6709457: (fc) lock/tryLock() throws IOException "Access is denied" when file opened for append [win]

Alan Bateman Alan.Bateman at oracle.com
Mon Nov 29 11:25:15 UTC 2010

This is an awkward regression that Martin and I previously discussed on 
this list [1].

To re-cap: When the redirection API for sub-processes was added early in 
jdk7, FileOutputStream was changed on Windows so that opening a file in 
append mode results in the write-at-end to be atomic. It achieves this 
by opening the file with FILE_APPEND_DATA and not FILE_WRITE_DATA 
access. Unfortunately this change came with side effects, the main one 
being that it breaks the file locking facility for files opened for 
append. We also observed that files opened for append cannot be 
truncated, potentially an issue for code that wants to truncate a log 
file for example.

The changes here are along the lines that we discussed. First, the 
opening of files for append is changed back to using GENERIC_WRITE mode. 
Secondly, writing is changed so that it does a write-at-end. This is 
probably the way it should have been done originally. For the 
redirection API, the Windows implementation is changed so that it opens 
the output file in FILE_APPEND_DATA mode. This gives us the semantics 
that we want as we have no control as to how the sub-process will write 
to its output or error streams. One thing to point out is that I have 
deliberately kept the code as simple as possible. That is, I have not 
duplicated the code for long file handling and all the other odd cases 
that Windows entails. The rational is that we could could easily just 
eliminate this and have it use the new file system API to open the file 
(as supporting platform specific options there is easy). However, there 
are modularity concerns with creating that dependency and it might be 
better to see how that plays out first. We can create a low priority bug 
as a reminder of this odd cases. That's mostly it except for some 
additional tests for these scenarios.

The webrev with the changes is here:




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