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From "James Clampffer (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-10188) libhdfs++: Implement debug allocators
Date Wed, 18 May 2016 19:41:12 GMT

     [ https://issues.apache.org/jira/browse/HDFS-10188?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel

James Clampffer updated HDFS-10188:
    Attachment: HDFS-10188.HDFS-8707.004.patch

New patch looks good, I went to fix a typo where it was doing something like
  memset(ptr, 0, sizeof(ptr))
and tried to change to
  memset(ptr, 0, sizeof(decltype(this)))

I forgot that member new/delete needed to be static, and because of that they don't get to
see 'this', so sizeof(decltype(this)) doesn't compile.  Sorry for the bad advice there.

The quick fix was to pass in the class name as a macro argument; not ideal but not terrible.
 The API would look like
class UsedAfterFreeSometimes {
Unfortunately it looks like getting an implicit typename isn't really possible in static methods
short of even more macro tricks.

Xiaowei, could you take a look at these changes and see if they are still in line with what
you did?

> libhdfs++: Implement debug allocators
> -------------------------------------
>                 Key: HDFS-10188
>                 URL: https://issues.apache.org/jira/browse/HDFS-10188
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs-client
>            Reporter: James Clampffer
>            Assignee: Xiaowei Zhu
>         Attachments: HDFS-10188.HDFS-8707.000.patch, HDFS-10188.HDFS-8707.001.patch,
HDFS-10188.HDFS-8707.002.patch, HDFS-10188.HDFS-8707.003.patch, HDFS-10188.HDFS-8707.004.patch
> I propose implementing a set of memory new/delete pairs with additional checking to detect
double deletes, read-after-delete, and write-after-deletes to help debug resource ownership
issues and prevent new ones from entering the library.
> One of the most common issues we have is use-after-free issues.  The continuation pattern
makes these really tricky to debug because by the time a segsegv is raised the context of
what has caused the error is long gone.
> The plan is to add allocators that can be turned on that can do the following, in order
of runtime cost.
> 1: no-op, forward through to default new/delete
> 2: make sure the memory given to the constructor is dirty, memset free'd memory to 0
> 3: implement operator new with mmap, lock that region of memory once it's been deleted;
obviously this can't be left to run forever because the memory is never unmapped
> This should also put some groundwork in place for implementing specialized allocators
for tiny objects that we churn through like std::string.

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