分析你的系統(tǒng)

你所認(rèn)識(shí)的分布式系統(tǒng)，哪些是可以進(jìn)行垂直拆分的？拆分之后系統(tǒng)之間的依賴如何梳理？系統(tǒng)異構(gòu)之后的穩(wěn)定性調(diào)用如何保證？這些都是可能在分布式場(chǎng)景中面臨的問題。

說個(gè)比較常見的問題，大家都知道秒殺系統(tǒng)，秒殺流程在分布式的環(huán)境中，就需要依賴：訂單管理，會(huì)員管理，支付等，假如在整個(gè)系統(tǒng)中會(huì)員系統(tǒng)不穩(wěn)定，導(dǎo)致系統(tǒng)請(qǐng)求擠壓，慢慢的就會(huì)導(dǎo)致對(duì)其他外部系統(tǒng)的依賴也不可用，所以就要使用業(yè)務(wù)的隔離，這樣會(huì)避免服務(wù)的局部不可用導(dǎo)致的全部不可用。

Hystrix 源碼分析

找到HystrixCommand的父類AbstractCommand， 里面有個(gè)構(gòu)造方法，從構(gòu)造方法可以看出里這里定義了 threadPool對(duì)象。代碼如下，關(guān)鍵代碼都有做相應(yīng)的注釋。

protected AbstractCommand(HystrixCommandGroupKey group, HystrixCommandKey key, HystrixThreadPoolKey threadPoolKey, HystrixCircuitBreaker circuitBreaker, HystrixThreadPool threadPool,

HystrixCommandProperties.Setter commandPropertiesDefaults, HystrixThreadPoolProperties.Setter threadPoolPropertiesDefaults,

HystrixCommandMetrics metrics, TryableSemaphore fallbackSemaphore, TryableSemaphore executionSemaphore,

HystrixPropertiesStrategy propertiesStrategy, HystrixCommandExecutionHook executionHook) {

//commandGroup對(duì)象，用于組織一類業(yè)務(wù)相關(guān)的對(duì)象

this.commandGroup = initGroupKey(group);

// commandKey默認(rèn)是以類為為名稱的

this.commandKey = initCommandKey(key, getClass());

this.properties = initCommandProperties(this.commandKey, propertiesStrategy, commandPropertiesDefaults);

//這個(gè)方法里定義了TheradPool里的關(guān)鍵字，默認(rèn)以傳入的commandGroup 的name做為key的名稱

this.threadPoolKey = initThreadPoolKey(threadPoolKey, this.commandGroup, this.properties.executionIsolationThreadPoolKeyOverride().get());

this.metrics = initMetrics(metrics, this.commandGroup, this.threadPoolKey, this.commandKey, this.properties);

this.circuitBreaker = initCircuitBreaker(this.properties.circuitBreakerEnabled().get(), circuitBreaker, this.commandGroup, this.commandKey, this.properties, this.metrics);

//這里就是線程池對(duì)象啦。

this.threadPool = initThreadPool(threadPool, this.threadPoolKey, threadPoolPropertiesDefaults);

//Strategies from plugins

this.eventNotifier = HystrixPlugins.getInstance().getEventNotifier();

this.concurrencyStrategy = HystrixPlugins.getInstance().getConcurrencyStrategy();

HystrixMetricsPublisherFactory.createOrRetrievePublisherForCommand(this.commandKey, this.commandGroup, this.metrics, this.circuitBreaker, this.properties);

this.executionHook = initExecutionHook(executionHook);

this.requestCache = HystrixRequestCache.getInstance(this.commandKey, this.concurrencyStrategy);

this.currentRequestLog = initRequestLog(this.properties.requestLogEnabled().get(), this.concurrencyStrategy);

/* fallback semaphore override if applicable */

this.fallbackSemaphoreOverride = fallbackSemaphore;

/* execution semaphore override if applicable */

this.executionSemaphoreOverride = executionSemaphore;

}

/**

這個(gè)方法用于得到HystrixThreadPoolKey 對(duì)象， Hystrix內(nèi)部有大量的Key對(duì)象，可以簡(jiǎn)單理解這些 Key都是相應(yīng)對(duì)象的唯一標(biāo)識(shí)。從代碼里可以看出，默認(rèn)情況下Hystrix采用的是commandGroup 的name做為Thread Pool的key值。

**/

private static HystrixThreadPoolKey initThreadPoolKey(HystrixThreadPoolKey threadPoolKey, HystrixCommandGroupKey groupKey, String threadPoolKeyOverride) {

if (threadPoolKeyOverride == null) {

// we don't have a property overriding the value so use either HystrixThreadPoolKey or HystrixCommandGroup

if (threadPoolKey == null) {

/* use HystrixCommandGroup if HystrixThreadPoolKey is null */

return HystrixThreadPoolKey.Factory.asKey(groupKey.name());

} else {

return threadPoolKey;

}

} else {

// we have a property defining the thread-pool so use it instead

return HystrixThreadPoolKey.Factory.asKey(threadPoolKeyOverride);

}

}

/**

在這里將調(diào)用具體的構(gòu)造線程池的方法。

**/

private static HystrixThreadPool initThreadPool(HystrixThreadPool fromConstructor, HystrixThreadPoolKey threadPoolKey, HystrixThreadPoolProperties.Setter threadPoolPropertiesDefaults) {

if (fromConstructor == null) {

// get the default implementation of HystrixThreadPool

return HystrixThreadPool.Factory.getInstance(threadPoolKey, threadPoolPropertiesDefaults);

} else {

return fromConstructor;

}

}

總結(jié)

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