From owner-freebsd-current@freebsd.org Fri Oct 6 03:39:38 2017 Return-Path: Delivered-To: freebsd-current@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A6686E259CD for ; Fri, 6 Oct 2017 03:39:38 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: from mail-io0-x232.google.com (mail-io0-x232.google.com [IPv6:2607:f8b0:4001:c06::232]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 6294D6CB90 for ; Fri, 6 Oct 2017 03:39:38 +0000 (UTC) (envelope-from wlosh@bsdimp.com) Received: by mail-io0-x232.google.com with SMTP id f72so8619366ioj.5 for ; Thu, 05 Oct 2017 20:39:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bsdimp-com.20150623.gappssmtp.com; s=20150623; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=xr9slmh/JWuj8bqDgkhJnBHrTiTPeMTR4myEPJV5i3g=; b=FOJvpGmMDZGwzpaHUpRvgzLAX+mNxix5ckFjLJuqwAk164FcqP0IQEg2UwvTxErGDS OE8evf/7yjxobmuxFmM2xz7HFGnxEoZ9bfgopNflt0wx8SR+TAHnh3x0cu6rdYS1P0X3 aRdO79ttZllCUmLaP2c1HhfOVIUaf//Xx7DjPyu+V60tg0sQBfN1HwFusGXwVQsK/plF mLszzAWXH4cqwHilGnz8N0xKNTs2MWAOwBX9nEA/UdUxUxUVxA1r/yhKsxvClqP1gidz K8cP4EBRxFmOt3f9a4tClzA56bfeT55mEJmq00gxyhJikVX2ik6uMUrFHr8Ws4vA+QkE INcw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=xr9slmh/JWuj8bqDgkhJnBHrTiTPeMTR4myEPJV5i3g=; b=nXVxdhgd+PQbgCBxzzUzVK3eq5TXX4xyDeEbGUQGkFp4veLvAl+dp+EOA37OTq/Yy5 YlyfFk7PpHBHbG8Kv3ggHql4qtm6EZne7HauqWT3vbLKNcPt9BPNNQVDUVRfxGCZ8yRz pM1siy1YwpzrtuURSjSIhhviatwn2D5seavKqb5KiqWq75DWnFmlEQUqSZDnsZdmP3nW lEfSeVmWBUD7XDIgu1IDbeJT2UM+9J2SCXiEhDscmLC0Pj7JXXkqjtiBNLQikqGfzQBq zGHizDWEBqVJXhaQ2Wo9dDr5IXcijLRzyMVa7waiz9D4nKk7uvjSuxgqcgerQ2F4VUi9 Bo6g== X-Gm-Message-State: AMCzsaXJEFTLbb1jDtgTmH3gbzk09PNnTIuoHKdXMY0LHNAMtZBGQKCN wQc0xlUkGV3j6VglwzocjdSJzi3M8Y5FfF2TbXRfiw== X-Google-Smtp-Source: AOwi7QCv4BFmPPeE7CZw92llf0tBV+Jqu1jOMeYk/l6ZjcuQcUYdZQuDk+ouR/4mTpk73US8rh3TKBXHxzTGKzvX7OI= X-Received: by 10.107.68.6 with SMTP id r6mr929548ioa.282.1507261177642; Thu, 05 Oct 2017 20:39:37 -0700 (PDT) MIME-Version: 1.0 Sender: wlosh@bsdimp.com Received: by 10.79.94.130 with HTTP; Thu, 5 Oct 2017 20:39:37 -0700 (PDT) X-Originating-IP: [208.185.168.99] In-Reply-To: References: <1507238672.86205.250.camel@freebsd.org> From: Warner Losh Date: Thu, 5 Oct 2017 20:39:37 -0700 X-Google-Sender-Auth: Hy_4DYVzA4Ynk6k5ghiKX4MRcAw Message-ID: Subject: Re: C++ in jemalloc To: David Goldblatt Cc: Ian Lepore , FreeBSD Current Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 06 Oct 2017 03:39:38 -0000 I'm guessing a realistic timeline for us would be on the order of 3 to 6 months. We've been dithering on this issue for a while, and your request seems as good a time as any to get people off the fence... So, if you are targeting FreeBSD 12, then in that time frame, there'd be no issues with C++11 in the form you characterized. FreeBSD 11.x couldn't handle requiring a c++11 compiler to build though, and we're planning another release of that soon. Warner On Thu, Oct 5, 2017 at 4:50 PM, David Goldblatt wrote: > We can avoid it in the short term without a ton of pain. In the long run > it would be nice to have, but I wouldn't want to tie our release schedule > to FreeBSD's too tightly (our CI is improving to the point where the tip of > the dev branch gets tested about as well as releases would be, so we're > trying to de-emphasize release vs. non-release versions). Do you have a > sense of when the situation might change (if only so I know when to check > back)? > > Thanks for the replies on this, they've been super helpful. > > - David > > > On Thu, Oct 5, 2017 at 4:13 PM, Warner Losh wrote: > >> Today C++11 is a no-go generally due to the lagging architectures needing >> gcc 4.2. >> >> However, that answer might change soon. Would it be easy for you to avoid >> C++11, or would that cause you significant pain? And what's the timeline >> you'd be releasing a new jemalloc requiring this stuff? The answers might >> change the 'no-go' to 'ok'. >> >> Warner >> >> >> On Thu, Oct 5, 2017 at 3:00 PM, David Goldblatt < >> davidtgoldblatt@gmail.com> wrote: >> >>> So it sounds like C++03 (or rather, the version of C++ supported by g++ >>> 4.2) will be fine. >>> >>> > Is C++11 a no-go, without breaking libc on non-Clang architectures? (It >>> isn't clear to me if having to use the ports gcc to build was unfortunate >>> or unacceptable from FreeBSD's POV). C++11 would be sort of helpful in the >>> core implementation (we currently have to maintain our own backport of C11 >>> atomics, for instance), but would be really helpful in the test suite >>> (because of how much syntactically simpler it is to, say, spin up a bunch >>> of threads to hammer a local instance of a data structure). >>> >>> - David >>> >>> On Thu, Oct 5, 2017 at 2:33 PM, Warner Losh wrote: >>> >>>> >>>> >>>> On Thu, Oct 5, 2017 at 2:24 PM, Ian Lepore wrote: >>>> >>>>> On Thu, 2017-10-05 at 14:01 -0700, Warner Losh wrote: >>>>> > On Thu, Oct 5, 2017 at 11:59 AM, David Goldblatt >>>>> > wrote: >>>>> > >>>>> > > >>>>> > > Hi all, >>>>> > > >>>>> > > The jemalloc developers have wanted to start using C++ for a >>>>> while, to >>>>> > > enable some targeted refactorings of code we have trouble >>>>> maintaining due >>>>> > > to brittleness or complexity (e.g. moving thousand line macro >>>>> definitions >>>>> > > to templates, changing the build->extract symbols->rebuild >>>>> mangling scheme >>>>> > > for internal symbols to one using C++ namespaces). We'd been >>>>> holding off >>>>> > > because we thought that FreeBSD base all had to compile on GCC >>>>> 4.2, in >>>>> > > order to support some esoteric architectures[1]. >>>>> > > >>>>> > > The other day though, I noticed that there is some C++ shipping >>>>> with >>>>> > > FreeBSD; /usr/bin/dtc and /sbin/devd (the former claiming in the >>>>> HACKING >>>>> > > document that C++11 is a minimum for FreeBSD 11). This, combined >>>>> with the >>>>> > > fact that ports now points to a modern gcc, makes me think we were >>>>> > > incorrect, and can turn on C++ without breaking FreeBSD builds. >>>>> > > >>>>> > > Am I right? Will anything break if jemalloc needs a C++ compiler >>>>> to build? >>>>> > > We will of course not use exceptions, RTTI, global constructors, >>>>> the C++ >>>>> > > stdlib, or anything else that might affect C source or link >>>>> compatibility. >>>>> > > >>>>> > > Thanks, >>>>> > > David (on behalf of the jemalloc developers >>>>> > > >>>>> > > [1] That being said, we don't compile or test on those >>>>> architectures, and >>>>> > > so probably don't work there in the first place if I'm being >>>>> honest. But >>>>> > > we'd also like to avoid making that a permanent state of affairs >>>>> that can't >>>>> > > be changed. >>>>> > > >>>>> > For FreeBSD 10 and earlier, this would likely break all >>>>> architectures that >>>>> > aren't x86. Starting in FreeBSD 11, arm and powerpc are supported by >>>>> clang, >>>>> > but not super well. For FreeBSD 12, we're getting close for >>>>> everything >>>>> > except sparc64 (whose fate has not yet been finally decided). >>>>> > >>>>> > So for the popular architectures, this arrangement might work. For >>>>> building >>>>> > with external toolchains, it might also work. Some of the less >>>>> popular >>>>> > architectures may be a problem. >>>>> > >>>>> > Does that help? It isn't completely cut and dried, but it should be >>>>> helpful >>>>> > for you making a decision. >>>>> > >>>>> > Warner >>>>> >>>>> Wait a sec... we've been compiling C++ code with gcc 4.2 since like >>>>> 2006. What am I missing here that keeps this answer from being a >>>>> simple "go for it"? >>>>> >>>>> Just stay away from C++11 features and gcc 4.2 should work fine. (DTC >>>>> may require C++11, but that was likely the author's choice given that >>>>> there was no requirement for it to work on pre-clang versions of >>>>> freebsd). >>>>> >>>> >>>> It's the ubiquity of C++11 is why I didn't just say "Go for it". >>>> >>>> Warner >>>> >>> >>> >> >