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Activiti User Guide. The following sections cover advanced use cases of using Activiti, that go beyond typical execution of BPMN 2. As such, a certain proficiency and experience with Activiti is advisable to understand the material here. Async and job executor. Starting from version 5. Activiti provides the Async executor in addition to the existing job executor. Both executors deal with timers and asynchronous jobs in the Activiti Engine, so only one executor can be enabled. Note that by default Activiti uses the existing job executor because we don’t want to enable the Async executor without making an explicit configuration for it. Async executor design. The Async executor contains a thread pool to execute timer and asynchronous jobs. When enabled, the Engine will call the Async executor with a persisted asynchronous job entity and the thread pool will asynchronously execute the job. The Async executor will execute the asynchronous job directly without first polling the database. The job will then be locked and executed. Job executor design. Q: How do I obtain, configure, and build ACE and TAO on Windows with Visual C++? A: This FAQ provides basic instructions for installing and building ACE+TAO for Windows with Visual C++. ACE+TAO can also be used on other major. Linux Processes and Signals, Each process is allocated a unique number, process identifier (PID). It's an integer between 2 and 32,768. When a process is started, the numbers restart from 2, and the number 1 is typically. The job executor also contains a thread pool to execute timer and asynchronous jobs. When activated, the Job executor will poll the database for asynchronous jobs and timer jobs due. On the other side, the Async executor will execute the asynchronous job directly without first polling the database. 1.1 Where does this specification fit? This specification defines a big part of the Web platform, in lots of detail. Its place in the Web platform specification stack relative to other specifications can be best summed up as. The book 'Java for Kids' was written by Yakov Fain, Java Champion. The goal is to help students learn to program in the most popular language in the world: Java. This book starts from an introduction to Java and then explains. Common WinDbg Commands (Thematically Grouped), by Robert Kuster. 4) Expressions and commands; Cmd Variants / Params Description; Command separator (cm1; cm2.)?? Advantages of the Async executor. Less database queries because asynchronous jobs are executed without polling the database. For non- exclusive jobs there’s no chance to run into Optimistic. Locking. Exceptions anymore. Exclusive jobs are now locked at process instance level instead of the cumbersome logic of queuing exclusive jobs in the Job Executor. Async executor configuration. It’s possible to define thread pool sizes and other configurations for the Async executor. Async executor configuration options. Name. Default value. Descriptioncore. Pool. Size. 2The minimal number of threads that are kept alive in the thread pool for job execution. Pool. Size. 10. The maximum number of threads that are kept alive in the thread pool for job execution. Alive. Time. 50. 00. The time (in milliseconds) a thread used for job execution must be kept alive before it is destroyed. Having a non- default setting of 0 takes resources, but in the case of many job executions it avoids creating new threads all the time. Size. 10. 0The size of the queue on which jobs to be executed are placed. Timer. Jobs. Per. Acquisition. 1The number of timer jobs that are fetched from the database in one query. Async. Jobs. Due. Per. Acquisition. The number of asynchronous jobs due that are fetched from the database in one query. Async. Job. Acquire. Wait. Time. In. Millis. The time in milliseconds between asynchronous job due queries being executed. Timer. Job. Acquire. Wait. Time. In. Millis. The time in milliseconds between timer job queries being executed. Lock. Time. In. Millis. The time in milliseconds that a timer job is locked before being retried again. The Activiti Engine considers the timer job to have failed after this period of time and will retry. Job. Lock. Time. In. Millis. 30. 00. 00. The time in milliseconds that an asynchronous job is locked before being retried again. The Activiti Engine considers the asynchronous job to have failed after this period of time and will retry. Hooking into process parsing. A BPMN 2. 0 xml needs to be parsed to the Activiti internal model to be executed on the Activiti engine. This parsing happens during a deployment of the process or when a process is not found in memory, and the xml is fetched from the database. For each of these processes, the Bpmn. Parser class creates a new Bpmn. Parse instance. This instance will be used as container for all things that are done during parsing. The parsing on itself is very simple: for each BPMN 2. Bpmn. Parse. Handler available in the engine. As such, the parser has a map which basically maps a BPMN 2. Bpmn. Parse. Handler. By default, Activiti has Bpmn. Parse. Handler instances to handle all supported elements and also uses it to attach execution listeners to steps of the process for creating the history. It is possible to add custom instances of org. Bpmn. Parse. Handler to the Activiti engine. An often seen use case is for example to add execution listeners to certain steps that fire events to some queue for event processing. The history handling is done in such a way internally in Activiti. To add such custom handlers, the Activiti configuration needs to be tweaked: 1. Likewise, the post. Bpmn. Parse. Handlers are added after those. This can be important if the order of things matter for the logic contained in the custom parse handlers. Bpmn. Parse. Handler is a simple interface: 1. Bpmn. Parse. Handler. You can also extend the Abstract. Bpmn. Parse. Handler class and override the get. Handled. Type() method, which only returns one Class and not a collection. This class contains also some helper methods shared by many of the default parse handlers. In the following example, whenever a process contained in a BPMN 2. Parse method (which is a typecasted method that replaces the regular parse method on the Bpmn. Parse. Handler interface). Test. BPMNParse. Handlerextends. Abstract. Bpmn. Parse. Handler< Process>. This will cause difficult to find bugs. The safe way to implement a custom handler is to implement the Bpmn. Parse. Handler interface or extends the internal abstract class org. Abstract. Bpmn. Parse. Handler. It is possible (but less common) to replace the default Bpmn. Parse. Handler instances that are responsible for the parsing of the BPMN 2. Activiti model. This can be done by following snippet of logic: 1. UUID id generator for high concurrency. In some (very) high concurrency load cases, the default id generator may cause exceptions due to not being able to fetch new id blocks quickly enough. Every process engine has one id generator. The default id generator reserves a block of ids in the database, such that no other engine will be able to use id’s from the same block. During engine operations, when the default id generator notices that the id block is used up, a new transaction is started to fetch a new block. In (very) limited use cases this can cause problems when there is a real high load. For most use cases the default id generator is more than sufficient. The default org. activiti. Db. Id. Generator also has a property id. Block. Size which can be configured to set the size of the reserved block of ids and to tweak the behavior of the id fetching. The alternative to the default id generator is the org. Strong. Uuid. Generator, which generates a unique UUID locally and uses that as identifier for all entities. Since the UUID is generated without the need for database access, it copes better with very high concurrency use cases. Do note that performance may differ from the default id generator (both positive and negative) depending on the machine. The UUID generator can be configured in the activiti configuration as follows: 1. Multitenancy. Multitenancy in general is a concept where the software is capable of serving multiple different organizations. Key is that the data is partitioned and no organization can see the data of other ones. In this context, such an organization (or a department, or a team or . Although Activiti is lightweight, and running a Process Engine instance doesn’t take much resources, it does add complexity and more maintenance. But, for some use cases it might be the right solution. Multitenancy in Activiti is mainly implemented around partitioning the data. It is important to note that Activiti does not enforce multi tenancy rules. This means it will not verify when querying and using data whether the user doing the operation is belonging to the correct tenant. This should be done in the layer calling the Activiti engine. Activiti does make sure that tenant information can be stored and used when retrieving process data. When deploying process definition to the Activiti Process Engine it is possible to pass a tenant identifier. This is a string (e. Standalone tasks can have a tenant identifier too. All executions created during process instance execution inherit this tenant identifier from the process instance. Firing a signal throw event (in the process itself or through the API) can be done whilst providing a tenant identifier. The signal will only be executed in the tenant context: i. This could potentially be used for giving priority to some tenants in a custom job executor. All the historic entities (historic process instance, task and activities) inherit the tenant identifier from their runtime counterparts. As a side note, models can have a tenant identifier too (models are used e. For example (and can be replaced by the relevant query implementation of the other entities): 1. Service. create. Process. Instance. Query(). Instance. Tenant. Id(. The combination of (process definition key, process definition version, tenant identifier) needs to be unique (and there is a database constraint checking this). Also note that the tenant identifier shouldn’t be set to null, as this will affect the queries since certain databases (Oracle) treat empty string as a null value (that’s why the query . Tenant. Id does a check against the empty string or null). This means that the same process definition (with same process definition key) can be deployed for multiple tenants, each with their own versioning. This does not affect the usage when tenancy is not used. Do note that all of the above does not conflict with running multiple Activiti instances in a cluster. This will change the tenant identifier everywhere it was inherited before. This can be useful when going from a non- multitenant setup to a multitenant configuration. See the Javadoc on the method for more detailed information. Execute custom SQLThe Activiti API allows for interacting with the database using a high level API. For example, for retrieving data the Query API and the Native Query API are powerful in its usage.
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