Re: RFR 9: 8078099 : (process) ProcessHandle should uniquely identify processes

[Roger Riggs]

Hi Volker,

Sure, let me know what is different about AIX and how it should/can be 
fixed.

Thanks, Roger


On 7/7/2015 3:29 AM, Volker Simonis wrote:
Hi Roger,

sorry but I only now noticed this RFR. Can you please temporary hold
this change back. I think it needs some adjustments on AIX. I'll look
into it today and let you know.

Thanks,
Volker



On Mon, Jul 6, 2015 at 4:47 PM, Roger Riggs <roger.ri...@oracle.com> wrote:
Hi Peter,

Thanks for reviewing the new implementation.

The idea to pre-allocate the buffer based on the size of the output arrays
passed for output
will not work as desired.
The same native code entry point is used whether it is a query for all
processes or
just the immediate children.  In either case, the buffer for sysctl needs to
be
large enough to accommodate all of the OS threads; its not a function of the
output array size.

With respect to the buffer allocation on OS X, I might see the point of a
retry
when sysctl returns ENOMEM;


I don't think its particularly worthwhile to add the native code to retry in
the case
of ENOMEM. The OSX doc for sysctrl does indicate it tries to round up
to avoid a subsequent failure.
The ProcessHandle API already cautions that the list of processes is dynamic
and that processes may started or terminate concurrently with the call  to
children/allChildren.
So if the sysctl returns ENOMEM indicating not all the processes fit; the
ones
that do fit within in the allocated buffer are valid at that point in time.
If there are extras that do not fit in the buffer they are likely to be
'newer'
processes and can be considered to have been started 'after' the
children/allChildren invocation.
So I propose to change the error checking to consider ENOMEM as a
non-exceptional
return and return the processes available.

Thanks, Roger




On 7/2/2015 3:32 AM, Peter Levart wrote:
Hi Roger,

I looked at the code briefly and have the following comments:

For ProcessHandleImpl_macosx.c, in method getProcessPids0:

  224     // Get buffer size needed to read all processes
  225     int mib[4] = {CTL_KERN, KERN_PROC, KERN_PROC_ALL, 0};
  226     if (sysctl(mib, 4, NULL, &bufSize, NULL, 0) < 0) {
  227         JNU_ThrowByNameWithLastError(env,
  228             "java/lang/RuntimeException", "sysctl failed");
  229         return -1;
  230     }
  231
  232     // Allocate buffer big enough for all processes
  233     void *buffer = malloc(bufSize);
  234     if (buffer == NULL) {
  235         JNU_ThrowOutOfMemoryError(env, "malloc failed");
  236         return -1;
  237     }
  238
  239     // Read process info for all processes
  240     if (sysctl(mib, 4, buffer, &bufSize, NULL, 0) < 0) {
  241         JNU_ThrowByNameWithLastError(env,
  242             "java/lang/RuntimeException", "sysctl failed");
  243         free(buffer);
  244         return -1;
  245     }

... the 1st call to sysctl is used to measure the size of the needed
buffer and the 2nd call fills-in the buffer. The documentation for sysctl
says:

"     The information is copied into the buffer specified by oldp. The
size of the buffer is given by the
      location specified by oldlenp before the call, and that location
gives the amount of data copied after
      a successful call and after a call that returns with the error code
ENOMEM.  If the amount of data
      available is greater than the size of the buffer supplied, the call
supplies as much data as fits in
      the buffer provided and returns with the error code ENOMEM. If the
old value is not desired, oldp and
      oldlenp should be set to NULL.

      The size of the available data can be determined by calling sysctl()
with the NULL argument for oldp.
      The size of the available data will be returned in the location
pointed to by oldlenp.  For some opera-tions, operations,
      tions, the amount of space may change often.  For these operations,
the system attempts to round up so
      that the returned size is large enough for a call to return the data
shortly thereafter."

So while not very probable, it can happen that you get ENOMEM from 2nd
call because of underestimated buffer size. Would it be better to retry
(re)allocation of buffer and 2nd call in a loop with new estimation returned
from previous call while the error is ENOMEM?

Another suggestion: What would it be if the buffer size estimation was not
computed by a call to sysctl with NULL buffer, but was taken from the
passed-in resulting array size(s). In case the user passes-in arrays of
sufficient size, you can avoid double invocation of sysctl. Also, if ENOMEM
happens, you can just return the result obtained and the new estimation - no
looping in native code. The UNIX, Solaris and Windows variants look good.

Regards, Peter

On 06/22/2015 05:10 PM, Roger Riggs wrote:
Please review changes to ProcessHandle implementation to uniquely
identify
processes based on the start time provided by the OS. It addresses the
issue
of PID reuse.

This is the implementation of the ProcessHandle.equals() spec change in
     8129344 : (process) ProcessHandle instances should define equals and
be value-based

Webrev:
http://cr.openjdk.java.net/~rriggs/webrev-starttime-8078099/

Issue:
https://bugs.openjdk.java.net/browse/JDK-8078099

Thanks, Roger