Do not schedule task if preExecute and postExecute are not overrided.

HMCLCore/src/main/java/org/jackhuang/hmcl/download/game/LibraryDownloadTask.java

@@ -104,6 +104,11 @@ public class LibraryDownloadTask extends Task {
         }
     }
 
+    @Override
+    public boolean doPreExecute() {
+        return true;
+    }
+
     @Override
     public void preExecute() throws Exception {
         Optional<Path> libPath = cacheRepository.getLibrary(originalLibrary);
@@ -135,6 +140,11 @@ public class LibraryDownloadTask extends Task {
         }
     }
 
+    @Override
+    public boolean doPostExecute() {
+        return true;
+    }
+
     @Override
     public void postExecute() throws Exception {
         if (!cached)

HMCLCore/src/main/java/org/jackhuang/hmcl/mod/ModpackUpdateTask.java

@@ -64,6 +64,11 @@ public class ModpackUpdateTask extends Task {
         FileUtils.copyDirectory(repository.getVersionRoot(id).toPath(), backupFolder);
     }
 
+    @Override
+    public boolean doPostExecute() {
+        return true;
+    }
+
     @Override
     public void postExecute() throws Exception {
         if (isDependenciesSucceeded()) {

HMCLCore/src/main/java/org/jackhuang/hmcl/mod/MultiMCModpackInstallTask.java

@@ -96,6 +96,11 @@ public final class MultiMCModpackInstallTask extends Task {
         return dependencies;
     }
 
+    @Override
+    public boolean doPreExecute() {
+        return true;
+    }
+
     @Override
     public void preExecute() throws Exception {
         File run = repository.getRunDirectory(name);

HMCLCore/src/main/java/org/jackhuang/hmcl/task/Task.java

@@ -145,6 +145,10 @@ public abstract class Task {
         this.variables = variables;
     }
 
+    public boolean doPreExecute() {
+        return false;
+    }
+
     /**
      * @throws InterruptedException if current thread is interrupted
      * @see Thread#isInterrupted
@@ -157,6 +161,10 @@ public abstract class Task {
      */
     public abstract void execute() throws Exception;
 
+    public boolean doPostExecute() {
+        return false;
+    }
+
     /**
      * @throws InterruptedException if current thread is interrupted
      * @see Thread#isInterrupted

HMCLCore/src/main/java/org/jackhuang/hmcl/task/TaskExecutor.java

@@ -149,6 +149,7 @@ public final class TaskExecutor {
         try {
             task.setVariables(variables);
 
+            if (task.doPreExecute()) {
                 try {
                     task.getScheduler().schedule(task::preExecute).get();
                 } catch (ExecutionException e) {
@@ -157,6 +158,7 @@ public final class TaskExecutor {
                     else
                         throw e;
                 }
+            }
 
             boolean doDependentsSucceeded = executeTasks(task.getDependents());
             if (!doDependentsSucceeded && task.isRelyingOnDependents() || canceled)
@@ -194,6 +196,7 @@ public final class TaskExecutor {
             if (doDependenciesSucceeded)
                 task.setDependenciesSucceeded();
 
+            if (task.doPostExecute()) {
                 try {
                     task.getScheduler().schedule(task::postExecute).get();
                 } catch (ExecutionException e) {
@@ -202,6 +205,7 @@ public final class TaskExecutor {
                     else
                         throw e;
                 }
+            }
 
             flag = true;
             if (task.getSignificance().shouldLog()) {