问题

我有一段代码：

rows = types.stream().parallel().map(s -> {
    switch (s){
        case NDBaseDocumentModel.DOC_TYPE_NSS:
            return getDocsOfSpecificTypeAndCountItsDupes(NDGostStandardsModel.TYPE_ND_GOST_STANDARDS, null,systemMessages.getString("form20.nss.name")).values();
        case NDBaseDocumentModel.DOC_INT_REG_STANDARDS:
            return getDocsOfSpecificTypeAndCountItsDupes(NDIntRegStandardsModel.TYPE_ND_INT_REG_STANDARDS, null,systemMessages.getString("form20.int_reg")).values();
    }
    return new HashSet<Form20Row>();
}).flatMap(o -> {
    return o.stream();
}).collect(Collectors.toList());

而且它不起作用（返回零行），但是当我移除 "parallel()" 调用时可以正常工作（相同数据上的 14 行）。有人可以告诉我为什么吗？拜托。
拜托？


<details>
<summary>英文:</summary>

I have a code :

    rows = types.stream().parallel().map(s -&gt; {
        switch (s){
            case NDBaseDocumentModel.DOC_TYPE_NSS:
                return getDocsOfSpecificTypeAndCountItsDupes(NDGostStandardsModel.TYPE_ND_GOST_STANDARDS, null,systemMessages.getString(&quot;form20.nss.name&quot;)).values();
            case NDBaseDocumentModel.DOC_INT_REG_STANDARDS:
                return getDocsOfSpecificTypeAndCountItsDupes(NDIntRegStandardsModel.TYPE_ND_INT_REG_STANDARDS, null,systemMessages.getString(&quot;form20.int_reg&quot;)).values();
        }
        return new HashSet&lt;Form20Row&gt;();
    }).flatMap(o -&gt; {
        return o.stream();
    }).collect(Collectors.toList());

And it doesn&#39;t work (return zero rows), but work fine when I remove &quot;parallel()&quot; call (14 rows on same data). Could somebody tell me why, please??
Please?

</details>


# 答案1
**得分**: 1

并行流程使用线程池进行处理，因此您的方法`getDocsOfSpecificTypeAndCountItsDupes`需要是线程安全的。

如果移除`parallel()`并在同一线程上处理，可以解决您的问题，因此似乎该方法中有一些不是线程安全的内容，这可能是您的问题。

<details>
<summary>英文:</summary>

Parallel streams are processed using a thread pool, and as such your method `getDocsOfSpecificTypeAndCountItsDupes` needs to be thread-safe.

As removing the `parallel()` and processing it on the same thread fixes your issue, it seems likely that there&#39;s something in the method that isn&#39;t thread-safe, which will be your problem.

</details>