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https://issues.apache.org/jira/browse/HDFS-8766?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14905406#comment-14905406
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Haohui Mai commented on HDFS-8766:
----------------------------------
Thanks for the work.
It looks like that the code needs a lot of clean ups. The code needs to follow
the Google C++ styling guide and be formatted using clang-format.
I think it's important to have several abstractions. There should be C++
classes that correspond FileSystem / FileHandle as Bob mentioned.
{code}
+ ssize_t pread(void *buf, size_t nbyte, off_t offset) {
+ auto stat = std::make_shared<std::promise<Status>>();
+ std::future<Status> future(stat->get_future());
+
+ //wrap async call with promise/future to make it blocking
+ size_t readCount = 0;
+ std::string datanode;
+ auto h = [stat, &readCount, &datanode](const Status &s, const std::string
&dn, size_t bytes) {
+ stat->set_value(s);
+ readCount = bytes;
+ datanode = dn;
+ };
+
+ inputStream->PositionRead(buf, nbyte, offset, bad_datanodes, h);
+
+ //wait for async to finish
+ auto s = future.get();
+
+ if(!s.ok()) {
+ //for now assume this was a down DN, not going to reinvent HDFS-9103
+ if(s.code() == Status::kResourceUnavailable) {
+ errno = ECOMM;
+ bad_datanodes.insert(datanode);
+ }
+ //otherwise it was a real error so indicate that something's gone wrong
+ return -1;
+ }
{code}
It should be a generic template to abstract the operations of wrapping async
calls to synchronous calls.
> Implement a libhdfs(3) compatible API
> -------------------------------------
>
> Key: HDFS-8766
> URL: https://issues.apache.org/jira/browse/HDFS-8766
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: hdfs-client
> Reporter: James Clampffer
> Assignee: James Clampffer
> Attachments: HDFS-8766.HDFS-8707.000.patch
>
>
> Add a synchronous API that is compatible with the hdfs.h header used in
> libhdfs and libhdfs3. This will make it possible for projects using
> libhdfs/libhdfs3 to relink against libhdfspp with minimal changes.
> This also provides a pure C interface that can be linked against projects
> that aren't built in C++11 mode for various reasons but use the same
> compiler. It also allows many other programming languages to access
> libhdfspp through builtin FFI interfaces.
> The libhdfs API is very similar to the posix file API which makes it easier
> for programs built using posix filesystem calls to be modified to access HDFS.
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