UP-TO-DATE Checks (Task Avoidance)

Gradle uses up-to-date checks as a mechanism to avoid re-executing tasks unnecessarily, optimizing the build process and reducing execution time. Before executing a task, Gradle checks whether the task is up-to-date by comparing the task's inputs and outputs. If none of the inputs or outputs have changed, the task is considered up-to-date, and Gradle skips its execution.

Example output

Example how gradle shows that a task was skipped because it was up-to-date (refer to To Add More Output (Gradle Arguments) to see such output):

Task :lib:processData UP-TO-DATE

How Up-to-date Checks Work:

• Gradle tracks the inputs (files, Properties (Gradle), etc.) and outputs (generated files, artifacts) of each task.
• If the inputs haven’t changed and the outputs haven't changed, Gradle considers the task up-to-date and does not execute it. Gradle uses the hashes of the inputs and outputs to determine if they have changed. (Gradle Checks Hashes of Output Files)
• This feature improves build times by preventing tasks from running unnecessarily.

Gotcha:

• Environment Variables (In Gradle) and System Property (in Gradle) are not tracked by Gradle and can cause tasks to be skipped unintentionally.

Example of Up-to-date Checks:

tasks.register("processData") {
    // Declare input and output for the task
    inputs.file("src/data/input.txt")   // Input file
    outputs.file("build/output.txt")    // Output file

    doLast {
        println("doLast Task executing, Processing input...")
        val inputFile = file("src/data/input.txt")
        val outputFile = file("build/output.txt")
        outputFile.writeText("""${Instant.now()} ${inputFile.readText().toUpperCase()}""")
        println("Task executed: Input processed.")
    }
}

gt.sandbox.checkout.commit b0d1f9a \
&& cd "${GT_SANDBOX_REPO}" \
&& cmd.run.announce "./gradlew lib:processData --console=plain && echo && echo output.txt: && cat ${GLASSTHOUGHT_SANDBOX:?}/lib/build/output.txt"

> Task :lib:processData UP-TO-DATE

BUILD SUCCESSFUL in 409ms
1 actionable task: 1 up-to-date

output.txt:
2024-10-05T22:17:27.708102Z VAL-2

In this example:

• Input: The file src/data/input.txt is declared as the input.
• Output: The file build/output.txt is declared as the output.
• When Gradle runs the task, it checks whether the input or output has changed. If the input file is unchanged and the output file already exists with the correct content, Gradle will skip re-executing the task and consider it up-to-date.