Reimplement restarting of scm-manager

SCM-Manager tries now to figure out which is the best strategy for the restart.
It chooses from one of the following strategies:

* PosixRestartStrategy which uses native LibC
* ExitRestartStrategy uses System.exit and relies on external mechanism to start again
* InjectionContextRestartStrategy destroys and re initializes the injection context

scm-webapp/pom.xml

@@ -295,6 +295,20 @@
       <version>2.7.0</version>
     </dependency>
 
+    <!-- unix restart -->
+
+    <dependency>
+      <groupId>org.kohsuke</groupId>
+      <artifactId>akuma</artifactId>
+      <version>1.10</version>
+    </dependency>
+
+    <dependency>
+      <groupId>net.java.dev.jna</groupId>
+      <artifactId>jna</artifactId>
+      <version>5.5.0</version>
+    </dependency>
+
     <!-- test scope -->
 
     <dependency>

scm-webapp/src/main/java/sonia/scm/lifecycle/BootstrapContextFilter.java

@@ -42,6 +42,7 @@ import sonia.scm.event.ScmEventBus;
 import javax.servlet.FilterConfig;
 import javax.servlet.ServletContextEvent;
 import javax.servlet.ServletException;
+import java.util.Optional;
 
 //~--- JDK imports ------------------------------------------------------------
 
@@ -100,8 +101,12 @@ public class BootstrapContextFilter extends GuiceFilter {
     if (filterConfig == null) {
       LOG.error("filter config is null, scm-manager is not initialized");
     } else {
-      RestartStrategy restartStrategy = RestartStrategy.get(webAppClassLoader);
-      restartStrategy.restart(new GuiceInjectionContext());
+      Optional<RestartStrategy> restartStrategy = RestartStrategy.get(webAppClassLoader);
+      if (restartStrategy.isPresent()) {
+        restartStrategy.get().restart(new GuiceInjectionContext());
+      } else {
+        LOG.warn("restarting is not supported by the underlying platform");
+      }
     }
   }
 

scm-webapp/src/main/java/sonia/scm/lifecycle/CLibrary.java

@@ -0,0 +1,22 @@
+package sonia.scm.lifecycle;
+
+/**
+ * Interface for native c library.
+ */
+@SuppressWarnings({
+  "squid:S1214", // usage as constant is common practice for jna
+  "squid:S1191"  // use of sun.* classes is required for jna
+})
+interface CLibrary extends com.sun.jna.Library {
+  CLibrary LIBC =  com.sun.jna.Native.load("c", CLibrary.class);
+
+  int F_GETFD = 1;
+  int F_SETFD = 2;
+  int FD_CLOEXEC = 1;
+
+  int getdtablesize();
+  int fcntl(int fd, int command);
+  int fcntl(int fd, int command, int flags);
+  int execvp(String file, com.sun.jna.StringArray args);
+  String strerror(int errno);
+}

scm-webapp/src/main/java/sonia/scm/lifecycle/ExitRestartStrategy.java

@@ -0,0 +1,52 @@
+package sonia.scm.lifecycle;
+
+import com.google.common.annotations.VisibleForTesting;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.util.function.IntConsumer;
+
+/**
+ * {@link RestartStrategy} which tears down the scm-manager context and
+ * then exists the java process with {@link System#exit(int)}.
+ * <p>
+ * This is useful if an external mechanism is able to restart the process after it has exited.
+ */
+class ExitRestartStrategy implements RestartStrategy {
+
+  private static final Logger LOG = LoggerFactory.getLogger(ExitRestartStrategy.class);
+
+  static final String NAME = "exit";
+
+  static final String PROPERTY_EXIT_CODE = "sonia.scm.restart.exit-code";
+
+  private IntConsumer exiter = System::exit;
+
+  ExitRestartStrategy() {
+  }
+
+  @VisibleForTesting
+  void setExiter(IntConsumer exiter) {
+    this.exiter = exiter;
+  }
+
+  @Override
+  public void restart(InjectionContext context) {
+    int exitCode = determineExitCode();
+
+    LOG.warn("destroy injection context");
+    context.destroy();
+
+    LOG.warn("exit scm-manager with exit code {}", exitCode);
+    exiter.accept(exitCode);
+  }
+
+  private int determineExitCode() {
+    String exitCodeAsString = System.getProperty(PROPERTY_EXIT_CODE, "0");
+    try {
+      return Integer.parseInt(exitCodeAsString);
+    } catch (NumberFormatException ex) {
+      throw new RestartNotSupportedException("invalid exit code " + exitCodeAsString, ex);
+    }
+  }
+}

scm-webapp/src/main/java/sonia/scm/lifecycle/InjectionContextRestartStrategy.java

@@ -10,9 +10,11 @@ import sonia.scm.event.ShutdownEventBusEvent;
 import java.util.concurrent.atomic.AtomicLong;
 
 /**
- * Restart strategy implementation which destroy the injection context and re initialize it.
+ * Restart strategy which tries to free, every resource used by the context, starts gc and re initializes the context.
  */
-public class InjectionContextRestartStrategy implements RestartStrategy {
+class InjectionContextRestartStrategy implements RestartStrategy {
+
+  static final String NAME = "context";
 
   private static final String DISABLE_RESTART_PROPERTY = "sonia.scm.restart.disable";
   private static final String WAIT_PROPERTY = "sonia.scm.restart.wait";

scm-webapp/src/main/java/sonia/scm/lifecycle/PosixRestartStrategy.java

@@ -0,0 +1,52 @@
+package sonia.scm.lifecycle;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+
+import static sonia.scm.lifecycle.CLibrary.*;
+
+/**
+ * Restart strategy which uses execvp from libc. This strategy is only supported on posix base operating systems.
+ */
+class PosixRestartStrategy implements RestartStrategy {
+
+  private static final Logger LOG = LoggerFactory.getLogger(PosixRestartStrategy.class);
+
+  PosixRestartStrategy() {
+  }
+
+  @Override
+  public void restart(InjectionContext context) {
+    LOG.warn("destroy injection context");
+    context.destroy();
+
+    LOG.warn("restart scm-manager jvm process");
+    try {
+      restart();
+    } catch (IOException e) {
+      LOG.error("failed to collect java vm arguments", e);
+      LOG.error("we will now exit the java process");
+      System.exit(1);
+    }
+  }
+
+  @SuppressWarnings("squid:S1191") // use of sun.* classes is required for jna)
+  private static void restart() throws IOException {
+    com.sun.akuma.JavaVMArguments args = com.sun.akuma.JavaVMArguments.current();
+    args.remove("--daemon");
+
+    int sz = LIBC.getdtablesize();
+    for(int i=3; i<sz; i++) {
+      int flags = LIBC.fcntl(i, F_GETFD);
+      if(flags<0) continue;
+      LIBC.fcntl(i, F_SETFD,flags| FD_CLOEXEC);
+    }
+
+    // exec to self
+    String exe = args.get(0);
+    LIBC.execvp(exe, new com.sun.jna.StringArray(args.toArray(new String[0])));
+    throw new IOException("Failed to exec '"+exe+"' "+LIBC.strerror(com.sun.jna.Native.getLastError()));
+  }
+}

scm-webapp/src/main/java/sonia/scm/lifecycle/RestartNotSupportedException.java

@@ -0,0 +1,10 @@
+package sonia.scm.lifecycle;
+
+/**
+ * Exception is thrown if a restart is not supported or a restart strategy is misconfigured.
+ */
+public class RestartNotSupportedException extends RuntimeException {
+  RestartNotSupportedException(String message, Throwable cause) {
+    super(message, cause);
+  }
+}

scm-webapp/src/main/java/sonia/scm/lifecycle/RestartStrategy.java

@@ -1,5 +1,7 @@
 package sonia.scm.lifecycle;
 
+import java.util.Optional;
+
 /**
  * Strategy for restarting SCM-Manager.
  */
@@ -13,6 +15,7 @@ public interface RestartStrategy {
      * Initialize the injection context.
      */
     void initialize();
+
     /**
      * Destroys the injection context.
      */
@@ -21,17 +24,19 @@ public interface RestartStrategy {
 
   /**
    * Restart SCM-Manager.
+   *
    * @param context injection context
    */
   void restart(InjectionContext context);
 
   /**
-   * Returns the configured strategy.
+   * Returns the configured strategy or empty if restart is not supported by the underlying platform.
    *
-   * @return configured strategy
+   * @param webAppClassLoader root webapp classloader
+   * @return configured strategy or empty optional
    */
-  static RestartStrategy get(ClassLoader webAppClassLoader) {
-    return new InjectionContextRestartStrategy(webAppClassLoader);
+  static Optional<RestartStrategy> get(ClassLoader webAppClassLoader) {
+    return Optional.ofNullable(RestartStrategyFactory.create(webAppClassLoader));
   }
 
 }

scm-webapp/src/main/java/sonia/scm/lifecycle/RestartStrategyFactory.java

@@ -0,0 +1,66 @@
+package sonia.scm.lifecycle;
+
+import com.google.common.base.Strings;
+import sonia.scm.PlatformType;
+import sonia.scm.util.SystemUtil;
+
+final class RestartStrategyFactory {
+
+  /**
+   * System property to load a specific restart strategy.
+   */
+  static final String PROPERTY_STRATEGY = "sonia.scm.lifecycle.restart-strategy";
+
+  /**
+   * No restart supported.
+   */
+  static final  String STRATEGY_NONE = "none";
+
+  private RestartStrategyFactory() {
+  }
+
+  /**
+   * Returns the configured strategy or {@code null} if restart is not supported.
+   *
+   * @param webAppClassLoader root webapp classloader
+   * @return configured strategy or {@code null}
+   */
+  static RestartStrategy create(ClassLoader webAppClassLoader) {
+    String property = System.getProperty(PROPERTY_STRATEGY);
+    if (Strings.isNullOrEmpty(property)) {
+      return forPlatform();
+    }
+    return fromProperty(webAppClassLoader, property);
+  }
+
+  private static RestartStrategy fromProperty(ClassLoader webAppClassLoader, String property) {
+    if (STRATEGY_NONE.equalsIgnoreCase(property)) {
+      return null;
+    } else if (ExitRestartStrategy.NAME.equalsIgnoreCase(property)) {
+      return new ExitRestartStrategy();
+    } else if (InjectionContextRestartStrategy.NAME.equalsIgnoreCase(property)) {
+      return new InjectionContextRestartStrategy(webAppClassLoader);
+    } else {
+      return fromClassName(property);
+    }
+  }
+
+  private static RestartStrategy fromClassName(String property) {
+    try {
+      Class<? extends RestartStrategy> rsClass = Class.forName(property).asSubclass(RestartStrategy.class);
+      return rsClass.getConstructor().newInstance();
+    } catch (Exception e) {
+      throw new RestartNotSupportedException("failed to create restart strategy from property", e);
+    }
+  }
+
+  private static RestartStrategy forPlatform() {
+    // we do not use SystemUtil here, to allow testing
+    String osName = System.getProperty(SystemUtil.PROPERTY_OSNAME);
+    PlatformType platform = PlatformType.createPlatformType(osName);
+    if (platform.isPosix()) {
+      return new PosixRestartStrategy();
+    }
+    return null;
+  }
+}

scm-webapp/src/test/java/sonia/scm/lifecycle/ExitRestartStrategyTest.java

@@ -0,0 +1,75 @@
+package sonia.scm.lifecycle;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.function.IntConsumer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.verify;
+
+@ExtendWith(MockitoExtension.class)
+class ExitRestartStrategyTest {
+
+  @Mock
+  private RestartStrategy.InjectionContext context;
+
+  private ExitRestartStrategy strategy;
+  private CapturingExiter exiter;
+
+  @BeforeEach
+  void setUpStrategy() {
+    strategy = new ExitRestartStrategy();
+    exiter = new CapturingExiter();
+    strategy.setExiter(exiter);
+  }
+
+  @Test
+  void shouldTearDownContextAndThenExit() {
+    strategy.restart(context);
+
+    verify(context).destroy();
+    assertThat(exiter.getExitCode()).isEqualTo(0);
+  }
+
+  @Test
+  void shouldUseExitCodeFromSystemProperty() {
+    System.setProperty(ExitRestartStrategy.PROPERTY_EXIT_CODE, "42");
+    try {
+      strategy.restart(context);
+
+      verify(context).destroy();
+      assertThat(exiter.getExitCode()).isEqualTo(42);
+    } finally {
+      System.clearProperty(ExitRestartStrategy.PROPERTY_EXIT_CODE);
+    }
+  }
+
+  @Test
+  void shouldThrowExceptionForNonNumericExitCode() {
+    System.setProperty(ExitRestartStrategy.PROPERTY_EXIT_CODE, "xyz");
+    try {
+      assertThrows(RestartNotSupportedException.class, () -> strategy.restart(context));
+    } finally {
+      System.clearProperty(ExitRestartStrategy.PROPERTY_EXIT_CODE);
+    }
+  }
+
+  private static class CapturingExiter implements IntConsumer {
+
+    private int exitCode = -1;
+
+    public int getExitCode() {
+      return exitCode;
+    }
+
+    @Override
+    public void accept(int exitCode) {
+      this.exitCode = exitCode;
+    }
+  }
+}

scm-webapp/src/test/java/sonia/scm/lifecycle/RestartStrategyTest.java

@@ -0,0 +1,101 @@
+package sonia.scm.lifecycle;
+
+import com.google.common.base.Strings;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+import sonia.scm.util.SystemUtil;
+
+import java.util.Optional;
+import java.util.function.Consumer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+class RestartStrategyTest {
+  private final ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+
+  @Test
+  void shouldReturnRestartStrategyFromSystemProperty() {
+    withStrategy(TestingRestartStrategy.class.getName(), (rs) -> {
+      assertThat(rs).containsInstanceOf(TestingRestartStrategy.class);
+    });
+  }
+
+  @Test
+  void shouldThrowExceptionForNonStrategyClass() {
+    withStrategy(RestartStrategyTest.class.getName(), () -> {
+      assertThrows(RestartNotSupportedException.class, () -> RestartStrategy.get(classLoader));
+    });
+  }
+
+  @Test
+  void shouldReturnEmpty() {
+    withStrategy(RestartStrategyFactory.STRATEGY_NONE, (rs) -> {
+      assertThat(rs).isEmpty();
+    });
+  }
+
+  @Test
+  void shouldReturnEmptyForUnknownOs() {
+    withSystemProperty(SystemUtil.PROPERTY_OSNAME, "hitchhiker-os", () -> {
+      Optional<RestartStrategy> restartStrategy = RestartStrategy.get(classLoader);
+      assertThat(restartStrategy).isEmpty();
+    });
+  }
+
+  @Test
+  void shouldReturnExitRestartStrategy() {
+    withStrategy(ExitRestartStrategy.NAME, (rs) -> {
+      assertThat(rs).containsInstanceOf(ExitRestartStrategy.class);
+    });
+  }
+
+  @Test
+  void shouldReturnInjectionContextRestartStrategy() {
+    withStrategy(InjectionContextRestartStrategy.NAME, (rs) -> {
+      assertThat(rs).containsInstanceOf(InjectionContextRestartStrategy.class);
+    });
+  }
+
+  @ParameterizedTest
+  @ValueSource(strings = { "linux", "darwin", "solaris", "freebsd", "openbsd" })
+  void shouldReturnPosixRestartStrategyForPosixBased(String os) {
+    withSystemProperty(SystemUtil.PROPERTY_OSNAME, os, () -> {
+      Optional<RestartStrategy> restartStrategy = RestartStrategy.get(classLoader);
+      assertThat(restartStrategy).containsInstanceOf(PosixRestartStrategy.class);
+    });
+  }
+
+  private void withStrategy(String strategy, Consumer<Optional<RestartStrategy>> consumer) {
+      withStrategy(strategy, () -> {
+        consumer.accept(RestartStrategy.get(classLoader));
+      });
+  }
+
+  private void withStrategy(String strategy, Runnable runnable) {
+    withSystemProperty(RestartStrategyFactory.PROPERTY_STRATEGY, strategy, runnable);
+  }
+
+  private void withSystemProperty(String key, String value, Runnable runnable) {
+    String oldValue = System.getProperty(key);
+    System.setProperty(key, value);
+    try {
+      runnable.run();
+    } finally {
+      if (Strings.isNullOrEmpty(oldValue)) {
+        System.clearProperty(key);
+      } else {
+        System.setProperty(key, oldValue);
+      }
+    }
+  }
+
+  public static class TestingRestartStrategy implements RestartStrategy {
+    @Override
+    public void restart(InjectionContext context) {
+
+    }
+  }
+
+}