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diff --git a/open_issues/synchronous_ipc.mdwn b/open_issues/synchronous_ipc.mdwn new file mode 100644 index 00000000..57bcdda7 --- /dev/null +++ b/open_issues/synchronous_ipc.mdwn @@ -0,0 +1,64 @@ +[[!meta copyright="Copyright © 2012 Free Software Foundation, Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag open_issue_hurd]] + + +# IRC, freenode, #hurd, 2012-07-20 + +From [[Genode RPC|microkernel/genode/rpc]]. + + <braunr> assuming synchronous ipc is the way to go (it seems so), there is + still the need for some async ipc (e.g signalling untrusted recipients + without risking blocking on them) + <braunr> 1/ do you agree on that and 2/ how would this low-overhead async + ipc be done ? (and 3/ are there relevant examples ? + <antrik> if you think about this stuff too much you will end up like marcus + and neal ;-) + <braunr> antrik: likely :) + <antrik> the truth is that there are various possible designs all with + their own tradeoffs, and nobody can really tell which one is better + <braunr> the only sensible one i found is qnx :/ + <braunr> but it's still messy + <braunr> they have what they call pulses, with a strictly defined format + <braunr> so it's actually fine because it guarantees low overhead, and can + easily be queued + <braunr> but i'm not sure about the format + <antrik> I must say that Neal's half-sync approach in Viengoos still sounds + most promising to me. it's actually modelled after the needs of a + Hurd-like system; and he thought about it a lot... + <braunr> damn i forgot to reread that + <braunr> stupid me + <antrik> note that you can't come up with a design that allows both a) + delivering reliably and b) never blocking the sender -- unless you cache + in the kernel, which we don't want + <antrik> but I don't think it's really necessary to fulfill both of these + requirements + <antrik> it's up to the receiver to make sure it gets important signals + <braunr> right + <braunr> caching in the kernel is ok as long as the limit allows the + receiver to handle its signals + <antrik> in the Viengoos approach, the receiver can allocate a number of + receive buffers; so it's even possible to do some queuing if desired + <braunr> ah great, limits in the form of resources lent by the receiver + <braunr> one thing i really don't like in mach is the behaviour on full + message queues + <braunr> blocking :/ + <braunr> i bet the libpager deadlock is due to that + +[[libpager_deadlock]]. + + <braunr> it simply means async ipc doesn't prevent at all from deadlocks + <antrik> the sender can set a timeout. blocking only happens when setting + it to infinite... + <braunr> which is commonly the case + <antrik> well, if you see places where blocking is done but failing would + be more appropriate, try changing them I'd say... + <braunr> it's not that easy :/ |