Implement the new internal flow engine for Maestro. (#79)

* Implement the new internal flow engine for Maestro.
It uses Java virtual thread feature to greatly simplify the concurrency handling.
It is a highly optimized flow engine to power Maestro engine.

* minor improvements

* fix the incorrect flow deletion during shutdown

* Add task retry during resuming

* fix a few bugs and add some extra java docs

* Improve wakeup and timeout and add an active flag

build.gradle

@@ -119,3 +119,7 @@ configure([project(':maestro-common'), project(':maestro-engine')]) {
         pmdTestFixtures.enabled = true
     }
 }
+
+configure([project(':maestro-flow'), project(':maestro-database')]) {
+    apply plugin: 'java-library'
+}

dependencies.gradle

@@ -6,6 +6,7 @@ ext {
     conductorDep = 'com.netflix.conductor:conductor-core:2.31.5'
     hikaricpDep = 'com.zaxxer:HikariCP:4.+'
     flywayDep = 'org.flywaydb:flyway-core:7.6.+'
+    jacksonAnnotationsDep = 'com.fasterxml.jackson.core:jackson-annotations:2.+'
     jacksonDatabindDep = 'com.fasterxml.jackson.core:jackson-databind:2.+'
     jacksonYamlDep = 'com.fasterxml.jackson.dataformat:jackson-dataformat-yaml:2.+'
     javaxInjectDep = 'javax.inject:javax.inject:1'

maestro-common/src/main/java/com/netflix/maestro/exceptions/MaestroDatabaseError.java

@@ -0,0 +1,21 @@
+package com.netflix.maestro.exceptions;
+
+import com.netflix.maestro.models.error.Details;
+import lombok.Getter;
+
+@Getter
+public class MaestroDatabaseError extends MaestroRuntimeException {
+  private static final long serialVersionUID = 7334668492533395123L;
+
+  private final Details details;
+
+  /**
+   * Constructor with error message and details.
+   *
+   * @param cause cause exception
+   */
+  public MaestroDatabaseError(Throwable cause, String msg) {
+    super(Code.INTERNAL_ERROR, msg, cause);
+    this.details = Details.create(cause, false, msg);
+  }
+}

maestro-engine/src/main/java/com/netflix/maestro/engine/metrics/MaestroMetrics.java → maestro-common/src/main/java/com/netflix/maestro/metrics/MaestroMetrics.java

@@ -10,7 +10,7 @@
  * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
  * specific language governing permissions and limitations under the License.
  */
-package com.netflix.maestro.engine.metrics;
+package com.netflix.maestro.metrics;
 
 /** Maestro metrics interface to record metrics. */
 public interface MaestroMetrics {

maestro-database/README.md

@@ -0,0 +1,4 @@
+Maestro Database
+===================================
+This module includes general classes to implement a maestro persistence layer over JDBC for a specific database system.
+It also includes the utility interfaces needed by maestro components.

maestro-database/build.gradle

@@ -0,0 +1,12 @@
+dependencies {
+    implementation project(':maestro-common')
+    implementation jacksonDatabindDep
+    api hikaricpDep
+    api flywayDep
+
+    testImplementation flywayDep
+    testImplementation testcontainerDep
+    testImplementation postgresqlDep
+    testImplementation hikaricpDep
+    testRuntimeOnly slf4jLog4jDep
+}

maestro-database/gradle.lockfile

@@ -0,0 +1,12 @@
+# This is a Gradle generated file for dependency locking.
+# Manual edits can break the build and are not advised.
+# This file is expected to be part of source control.
+com.fasterxml.jackson.core:jackson-annotations:2.15.4=compileClasspath
+com.fasterxml.jackson.core:jackson-core:2.15.4=compileClasspath
+com.fasterxml.jackson.core:jackson-databind:2.15.4=compileClasspath
+com.fasterxml.jackson:jackson-bom:2.15.4=compileClasspath
+com.zaxxer:HikariCP:4.0.3=compileClasspath
+org.flywaydb:flyway-core:7.6.0=compileClasspath
+org.projectlombok:lombok:1.18.36=annotationProcessor,compileClasspath
+org.slf4j:slf4j-api:1.7.30=compileClasspath
+empty=