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Gradle Task dependencies and ordering

In Gradle, tasks rarely exist in isolation; they often rely on the completion of other tasks or need to execute in a specific sequence to function correctly.^[600-developer__gradle__gradle-build.md] This relationship is managed through dependencies and ordering rules.

Task Dependencies

Task dependencies define a hard requirement where a task depends on the output or execution of another task.^[600-developer__gradle__gradle-build.md] When Task A depends on Task B, Gradle ensures Task B is executed successfully before Task A begins.^[600-developer__gradle__gradle-build.md]

You can define dependencies using the following syntax:

taskB.dependsOn taskA

This ensures that taskB will always wait for taskA to finish.^[600-developer__gradle__gradle-build.md]

Task Ordering

While dependencies enforce a strict "must run after" relationship, Gradle also provides mechanisms to order tasks without requiring them to succeed first.^[600-developer__gradle__gradle-build.md] This is useful for tasks that should occur logically after another but are not blocked by the other's failure.

mustRunAfter

The mustRunAfter method specifies that a task should be executed after another task, but it does not imply a dependency.^[600-developer__gradle__gradle-build.md] This means that if both tasks are scheduled to run, the ordering will be respected, but running the second task does not automatically force the first one to execute.

taskY.mustRunAfter taskX

This defines a strict ordering constraint that is enforced during the execution graph calculation.^[600-developer__gradle__gradle-build.md]

shouldRunAfter

The shouldRunAfter method suggests an ordering that is less strict than mustRunAfter.^[600-developer__gradle__gradle-build.md] It indicates a preference that a task run after another, but Gradle may ignore this rule if doing so would otherwise cause a cycle (circular dependency) in the execution graph.^[600-developer__gradle__gradle-build.md]

Task Inputs and Outputs

Gradle uses the concepts of inputs and outputs to determine if a task is up-to-date and to manage implicit dependencies.^[600-developer__gradle__gradle-build.md]

  • Inputs: Resources or files consumed by the task (e.g., source files).^[600-developer__gradle__gradle-build.md]
  • Outputs: Resources or files produced by the task (e.g., compiled classes or JARs).^[600-developer__gradle__gradle-build.md]

By defining these, Gradle can optimize the build by skipping tasks whose inputs haven't changed (UP-TO-DATE).^[600-developer__gradle__gradle-build.md]

inputs.files "path/to/input"
outputs.dir "path/to/output"
  • [[Gradle Build]]
  • [[Build lifecycle]]
  • [[Incremental build]]

Sources

  • gradle-build.md