top -Hp {pid}
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java/bin/jstat -gcutil {pid} 1000
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    // 默认缓存大小
    private final static int DEFAULT_MAX_CACHE_SIZE = 20480;

    // package private
    SSLSessionContextImpl() {
        cacheLimit = getDefaultCacheLimit();    // default cache size，这里默认是20480
        timeout = 86400;                        // default, 24 hours

        // use soft reference
        // 这里初始化了2个默认大小20480的缓存，是频繁GC的原因
        sessionCache = Cache.newSoftMemoryCache(cacheLimit, timeout);
        sessionHostPortCache = Cache.newSoftMemoryCache(cacheLimit, timeout);
    }

    // 获取默认缓存大小
    private static int getDefaultCacheLimit(){
        try {
            int defaultCacheLimit = GetIntegerAction.privilegedGetProperty(
                    "javax.net.ssl.sessionCacheSize", DEFAULT_MAX_CACHE_SIZE);

            if (defaultCacheLimit >= 0) {
                return defaultCacheLimit;
            } else if (SSLLogger.isOn && SSLLogger.isOn("ssl")) {
                SSLLogger.warning(
                    "invalid System Property javax.net.ssl.sessionCacheSize, " +
                    "use the default session cache size (" +
                    DEFAULT_MAX_CACHE_SIZE + ") instead");
            }
        } catch (Exception e) {
            // unlikely, log it for safe
            if (SSLLogger.isOn && SSLLogger.isOn("ssl")) {
                SSLLogger.warning(
                    "the System Property javax.net.ssl.sessionCacheSize is " +
                    "not available, use the default value (" +
                    DEFAULT_MAX_CACHE_SIZE + ") instead");
            }
        }

        return DEFAULT_MAX_CACHE_SIZE;
    }
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httpclient.reset_state_on_thread_group_iteration=false
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     /**
     *  Whether SSL State/Context should be reset
     *  Shared state for any HC based implementation, because SSL contexts are the same 
     */
    protected static final ThreadLocal<Boolean> resetStateOnThreadGroupIteration =
            ThreadLocal.withInitial(() -> Boolean.FALSE);


    /**
     * Reset SSL State. <br/>
     * In order to do that we need to:
     * <ul>
     *  <li>Call resetContext() on SSLManager</li>
     *  <li>Close current Idle or Expired connections that hold SSL State</li>
     *  <li>Remove HttpClientContext.USER_TOKEN from {@link HttpClientContext}</li>
     * </ul>
     * @param jMeterVariables {@link JMeterVariables}
     * @param clientContext {@link HttpClientContext}
     * @param mapHttpClientPerHttpClientKey Map of {@link Pair} holding {@link CloseableHttpClient} and {@link
    private void resetStateIfNeeded(JMeterVariables jMeterVariables, 
            HttpClientContext clientContext,
            Map<HttpClientKey, Pair<CloseableHttpClient, PoolingHttpClientConnectionManager>> mapHttpClientPerHttpClientKey){
        if (resetStateOnThreadGroupIteration.get()) {
            // 关闭当前线程对应连接池的超时、空闲连接，重置连接池状态
            closeCurrentConnections(mapHttpClientPerHttpClientKey);
            // 移除Token
            clientContext.removeAttribute(HttpClientContext.USER_TOKEN);
            // 重置SSL上下文
            ((JsseSSLManager) SSLManager.getInstance()).resetContext();
            // 标记置为false，保证一次循环中，只有第一个采样器走进此逻辑
            resetStateOnThreadGroupIteration.set(false);
        }
    }

    @Override
    protected void notifyFirstSampleAfterLoopRestart(){
        log.debug("notifyFirstSampleAfterLoopRestart called "
                + "with config(httpclient.reset_state_on_thread_group_iteration={})",
                RESET_STATE_ON_THREAD_GROUP_ITERATION);
        resetStateOnThreadGroupIteration.set(RESET_STATE_ON_THREAD_GROUP_ITERATION);
    }
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