一、dubbo提供6种容错模式
- failover：默认模式。调用失败时，自动切换重试，可通过retries属性设置重试次数。适用于读操作，每次读数据都相同。
- failfast：快速失败模式。只调用一次，调用失败时立即报错。适用于写操作，不能重复写。
- failsafe：安全失败模式。只调用一次，调用失败时忽略失败的调用，记录日志。
- failback：失败恢复模式。在失败后自动恢复，后台记录失败的请求，定时重发。通常用于消息通知。
- forking：并行调用多个服务器，只要有一个成功便返回。通常用于实时性要求较高的读操作，会浪费服务资源。
- broadcast：广播调用所有的提供者，逐个调用，任意一台报错则报错。通常用于通知所有提供者更新缓存或日志等本地资源信息。
二、FailOverClusterInvoker——失败重试
/* org.apache.dubbo.rpc.cluster.support.FailoverClusterInvoker */
public Result doInvoke(Invocation invocation, final List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
List<Invoker<T>> copyInvokers = invokers;
//检查providers不能为空
checkInvokers(copyInvokers, invocation);
//获取调用的方法名
String methodName = RpcUtils.getMethodName(invocation);
//调用次数 1+2次重试
int len = getUrl().getMethodParameter(methodName, RETRIES_KEY, DEFAULT_RETRIES) + 1;
if (len <= 0) {
len = 1;
}
// retry loop.
RpcException le = null; // last exception.
List<Invoker<T>> invoked = new ArrayList<Invoker<T>>(copyInvokers.size()); // invoked invokers.
Set<String> providers = new HashSet<String>(len);
for (int i = 0; i < len; i++) {
//失败重试，成功返回
if (i > 0) {
//再次检查invokers.destroyed
checkWhetherDestroyed();
copyInvokers = list(invocation);
// check again
checkInvokers(copyInvokers, invocation);
}
//负载均衡策略，选取一个invoker
Invoker<T> invoker = select(loadbalance, invocation, copyInvokers, invoked);
//标记已经调用过的invoker，重试时，换其他invoker重试
invoked.add(invoker);
RpcContext.getContext().setInvokers((List) invoked);
try {
Result result = invoker.invoke(invocation);
if (le != null && logger.isWarnEnabled()) {
logger.warn("Although retry the method " + methodName
+ " in the service " + getInterface().getName()
+ " was successful by the provider " + invoker.getUrl().getAddress()
+ ", but there have been failed providers " + providers
+ " (" + providers.size() + "/" + copyInvokers.size()
+ ") from the registry " + directory.getUrl().getAddress()
+ " on the consumer " + NetUtils.getLocalHost()
+ " using the dubbo version " + Version.getVersion() + ". Last error is: "
+ le.getMessage(), le);
}
//成功返回
return result;
//catch报错，失败重试
} catch (RpcException e) {
if (e.isBiz()) { // biz exception.
throw e;
}
le = e;
} catch (Throwable e) {
le = new RpcException(e.getMessage(), e);
} finally {
providers.add(invoker.getUrl().getAddress());
}
}
throw new RpcException(le.getCode(), "Failed to invoke the method "
+ methodName + " in the service " + getInterface().getName()
+ ". Tried " + len + " times of the providers " + providers
+ " (" + providers.size() + "/" + copyInvokers.size()
+ ") from the registry " + directory.getUrl().getAddress()
+ " on the consumer " + NetUtils.getLocalHost() + " using the dubbo version "
+ Version.getVersion() + ". Last error is: "
+ le.getMessage(), le.getCause() != null ? le.getCause() : le);
}
三、FailfastClusterInvoker——失败抛错
/* org.apache.dubbo.rpc.cluster.support.FailfastClusterInvoker#doInvoke */
public Result doInvoke(Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
//检查invokers不能为空
checkInvokers(invokers, invocation);
//负载均衡策略，选取一个invoker
Invoker<T> invoker = select(loadbalance, invocation, invokers, null);
try {
//调用
return invoker.invoke(invocation);
} catch (Throwable e) {
//调用失败直接抛错
if (e instanceof RpcException && ((RpcException) e).isBiz()) { // biz exception.
throw (RpcException) e;
}
throw new RpcException(e instanceof RpcException ? ((RpcException) e).getCode() : 0,
"Failfast invoke providers " + invoker.getUrl() + " " + loadbalance.getClass().getSimpleName()
+ " select from all providers " + invokers + " for service " + getInterface().getName()
+ " method " + invocation.getMethodName() + " on consumer " + NetUtils.getLocalHost()
+ " use dubbo version " + Version.getVersion()
+ ", but no luck to perform the invocation. Last error is: " + e.getMessage(),
e.getCause() != null ? e.getCause() : e);
}
}
四、FaisafeClusterInvoker——失败忽略，记录日志
/* org.apache.dubbo.rpc.cluster.support.FailsafeClusterInvoker#doInvoke */
public Result doInvoke(Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
try {
//检查invokers不能为空
checkInvokers(invokers, invocation);
//负载均衡策略，选取一个invoker
Invoker<T> invoker = select(loadbalance, invocation, invokers, null);
//调用
return invoker.invoke(invocation);
} catch (Throwable e) {
//报错忽略
logger.error("Failsafe ignore exception: " + e.getMessage(), e);
return AsyncRpcResult.newDefaultAsyncResult(null, null, invocation); // ignore
}
}
五、FailbackClusterInvoker——失败恢复，记录失败请求，定时重发
/* org.apache.dubbo.rpc.cluster.support.FailbackClusterInvoker#doInvoke */
protected Result doInvoke(Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
Invoker<T> invoker = null;
try {
//检查invokers不能为空
checkInvokers(invokers, invocation);
//负载均衡策略，选取一个invoker
invoker = select(loadbalance, invocation, invokers, null);
//调用
return invoker.invoke(invocation);
} catch (Throwable e) {
//失败忽略
logger.error("Failback to invoke method " + invocation.getMethodName() + ", wait for retry in background. Ignored exception: "
+ e.getMessage() + ", ", e);
//创建定时任务TimeTask实现
addFailed(loadbalance, invocation, invokers, invoker);
//返回记录失败日志
return AsyncRpcResult.newDefaultAsyncResult(null, null, invocation); // ignore
}
}
六、ForkingClusterInvoker——并行调用，有一个调用成功便返回
/* org.apache.dubbo.rpc.cluster.support.ForkingClusterInvoker#doInvoke */
public Result doInvoke(final Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
try {
//检查invokers不能为空
checkInvokers(invokers, invocation);
final List<Invoker<T>> selected;
final int forks = getUrl().getParameter(FORKS_KEY, DEFAULT_FORKS);
final int timeout = getUrl().getParameter(TIMEOUT_KEY, DEFAULT_TIMEOUT);
if (forks <= 0 || forks >= invokers.size()) {
//并发数forks大于invokers.size()时，并发调用所有invoker
selected = invokers;
} else {
//并发数forks小于invokers.size()时，调用负载均衡策略选取的forks个invoker
selected = new ArrayList<>();
for (int i = 0; i < forks; i++) {
Invoker<T> invoker = select(loadbalance, invocation, invokers, selected);
if (!selected.contains(invoker)) {
//Avoid add the same invoker several times.
selected.add(invoker);
}
}
}
RpcContext.getContext().setInvokers((List) selected);
final AtomicInteger count = new AtomicInteger();
final BlockingQueue<Object> ref = new LinkedBlockingQueue<>();
for (final Invoker<T> invoker : selected) {
executor.execute(() -> {
try {
//并发调用，报错忽略
Result result = invoker.invoke(invocation);
//创建一个队列，存储返回结果
ref.offer(result);
} catch (Throwable e) {
int value = count.incrementAndGet();
if (value >= selected.size()) {
ref.offer(e);
}
}
});
}
try {
//取队首元素（结果），设置超时时间
Object ret = ref.poll(timeout, TimeUnit.MILLISECONDS);
if (ret instanceof Throwable) {
//正常的报错抛出错误
Throwable e = (Throwable) ret;
throw new RpcException(e instanceof RpcException ? ((RpcException) e).getCode() : 0, "Failed to forking invoke provider " + selected + ", but no luck to perform the invocation. Last error is: " + e.getMessage(), e.getCause() != null ? e.getCause() : e);
}
//调用成功返回
return (Result) ret;
} catch (InterruptedException e) {
//超时抛错
throw new RpcException("Failed to forking invoke provider " + selected + ", but no luck to perform the invocation. Last error is: " + e.getMessage(), e);
}
} finally {
// clear attachments which is binding to current thread.
RpcContext.getContext().clearAttachments();
}
}
七、BroadcastClusterInvoker——串行调用，所有调用成功则成功，有一台报错则抛错
/* org.apache.dubbo.rpc.cluster.support.BroadcastClusterInvoker#doInvoke */
public Result doInvoke(final Invocation invocation, List<Invoker<T>> invokers, LoadBalance loadbalance) throws RpcException {
//检查invokers不能为空
checkInvokers(invokers, invocation);
RpcContext.getContext().setInvokers((List) invokers);
RpcException exception = null;
Result result = null;
for (Invoker<T> invoker : invokers) {
try {
//遍历调用
result = invoker.invoke(invocation);
} catch (RpcException e) {
exception = e;
logger.warn(e.getMessage(), e);
} catch (Throwable e) {
exception = new RpcException(e.getMessage(), e);
logger.warn(e.getMessage(), e);
}
}
//有一个invoker调用抛错，则抛出错误
if (exception != null) {
throw exception;
}
return result;
}
