[Haskell-cafe] Glasgow Distributed Haskell

szefirov at ot.ru szefirov at ot.ru
Sun Jan 28 10:09:33 EST 2007

Paul Johnson пишет:

> Joel Reymont <joelr1 at gmail.com> wrote:
>> I'm after Erlang in Haskell, if you will, for fault-tolerance and 
>> scalability.
> I think the way to do Erlang in Haskell is to build a middleware layer 
> on top of the language, not try to make the language into something it 
> is not. In this kind of environment you need to be able to upgrade 
> components while the system is running. The careful Haskell habit of 
> separating stateful operations from pure functions is useful here. I 
> gather that the HAppS project is working along similar lines, and for 
> similar reasons. Take a look at it.

I think I should point you to:
*Practical Dynamic Software Updating for C*. Iulian Neamtiu, Michael 
Hicks, Gareth Stoyle, and Manuel Oriol. In /Proceedings of the ACM 
Conference on Programming Language Design and Implementation (PLDI)/, 
pages 72-83, June 2006.

Software updates typically require stopping and restarting an 
application, but many systems cannot afford to halt service, or would 
prefer not to. /Dynamic software updating/ (DSU) addresses this 
difficulty by permitting programs to be updated while they run. DSU is 
appealing compared to other approaches for on-line upgrades because it 
is quite general and requires no redundant hardware. The challenge is in 
making DSU /practical/: it should be flexible, and yet safe, efficient, 
and easy to use.

In this paper, we present Ginseng, a DSU implementation for C that aims 
to meet this challenge. We compile programs specially so that they can 
be dynamically patched, and generate most of a dynamic patch 
automatically. Ginseng performs a series of analyses that when combined 
with some simple runtime support ensure that an update will not violate 
type-safety while guaranteeing that data is kept up-to-date. We have 
used Ginseng to construct and dynamically apply patches to three 
substantial open-source server programs-/Very Secure FTP daemon/, 
/OpenSSH sshd daemon/, and /GNU Zebra/. In total, we dynamically patched 
each program with three years' worth of releases. Though the programs 
changed substantially, the majority of updates were easy to generate. 
Performance experiments show that all patches could be applied in less 
than 5 /ms/, and that the overhead on application throughput due to 
updating support ranged from 0 to at most 32%.

So, it is not completely impossible for haskell being updated on-the-fly.

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