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
