Christoph, > Dmitry, I think you are referring to an outdated version of the > webrev, the current one is this:
Yes. Sorry! You may consider a bit different approach to save memory: Allocate multiple baseTables for different ranges of fd's with plain array of 32 * (fdEntry_t*) for simple case. i.e. if (fd < 32) do plain array lookup if (fd < N1) do two steps lookup in baseTable1 if (fd < N2) do two steps lookup in baseTable2 ... -Dmitry On 2016-03-01 13:47, Langer, Christoph wrote: > Hi Dmitry, Thomas, > > Dmitry, I think you are referring to an outdated version of the > webrev, the current one is this: > http://cr.openjdk.java.net/~stuefe/webrevs/8150460-linux_close-fdTable/webrev.01/webrev/ > > However, I agree - the lock should probably not be taken every time > but only in the case where we find the entry table was not yet > allocated. > > So, maybe getFdEntry should always do this: entryTable = > fdTable[rootArrayIndex]; // no matter if rootArrayIndex is 0 > > Then check if entryTable is NULL and if yes then enter a guarded > section which does the allocation and before that checks if another > thread did it already. > > Also I'm wondering if the entryArrayMask and the rootArrayMask should > be calculated once in the init() function and stored in a static > field? Because right now it is calculated every time getFdEntry() is > called and I don't think this would be optimized by inlining... > > Best regards Christoph > > -----Original Message----- From: core-libs-dev > [mailto:core-libs-dev-boun...@openjdk.java.net] On Behalf Of Dmitry > Samersoff Sent: Dienstag, 1. März 2016 11:20 To: Thomas Stüfe > <thomas.stu...@gmail.com>; Java Core Libs > <core-libs-dev@openjdk.java.net> Subject: Re: RFR(s): 8150460: > (linux|bsd|aix)_close.c: file descriptor table may become large or > may not work at all > > Thomas, > > Sorry for being later. > > I'm not sure we should take a lock at ll. 131 for each fdTable > lookup. > > As soon as we never deallocate fdTable[base_index] it's safe to try > to return value first and then take a slow path (take a lock and > check fdTable[base_index] again) > > -Dmitry > > > On 2016-02-24 20:30, Thomas Stüfe wrote: >> Hi all, >> >> please take a look at this proposed fix. >> >> The bug: https://bugs.openjdk.java.net/browse/JDK-8150460 The >> Webrev: >> http://cr.openjdk.java.net/~stuefe/webrevs/8150460-linux_close-fdTable/webrev.00/webrev/ >> >> >> Basically, the file descriptor table implemented in linux_close.c may not >> work for RLIMIT_NO_FILE=infinite or may grow very large (I saw a >> 50MB table) for high values for RLIMIT_NO_FILE. Please see details >> in the bug description. >> >> The proposed solution is to implement the file descriptor table not >> as plain array, but as a twodimensional sparse array, which grows >> on demand. This keeps the memory footprint small and fixes the >> corner cases described in the bug description. >> >> Please note that the implemented solution is kept simple, at the >> cost of somewhat higher (some kb) memory footprint for low values >> of RLIMIT_NO_FILE. This can be optimized, if we even think it is >> worth the trouble. >> >> Please also note that the proposed implementation now uses a mutex >> lock for every call to getFdEntry() - I do not think this matters, >> as this is all in preparation for an IO system call, which are >> usually way more expensive than a pthread mutex. But again, this >> could be optimized. >> >> This is an implementation proposal for Linux; the same code found >> its way to BSD and AIX. Should you approve of this fix, I will >> modify those files too. >> >> Thank you and Kind Regards, Thomas >> > > -- Dmitry Samersoff Oracle Java development team, Saint Petersburg, Russia * I would love to change the world, but they won't give me the sources.