6348631 - request for review

[Ivan Krylov]

On 19.11.2010 13:33, Volker Simonis wrote:
> What about the O_DELTE stuff? Is it really necessary. Additionally to
> my comments, it is also not available in the Windows version of
> os::open()!

I am leaving this functionality unchanged with respect to the original code on all operating systems.

Ivan

> And please try to keep merges at a minimum - especially with regard to
> the other BIG changes which are in the queue (includeDB, Symtable).
> Please see my comments and the discussion about this topic in the
> review for 6990754:
>
> http://old.nabble.com/Request-for-review-%28XL%29-6990754%3A-Use-native-memory-and-reference-counting-to-implement-SymbolTable-tt30138063.html#a30138063
>
>
> On Fri, Nov 19, 2010 at 11:19 AM, Ivan Krylov<Ivan.Krylov at oracle.com>  wrote:
>> David, Volker,
>>
>> Thanks for your feedbacks. My comments are inlined.
>> Here is a new webrev with suggested changes
>> http://cr.openjdk.java.net/~ikrylov/6348631.v2/
>>
>> Thanks,
>>
>> Ivan
>>
>> On 19.11.2010 3:41, David Holmes wrote:
>>> Hi Volker,
>>>
>>> Just exploring a couple of your comments further ...
>>>
>>> Volker Simonis said the following on 11/19/10 04:18:
>>>> os.hpp
>>>> ======
>>>>
>>>> - I would suggest to rename:
>>>>
>>>> static size_t hpi_read(int fd, void *buf, unsigned int nBytes);
>>>>
>>>> into:
>>>>
>>>> static size_t restartable_read(int fd, void *buf, unsigned int nBytes);
>>>>
>>>> because this is exactly what it does in contrast to the vanilla 'read()'
>>>> function. After all this change wants to get rid of HPI, so there's no
>>>> reason
>>>> why to still keep this acronym floating around:)
>>> On Linux os::read and os::hpi_read differ by the latter being restartable,
>>> but on Solaris they are both "restartable" and both interruptible - but
>>> differ in their expectations/requirements as to the state of the thread when
>>> called. In that regard keeping the old hpi_read name reflects the fact that
>>> this function replaces hpi::read and is only used for that case - whereas
>>> using restartable_read would not correctly distinguish the two use cases.
>> Note that restartable behavior for Solaris will fade away. It will be
>> non-default for jdk7 and presumably unsupported for jdk8.
>>
>>>> line 410ff
>>>> ----------
>>>>
>>>> - I don't really understand the comment:
>>>>
>>>> // os::read for calls from non native state
>>>> // For performance, os::read is only callable from _thread_in_native
>>>>
>>>> and this is apparently only applicable to the Solaris version of
>>>> 'os::read()'. As far as I understand this is need for 'interruptible' IO
>>>> which
>>>> is the default on Linux but requires special handling on Solaris. Make
>>>> this
>>>> more explicit in the comment and explain the difference to the
>>>> 'restartable_read()' version below.
>>> Interruptible I/O is only supported on Solaris, not Linux**. On Linux
>>> os::read is simply ::read. The issue here is the state of the thread when it
>>> calls the function. I agree that Solaris details should not be evident in
>>> the os.hpp header.
>> So I guess it is best to remove this comment from os.hpp as a
>> platform-dependent statement.
>>
>>> ** There are two sides to "interruptible I/O":
>>>
>>> 1. How does the syscall respond to a signal delivery
>>> 2. Does Thread.interrupt cause a signal to be generated
>>>
>>> I think #1 is configurable when you install the signal handler. But #2 is
>>> only done on Solaris (see os::interrupt).
>>>
>>>> os_linux.cpp
>>>> ============
>>>>
>>>> _print_ascii_file()
>>>> -------------------
>>>> you replace:
>>>>   open() ->  ::open()
>>>>   close() ->  ::close()
>>>>
>>>> BUT
>>>>
>>>>   read() ->  os::read()
>>>>
>>>> Why do you change the behavior for open() while leaving open() and
>>>> close()
>>>> unchanged? Notice that _print_ascii_file() called the global 'read()'
>>>> function
>>>> before, because it is not a class method of the 'os' class!
>>> I agree. For Linux this change makes no difference as os::read == ::read,
>>> but then the change also makes no sense as even Solaris still calls ::read.
>> Good catch. I did not want to change and behavior, calls to libc should
>> remain calls to libc,
>>
>>> I'd even suggest _print_ascii file could be moved into os.cpp as a
>>> private/static member of os (there's way too much duplication in the
>>> os_<os>.cpp files)
>> I would like to leave code refactoring outside of scope of this fix. There
>> are many more places where code refactoring would be needed. Perhaps after
>> the coming changes in the build system it will be much easier to perform
>> this work.
>>
>>>> jvm.cpp
>>>> =======
>>>> JVM_LEAF(jint, JVM_Read(jint fd, char *buf, jint nbytes))
>>>>   JVMWrapper2("JVM_Read (0x%x)", fd);
>>>>
>>>>   //%note jvm_r6
>>>>   // not doing restartable read to avoid performance hit
>>>>   return (jint)os::hpi_read(fd, buf, nbytes);
>>>> JVM_END
>>>>
>>>> - the new comment 'not doing restartable read to avoid performance hit'
>>>> is
>>>>   misleading here, because on Linux 'os::hpi_read()' is restartable.
>>>> That's
>>>>   exactly the difference between 'read()' and 'hpi_read()' and that's why
>>>> I
>>>>   suggested to rename 'hpi_read()' to 'restartable_read()'
>>> As per the above that's only true on Linux. But I agree that the comment
>>> is wrong. It is also very unclear why hpi_read needs to be called in this
>>> case. Again I suspect it is the state of the thread that affects what
>>> happens on Solaris.
>> I agree that th comment is not reflecting the code below and therefore
>> removing it. I thing at some point I wanted to do os:read there but later
>> encountered problems with it.
>> There was another earlier proposal to do libc read in the class loader but I
>> seem to get problems with that as well therefore removed from this fix.
>>
>>> Cheers,
>>> David
>>> -----
>>>
>>>
>>>> On Thu, Nov 18, 2010 at 8:07 AM, Ivan Krylov<Ivan.Krylov at oracle.com>
>>>> wrote:
>>>>> With this fix we are removing the use of the HPI (Host Portable
>>>>> interface)
>>>>> library from jvm.
>>>>>
>>>>> Webrev: http://cr.openjdk.java.net/~ikrylov/6348631/
>>>>>
>>>>>
>>>>>