org.elder.sourcerer.crud.CommandUtils Maven / Gradle / Ivy
package org.elder.sourcerer.crud;
import org.elder.sourcerer.CommandResponse;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.time.Duration;
import java.util.function.BiConsumer;
import java.util.function.Supplier;
/**
* Utility methods for constructing a synchronous facade from independent but related methods. Used
* to (re)create a traditional synchronous create/update operation on top of the command/query
* pattern by first executing the command, then waiting until the entity appears on the read side.
*/
public final class CommandUtils {
private static final Logger logger = LoggerFactory.getLogger(CommandUtils.class);
private CommandUtils() {
}
/**
* Waits for the presence of an entity in a read model, polling until the model asserts the
* presence of the entity at the given version.
*
* @param assertFunction A that should complete without exceptions if the relevant read model
* now has the entity with the given id and version. On any exception (but
* not other throwables), this method will be retried up to the maximum
* number of attempts specified, or until successful.
* @throws ReadAssertFailedException if the maximum number of retries have been attempted and
* the assertion still fails.
*/
public static void waitForUpdate(final Runnable assertFunction) {
waitForUpdate(
assertFunction,
Duration.ofMillis(50),
Duration.ofMillis(50),
1.5,
12);
}
/**
* Waits for the presence of an entity in a read model, polling until the model asserts the
* presence of the entity at the given version.
*
* @param assertFunction A that should complete without exceptions if the relevant read model
* now has the entity with the given id and version. On any exception
* (but not other throwables), this method will be retried up to the
* maximum number of attempts specified, or until successful.
* @param initialDelay The amount of time to wait between the command succeeding, and the
* first attempt to call the assert function.
* @param retryDelay The amount of time to wait after the first failed attempt to assert
* the presence of the aggregate, before retrying again.
* @param retryDelayFactor For exponential backoff - the factor to use to increase the delay
* between successive attempts. I.e. for a factor 2 and retry delay
* 100ms, the delays between attempts will be 100ms, 200ms, 400ms etc.
* @param maxRetryAttempts The maximum number of attempts before giving up on the operation.
* @throws ReadAssertFailedException if the maximum number of retries have been attempted and
* the assertion still fails.
*/
public static void waitForUpdate(
final Runnable assertFunction,
final Duration initialDelay,
final Duration retryDelay,
final double retryDelayFactor,
final int maxRetryAttempts) {
sleepSoundly(initialDelay.toMillis());
int attemptsLeft = maxRetryAttempts;
long currentSleepMillis = initialDelay.toMillis();
long currentRetryDelay = retryDelay.toMillis();
Exception lastAssertError = null;
do {
sleepSoundly(currentSleepMillis);
try {
assertFunction.run();
logger.debug("Assert successful");
return;
} catch (Exception ex) {
logger.debug("Assert failed: {}", ex.getMessage());
lastAssertError = ex;
currentSleepMillis = (long) (currentRetryDelay * retryDelayFactor);
currentRetryDelay = currentSleepMillis;
attemptsLeft--;
}
}
while (attemptsLeft > 0);
logger.warn(
"Retries exhausted after {} attempts, last error:",
maxRetryAttempts,
lastAssertError);
throw new ReadAssertFailedException(lastAssertError);
}
/**
* Executes a command, and waits for the affected entity to be updated in the relevant read
* model. This method will execute the command once, propagating any exceptions immediately. If
* the command is successful, it will use the provided assert function to check that it has been
* created, retrying periodically as required until completed.
*
* @param commandFunction A function that, when called, executes the command and returns the id
* of the affected entity along with its new version.
* @param assertFunction A function accepting an aggregate id and version that should complete
* without exceptions if the relevant read model now has the entity with
* the given id and version. On any exception (but not other throwables),
* this method will be retried up to the maximum number of attempts
* specified, or until successful.
* @return The command response as returned from the command function.
* @throws ReadAssertFailedException if the maximum number of retries have been attempted and
* the assertion still fails.
*/
public static CommandResponse executeSynchronously(
final Supplier commandFunction,
final BiConsumer assertFunction) {
return executeSynchronously(
commandFunction,
assertFunction,
Duration.ofMillis(50),
Duration.ofMillis(50),
1.5,
12);
}
/**
* Executes a command, and waits for the affected entity to be updated in the relevant read
* model. This method will execute the command once, propagating any exceptions immediately. If
* the command is successful, it will use the provided assert function to check that it has been
* created, retrying periodically as required until completed.
*
* @param commandFunction A function that, when called, executes the command and returns the id
* of the affected entity along with its new version.
* @param assertFunction A function accepting an aggregate id and version that should complete
* without exceptions if the relevant read model now has the entity with
* the given id and version. On any exception (but not other
* throwables), this method will be retried up to the maximum number of
* attempts specified, or until successful.
* @param initialDelay The amount of time to wait between the command succeeding, and the
* first attempt to call the assert function.
* @param retryDelay The amount of time to wait after the first failed attempt to assert
* the presence of the aggregate, before retrying again.
* @param retryDelayFactor For exponential backoff - the factor to use to increase the delay
* between successive attempts. I.e. for a factor 2 and retry delay
* 100ms, the delays between attempts will be 100ms, 200ms, 400ms etc.
* @param maxRetryAttempts The maximum number of attempts before giving up on the operation.
* @return The command response as returned from the command function.
* @throws ReadAssertFailedException if the maximum number of retries have been attempted and
* the assertion still fails.
*/
public static CommandResponse executeSynchronously(
final Supplier commandFunction,
final BiConsumer assertFunction,
final Duration initialDelay,
final Duration retryDelay,
final double retryDelayFactor,
final int maxRetryAttempts) {
CommandResponse commandResponse = commandFunction.get();
if (commandResponse.getNoOp() != null && commandResponse.getNoOp()) {
logger.debug("Command was no-op, not waiting around");
return commandResponse;
}
int expectedVersion;
if (commandResponse.getPreviousVersion() != null) {
expectedVersion = commandResponse.getPreviousVersion() + 1;
logger.debug("Looking for version {} based on previous", expectedVersion);
} else if (commandResponse.getNewVersion() != null) {
expectedVersion = commandResponse.getNewVersion();
logger.debug("Looking for version {} based on new", expectedVersion);
} else {
throw new IllegalArgumentException("Command was not no-op but returned no version!");
}
waitForUpdate(
() -> assertFunction.accept(commandResponse.getId(), expectedVersion),
initialDelay,
retryDelay,
retryDelayFactor,
maxRetryAttempts);
return commandResponse;
}
private static void sleepSoundly(final long millis) {
try {
Thread.sleep(millis);
} catch (InterruptedException ex) {
logger.warn("Interrupted while sleeping, ignoring");
}
}
}
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