auth/src/main/java/org/apache/rocketmq/auth/authorization/factory/AuthorizationFactory.java [136:155]:
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    private static <V> V computeIfAbsent(String key, Function<String, ? extends V> function) {
        Object result = null;
        if (INSTANCE_MAP.containsKey(key)) {
            result = INSTANCE_MAP.get(key);
        }
        if (result == null) {
            synchronized (INSTANCE_MAP) {
                if (INSTANCE_MAP.containsKey(key)) {
                    result = INSTANCE_MAP.get(key);
                }
                if (result == null) {
                    result = function.apply(key);
                    if (result != null) {
                        INSTANCE_MAP.put(key, result);
                    }
                }
            }
        }
        return result != null ? (V) result : null;
    }
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auth/src/main/java/org/apache/rocketmq/auth/authentication/factory/AuthenticationFactory.java [133:152]:
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    private static <V> V computeIfAbsent(String key, Function<String, ? extends V> function) {
        Object result = null;
        if (INSTANCE_MAP.containsKey(key)) {
            result = INSTANCE_MAP.get(key);
        }
        if (result == null) {
            synchronized (INSTANCE_MAP) {
                if (INSTANCE_MAP.containsKey(key)) {
                    result = INSTANCE_MAP.get(key);
                }
                if (result == null) {
                    result = function.apply(key);
                    if (result != null) {
                        INSTANCE_MAP.put(key, result);
                    }
                }
            }
        }
        return result != null ? (V) result : null;
    }
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