Interface Context

public interface Context
The execution context of a Handler execution.

When Vert.x provides an event to a handler or calls the start or stop methods of a Verticle, the execution is associated with a Context.

Usually a context is an *event-loop context* and is tied to a specific event loop thread. So executions for that context always occur on that exact same event loop thread.

In the case of worker verticles and running inline blocking code a worker context will be associated with the execution which will use a thread from the worker thread pool.

When a handler is set by a thread associated with a specific context, the Vert.x will guarantee that when that handler is executed, that execution will be associated with the same context.

If a handler is set by a thread not associated with a context (i.e. a non Vert.x thread). Then a new context will be created for that handler.

In other words, a context is propagated.

This means that when a verticle is deployed, any handlers it sets will be associated with the same context - the context of the verticle.

This means (in the case of a standard verticle) that the verticle code will always be executed with the exact same thread, so you don't have to worry about multithreaded acccess to the verticle state, and you can code your application as single threaded.

This class also allows arbitrary data to be put(Object, Object) and get(Object) on the context, so it can be shared easily amongst different handlers of, for example, a verticle instance.

This class also provides runOnContext(Handler) which allows an action to be executed asynchronously using the same context.

Author:
Tim Fox

  • Method Details

    • isOnWorkerThread

      static boolean isOnWorkerThread()
      Is the current thread a worker thread?

      NOTE! This is not always the same as calling isWorkerContext(). If you are running blocking code from an event loop context, then this will return true but isWorkerContext() will return false.

      Returns:
      true if current thread is a worker thread, false otherwise

    • isOnEventLoopThread

      static boolean isOnEventLoopThread()
      Is the current thread an event thread?

      NOTE! This is not always the same as calling isEventLoopContext(). If you are running blocking code from an event loop context, then this will return false but isEventLoopContext() will return true.

      Returns:
      true if current thread is an event thread, false otherwise

    • isOnVertxThread

      static boolean isOnVertxThread()
      Is the current thread a Vert.x thread? That's either a worker thread or an event loop thread
      Returns:
      true if current thread is a Vert.x thread, false otherwise

    • runOnContext

      void runOnContext(Handler<Void> action)
      Run the specified action asynchronously on the same context, some time after the current execution has completed.
      Parameters:
      action - the action to run

    • executeBlocking

      <T> Future<T> executeBlocking(Callable<T> blockingCodeHandler, boolean ordered)
      Safely execute some blocking code.

      Executes the blocking code in the handler blockingCodeHandler using a thread from the worker pool.

      The returned future will be completed with the result on the original context (i.e. on the original event loop of the caller) or failed when the handler throws an exception.

      The blocking code should block for a reasonable amount of time (i.e. no more than a few seconds). Long blocking operations or polling operations (i.e a thread that spin in a loop polling events in a blocking fashion) are precluded.

      When the blocking operation lasts more than the 10 seconds, a message will be printed on the console by the blocked thread checker.

      Long blocking operations should use a dedicated thread managed by the application, which can interact with verticles using the event-bus or runOnContext(Handler)

      Type Parameters:
      T - the type of the result
      Parameters:
      blockingCodeHandler - handler representing the blocking code to run
      ordered - if true then if executeBlocking is called several times on the same context, the executions for that context will be executed serially, not in parallel. if false then they will be no ordering guarantees
      Returns:
      a future completed when the blocking code is complete

    • executeBlocking

      default <T> Future<T> executeBlocking(Callable<T> blockingCodeHandler)
      Invoke executeBlocking(Callable, boolean) with order = true.
      Type Parameters:
      T - the type of the result
      Parameters:
      blockingCodeHandler - handler representing the blocking code to run
      Returns:
      a future completed when the blocking code is complete

    • deploymentID

      String deploymentID()
      If the context is associated with a Verticle deployment, this returns the deployment ID of that deployment.
      Returns:
      the deployment ID of the deployment or null if not a Verticle deployment

    • config

      JsonObject config()
      If the context is associated with a Verticle deployment, this returns the configuration that was specified when the verticle was deployed.
      Returns:
      the configuration of the deployment or null if not a Verticle deployment

    • processArgs

      @Deprecated default List<String> processArgs()
      Deprecated.
      As of version 5, Vert.x is no longer tightly coupled to the CLI
      Returns:
      an empty list

    • isEventLoopContext

      boolean isEventLoopContext()
      Is the current context an event loop context?

      NOTE! when running blocking code using Vertx.executeBlocking(Callable) from a standard (not worker) verticle, the context will still an event loop context and this isEventLoopContext() will return true.

      Returns:
      true if the current context is an event-loop context, false otherwise

    • isWorkerContext

      boolean isWorkerContext()
      Is the current context a worker context?

      NOTE! when running blocking code using Vertx.executeBlocking(Callable) from a standard (not worker) verticle, the context will still an event loop context and this

      invalid @link 
      {@link this#isWorkerContext()
      } will return false.
      Returns:
      true if the current context is a worker context, false otherwise

    • threadingModel

      ThreadingModel threadingModel()
      Returns:
      the context threading model

    • get

      <T> T get(Object key)
      Get some data from the context.
      Type Parameters:
      T - the type of the data
      Parameters:
      key - the key of the data
      Returns:
      the data

    • put

      void put(Object key, Object value)
      Put some data in the context.

      This can be used to share data between different handlers that share a context

      Parameters:
      key - the key of the data
      value - the data

    • remove

      boolean remove(Object key)
      Remove some data from the context.
      Parameters:
      key - the key to remove
      Returns:
      true if removed successfully, false otherwise

    • owner

      Vertx owner()
      Returns:
      The Vertx instance that created the context

    • getInstanceCount

      int getInstanceCount()
      Returns:
      the number of instances of the verticle that were deployed in the deployment (if any) related to this context

    • exceptionHandler

      Context exceptionHandler(Handler<Throwable> handler)
      Set an exception handler called when the context runs an action throwing an uncaught throwable.

      When this handler is called, Vertx.currentContext() will return this context.

      Parameters:
      handler - the exception handler
      Returns:
      a reference to this, so the API can be used fluently

    • exceptionHandler

      Handler<Throwable> exceptionHandler()
      Returns:
      the current exception handler of this context

    • getLocal

      default <T> T getLocal(ContextLocal<T> key)
      Get local data associated with key using the concurrent access mode.
      Type Parameters:
      T - the type of the data
      Parameters:
      key - the key of the data
      Returns:
      the local data

    • getLocal

      default <T> T getLocal(ContextLocal<T> key, Supplier<? extends T> initialValueSupplier)

      Get local data associated with key using the concurrent access mode.

      When it does not exist the initialValueSupplier is called to obtain the initial value.

      The initialValueSupplier might be called multiple times when multiple threads call this method concurrently.

      Type Parameters:
      T - the type of the data
      Parameters:
      key - the key of the data
      initialValueSupplier - the supplier of the initial value optionally called
      Returns:
      the local data

    • putLocal

      default <T> void putLocal(ContextLocal<T> key, T value)

      Associate local data with key using the concurrent access mode.

      Parameters:
      key - the key of the data
      value - the data

    • removeLocal

      default <T> void removeLocal(ContextLocal<T> key)

      Remove local data associated with key using the concurrent access mode.

      Parameters:
      key - the key to be removed

    • getLocal

      <T> T getLocal(ContextLocal<T> key, AccessMode accessMode)

      Get local data associated with key using the specified access mode.

      Type Parameters:
      T - the type of the data
      Parameters:
      key - the key of the data
      accessMode - the access mode
      Returns:
      the local data

    • getLocal

      <T> T getLocal(ContextLocal<T> key, AccessMode accessMode, Supplier<? extends T> initialValueSupplier)

      Get local data associated with key using the specified access mode.

      When it does not exist the initialValueSupplier is called to obtain the initial value.

      The initialValueSupplier might be called multiple times when multiple threads call this method concurrently.

      Type Parameters:
      T - the type of the data
      Parameters:
      key - the key of the data
      initialValueSupplier - the supplier of the initial value optionally called
      Returns:
      the local data

    • putLocal

      <T> void putLocal(ContextLocal<T> key, AccessMode accessMode, T value)

      Associate local data with key using the specified access mode.

      Parameters:
      key - the key of the data
      accessMode - the access mode
      value - the data

    • removeLocal

      default <T> void removeLocal(ContextLocal<T> key, AccessMode accessMode)

      Remove local data associated with key using the specified access mode.

      Parameters:
      key - the key to be removed
      accessMode - the access mode