JRuby flock silently converts LOCK_EX to LOCK_SH on read-only files
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Key: JRUBY-5627
URL: http://jira.codehaus.org/browse/JRUBY-5627
Project: JRuby
Issue Type: Bug
Components: Core Classes/Modules
Affects Versions: JRuby 1.6
Environment: Solaris 10
Reporter: Clayton O'Neill
Priority: Minor
In JRUBY-1214 the behavior of File.flock was changed to silently convert
LOCK_EX locks on files opened in read mode into LOCK_SH locks. This was
because some operating systems allow setting LOCK_EX on files opened for read
only. However, this is not specified in
[POSIX|http://pubs.opengroup.org/onlinepubs/009695399/functions/fcntl.html].
In fact, on Solaris, when trying to get an exclusive lock on a file opened only
for read, the OS will return EBADF. So this isn't really a MRI vs JVM issue,
but an OS issue. Any code that depends on this behavior in MRI is not portable.
All of that aside, this violates the principle of least surprise. No one
asking for an exclusive lock is going to be happy when their lock is silently
converted to a shared lock, and this could very easily lead to silent data
corruption.
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