaturePhase.h"
 #include "Logger/LogMacros.h"
@@ -39,15 +40,19 @@
 
 #include <iostream>
 
+#ifndef _WIN32
+#include <sys/ioctl.h>
+#include <unistd.h>
+#endif
+
 using namespace arangodb::application_features;
 using namespace arangodb::options;
 
 namespace arangodb {
 
 ConsoleFeature::ConsoleFeature(application_features::ApplicationServer& server)
     : ApplicationFeature(server, "Console"),
-      _operationMode(OperationMode::MODE_SERVER),
-      _consoleThread(nullptr) {
+      _operationMode(OperationMode::MODE_SERVER) {
   startsAfter<AgencyFeaturePhase>();
 }
 
@@ -65,10 +70,29 @@ void ConsoleFeature::start() {
   auto& sysDbFeature = server().getFeature<arangodb::SystemDatabaseFeature>();
   auto database = sysDbFeature.use();
 
-  _consoleThread.reset(new ConsoleThread(server(), database.get()));
+  _consoleThread = std::make_unique<ConsoleThread>(server(), database.get());
   _consoleThread->start();
 }
 
+void ConsoleFeature::beginShutdown() {
+  if (_operationMode != OperationMode::MODE_CONSOLE) {
+    return;
+  }
+
+  TRI_ASSERT(_consoleThread != nullptr);
+
+  _consoleThread->userAbort();
+
+#ifndef _WIN32
+  if (isatty(STDIN_FILENO)) {
+    char c = '\n';
+    // send ourselves a character, so that we can get out of the blocking
+    // linenoise function that reads a character from the terminal
+    [[maybe_unused]] int res = ioctl(STDIN_FILENO, TIOCSTI, &c);
+  }
+#endif
+}
+
 void ConsoleFeature::unprepare() {
   if (_operationMode != OperationMode::MODE_CONSOLE) {
     return;

arangod/RestServer/ConsoleFeature.h

@@ -27,13 +27,16 @@
 #include "GeneralServer/OperationMode.h"
 #include "RestServer/ConsoleThread.h"
 
+#include <memory>
+
 namespace arangodb {
 
 class ConsoleFeature final : public application_features::ApplicationFeature {
  public:
   explicit ConsoleFeature(application_features::ApplicationServer& server);
 
   void start() override final;
+  void beginShutdown() override final;
   void unprepare() override final;
 
  private: