[PATCH][analyzer] Prevent ccc/c++-analyzer from hanging on Windows.

[Anton Yartsev]

On 06.11.2014 20:27, Jordan Rose wrote:
> I think my point was "why bother forking at all if we're using open to 
> run a subprocess?".
Ah, got it! Attached is an updated patch.

>
> Also, this will fail if the path contains spaces:
Corrected.

>
> +    my $ExecLine = join(' ', $Clang, "-###", $mode, @$Args, "2>&1", "|");
> +    open(PS, $ExecLine);
>
> Do newer Perls on newer Windows support the list form of open?
No, at least ActivePerl, StrawberryPerl and Dwimperl.

Current perl docs state:
'open to ||-| and |-|| are unsupported. (Win32, RISC OS)' 
(http://perldoc.perl.org/perlport.html#open)
and
'The open(FOO, "|-") and open(BAR, "-|") constructs are not yet 
implemented.' (http://perldoc.perl.org/perlfork.html)

> Jordan
>
>
>> On Nov 5, 2014, at 11:54 , Anton Yartsev <anton.yartsev at gmail.com 
>> <mailto:anton.yartsev at gmail.com>> wrote:
>>
>> Ping!
>>> It seems that fork is the only native perl mean for creating 
>>> subprocesses. There is a number of packages that provide means for 
>>> spawning at cpan.org <http://cpan.org>, but they are not guarantee 
>>> to be included at the users perl distribution.
>>>> Looking at this code, it's weird that we're doing this as a 
>>>> fork/exec (or not-exec) at all. Why can't we just spawn a sub-process?
>>>>
>>>> Jordan
>>>>
>>>>
>>>> On Oct 21, 2014, at 6:47 , Anton Yartsev <anton.yartsev at gmail.com 
>>>> <mailto:anton.yartsev at gmail.com>> wrote:
>>>>
>>>>> Hi all,
>>>>>
>>>>> Attached is the patch that prevents ccc/c++-analyzer from hang if 
>>>>> launched with ActivePerl or Strawberry Perl interpreters.
>>>>> The patch replaces the code that creates a pipe from child to 
>>>>> parent to the more portable explicit writing to parent, this 
>>>>> prevent interpreters from hang.
>>>>> The conditions for hang are: child should open a pipe to the 
>>>>> parent and parent should read from the child, otherwise no hang.
>>>>>
>>>>> The problem is possibly caused by the bug in emulation of 'fork' 
>>>>> by Perl interpreters on Windows. From perlfork 
>>>>> <http://perldoc.perl.org/perlfork.html> documentation, BUGS section:
>>>>> "In certain cases, the OS-level handles created by the pipe(), 
>>>>> socket(), and accept() operators are apparently not duplicated 
>>>>> accurately in pseudo-processes. This only happens in some 
>>>>> situations, but where it does happen, it may result in deadlocks 
>>>>> between the read and write ends of pipe handles, or inability to 
>>>>> send or receive data across socket handles."
>>>>>
>>>>> An example from perlfork documentation also hangs:
>>>>>
>>>>> # simulate open(FOO, "-|")
>>>>> sub pipe_from_fork ($) {
>>>>>     my $parent = shift;
>>>>>     pipe $parent, my $child or die;
>>>>>     my $pid = fork();
>>>>>     die "fork() failed: $!" unless defined $pid;
>>>>>     if ($pid) {
>>>>>       close $child;
>>>>>     }
>>>>>     else {
>>>>>       close $parent;
>>>>>       open(STDOUT, ">&=" . fileno($child)) or die;
>>>>>     }
>>>>>   $pid;
>>>>> }
>>>>>
>>>>> if (pipe_from_fork('BAR')) {
>>>>> # parent
>>>>> while (<BAR>) { print; }
>>>>>   close BAR;
>>>>> }
>>>>> else {
>>>>>   # child
>>>>>   print "pipe_from_fork\n";
>>>>>   exit(0);
>>>>> }
>>>>>
>>>>> The hang is not reproduced only with the MSYS Perl.
>>>>>
>>>>> OK to commit?
>>>>> -- 
>>>>> Anton
>>>>> <ccc-analyzer_fork_open_hang.patch>
>>>>
>>>
>>>
>>> -- 
>>> Anton
>>
>>
>> -- 
>> Anton
>


-- 
Anton

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20141111/dde821ce/attachment.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: ccc-analyzer_fork_open_hang_v2.patch
Type: text/x-diff
Size: 2022 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20141111/dde821ce/attachment.patch>