WorkManager 的 OneTimeWorkRequest 的重试策略/机制是什么

Question

我有以下的临时工

// Create a Constraints that defines when the task should run
Constraints constraints = new Constraints.Builder()
        .setRequiredNetworkType(NetworkType.UNMETERED)
        .setRequiresBatteryNotLow(true)
        // Many other constraints are available, see the
        // Constraints.Builder reference
        .build();

OneTimeWorkRequest oneTimeWorkRequest =
        new OneTimeWorkRequest.Builder(SyncWorker.class)
                .setConstraints(constraints)
                .addTag(SyncWorker.TAG)
                .build();

根据https://developer.android.com/topic/libraries/architecture/workmanager

// (Returning RETRY tells WorkManager to try this task again
// later; FAILURE says not to try again.)

我在想，如果SyncWorker一直返回RETRY，WorkManager的重试策略是什么？例如，WorkManager 的最大重试次数是多少？文档对此并不清楚。

Answer 1

默认为BackoffPolicy.EXPONENTIAL。我们仅在您通过返回 WorkerResult.RETRY 要求我们 RETRY 时或当您的 Worker 所需的约束现在未满足时才重试。所以例如如果您需要 NETWORK 约束，现在设备丢失了其活动的 Network 连接 - 那么 Worker 将停止并自动重试（当满足约束时）。

有关详细信息，请查看 docs。

Answer 2

下面的示例在退出前在捕捉到异常时重试 3 次。

class RepeatWorker(context : Context, params : WorkerParameters)
    : Worker(context, params) {

    private fun doSomeThing() {
        // do something
    }

    override fun doWork(): Result {

        if (runAttemptCount > 3) {
            return Result.failure()
        }

        try {
            doSomeThing()
        }
        catch (e: Exception) {
            e.printStackTrace()
            return Result.retry()
        }
        return Result.success()
    }
}

注意：默认 BackoffPolicy 是指数的，其中 30 秒后第一次重试（最短重试周期为 10 秒，最大重试周期不超过 18000 秒/5 小时）。

fun start() : LiveData<WorkInfo> {
    val WORK_NAME = "SingleBackupWorker"

    val constraints = Constraints.Builder()
            .setRequiredNetworkType(NetworkType.CONNECTED)
            .build()

    val work = OneTimeWorkRequestBuilder<BackupWorker>()
            .setConstraints(constraints)
            .setInitialDelay(5, TimeUnit.SECONDS)
            .setBackoffCriteria(BackoffPolicy.EXPONENTIAL, 1, TimeUnit.MINUTES)
            .build()

    WorkManager.getInstance().enqueueUniqueWork(WORK_NAME, ExistingWorkPolicy.REPLACE, work)

    return WorkManager.getInstance().getWorkInfoByIdLiveData(work.id)
}

Answer 3

从 runAttemptCount 获取任何工作的当前运行尝试计数。请注意，对于周期性工作，此值会在周期之间重置。 Link:-

https://developer.android.com/reference/androidx/work/ListenableWorker#getRunAttemptCount()

示例：

override fun doWork(): Result {

    if (runAttemptCount < maxRetryConstantIWant) {
    ..... 
    .....
    .....
    } else { Result.Failure }
}

这里runAttemptCount是worker方法

WorkManager 的 OneTimeWorkRequest 的重试策略/机制是什么

What are the retry strategy/ mechanism for WorkManager's OneTimeWorkRequest

android

android-architecture-components

android-workmanager