Hi Carlos, On 07/12/2017 06:57 PM, Carlos O'Donell wrote: > Since glibc 2.25 the PID cache is removed. Allelujah! Patch applied. Thanks! Cheers, Michael > Rationale given in the release notes: > https://sourceware.org/glibc/wiki/Release/2.25#pid_cache_removal > ~~~ > 3.2.3. Calls to getpid are no longer cached > > The PID cache used by glibc has been removed. In certain scenarios > the cache was not 100% reliable and because of that it was deemed > safer to remove the cache than to potentially return a wrong answer. > > Applications performing getpid() calls in a loop will see the worst > case performance degradation as the library call will perform a > system call at each invocation. Such application uses were known > to exist at least in OpenSSL (fork()-based PRNG invalidation), > but supporting the performance of that specific invalidation > mechanism was not judged to have sufficient value against > immediate and long-term benefits of removing the cache. > > Functional reasons exist for the PID cache removal including > problems with PID namespaces, interoperability with raw system > calls (BZ#17214, Chrome: Issue 800183004), and improvements to > spawn (BZ#19957). Performance is actually increased in > pthread_create() with the removal of the cache since the > implementation no longer needs to perform an invalidation step. > > Applications performing getpid() in a loop that need to do > some level of fork()-based invalidation can instead use > pthread_atfork() to register handlers to handle the invalidation. > There is work-in-progress to make pthread_atfork() available > to applications that do not link against libpthread.so > (Provide pthread_atfork() without libpthread.so). > > Other kinds of invalidation are not supported and the glibc > community will actively look at a kernel assisted mechanism > for state management across fork(), vfork(), clone() and other > interfaces which can benefit from such semantics. It is the > same type of solution required for crypto PRNG reset across > such API calls. > ~~~ > > Signed-off-by: Carlos O'Donell <carlos@xxxxxxxxxx> > > diff --git a/man2/getpid.2 b/man2/getpid.2 > index 1927607..45d71a6 100644 > --- a/man2/getpid.2 > +++ b/man2/getpid.2 > @@ -112,6 +112,11 @@ for discussion of a case where > may return the wrong value even when invoking > .BR clone (2) > via the glibc wrapper function. > + > +Since glibc version 2.25, the PID cache is removed, and calls to > +.BR getpid () > +will not be cached. > + > .SH SEE ALSO > .BR clone (2), > .BR fork (2), > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
