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HDFS-12251. Add document for StreamCapabilities. (Lei (Eddy) Xu) 

(cherry picked from commit fe3341786a)

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	hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSErasureCoding.md
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Lei Xu 2017-08-04 11:21:58 -07:00
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hadoop-common-project/hadoop-common/src/site/markdown/filesystem/filesystem.md
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@ -1199,3 +1199,27 @@ try {
It is notable that this is *not* done in the Hadoop codebase. This does not imply
that robust loops are not recommended —more that the concurrency
problems were not considered during the implementation of these loops.
## <a name="StreamCapability"></a> interface `StreamCapabilities`
The `StreamCapabilities` provides a way to programmatically query the
capabilities that an `OutputStream` supports.
```java
public interface StreamCapabilities {
boolean hasCapability(String capability);
}
```
### `boolean hasCapability(capability)`
Return true if the `OutputStream` has the desired capability.
The caller can query the capabilities of a stream using a string value.
It currently supports to query:
* `StreamCapabilties.HFLUSH` ("*hflush*"): the capability to flush out the data
in client's buffer.
* `StreamCapabilities.HSYNC` ("*hsync*"): capability to flush out the data in
client's buffer and the disk device.