Runtime.exec : vfork() concerns and a fix proposal

[Roger Riggs]

Hi David,

How does your proposal differ from the current posix_spawn and 
jspawnhelper MODE_POSIX_SPAWN
implementation available on Solaris and AIX?
This area is sensitive enough that it would be prudent to implement it 
as a new mode in ProcessImpl/ProcessImpl; retaining the existing options.
Changing the default could be a build option and would require extensive 
testing and a long stability period.

Regards, Roger

On 9/12/18 10:33 AM, David Lloyd wrote:
> On Wed, Sep 12, 2018 at 9:21 AM Martin Buchholz <martinrb at google.com> wrote:
>> I agree that your proposal makes the implementation more robust, so if
>> you are willing to implement it and it doesn't cost too much, then I
>> would support it.  The current implementation doesn't seem to cause
>> trouble in practice, or at least we don't see any bug reports.
>>
>> When you benchmark with open file descriptors, try with and without
>> FD_CLOEXEC flag set.  Almost all fds should be created with the
>> FD_CLOEXEC flag set - openjdk is moving in that direction.  When there
>> are many open files, your implementation may be a weird sort of
>> optimization.
>>
>> On Tue, Sep 11, 2018 at 10:51 AM, Thomas Stüfe <thomas.stuefe at gmail.com> wrote:
>>
>>> The point of this technique is that we minimize the window in the
>>> child between vfork and the first exec. In fact, we are now fully
>>> POSIX compliant.
>> 2004-POSIX compliant ... but in the mean time they removed vfork().
>> But vfork is critical for Google (and probably others)  due to the
>> momentary overcommit problem on Linux.  Or has that changed somehow?
> If the lack of POSIX support is a problem, posix_spawn could possibly
> be used instead in this case:
>
>> The child process is created using vfork(2) instead of fork(2) when [...] file_actions is NULL and the spawn-flags element of the attributes object pointed to by attrp does not contain POSIX_SPAWN_SETSIGMASK, POSIX_SPAWN_SETSIGDEF, POSIX_SPAWN_SETSCHEDPARAM, POSIX_SPAWN_SETSCHEDULER, POSIX_SPAWN_SETPGROUP, or POSIX_SPAWN_RESETIDS.
> This would only work if the helper program is run directly though.
>