From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: fac41,9a0ff0bffdf63657 X-Google-Attributes: gidfac41,public X-Google-Thread: 1108a1,9a0ff0bffdf63657 X-Google-Attributes: gid1108a1,public X-Google-Thread: f43e6,9a0ff0bffdf63657 X-Google-Attributes: gidf43e6,public X-Google-Thread: 103376,4b06f8f15f01a568 X-Google-Attributes: gid103376,public From: "Robert Martin" Subject: Re: Software landmines (loops) Date: 1998/09/02 Message-ID: <6sjl6v$5qh$1@hirame.wwa.com>#1/1 X-Deja-AN: 387141520 References: <6renh8$ga7$1@nnrp1.dejanews.com> <6rf59b$2ud$1@nnrp1.dejanews.com> <6rfra4$rul$1@nnrp1.dejanews.com> <35DBDD24.D003404D@calfp.co.uk> <6sbuod$fra$1@hirame.wwa.com> <35f51e53.48044143@news.erols.com> <6sdiav$e0g$1@hirame.wwa.com> <6sfcft$70p$1@hirame.wwa.com> <6shp40$ec8$1@nnrp1.dejanews.com> <6sie46$eb7$1@hirame.wwa.com> <6siijm$h1m$1@hirame.wwa.com> X-MimeOLE: Produced By Microsoft MimeOLE V4.72.2106.4 Organization: WorldWide Access - Midwestern Internet Services - www.wwa.com Newsgroups: comp.lang.eiffel,comp.object,comp.software-eng,comp.lang.ada Date: 1998-09-02T00:00:00+00:00 List-Id: Matthew Heaney wrote in message ... >"Robert Martin" writes: > >> Of course later on, someone asks us to sieze and release a mutex for each >> iteration of the loop. We'd like to put the seize as the first line of the >> loop body, and the release as the last line of the loop body. But if there >> are early exits, then we must put a release before every exit. > >No. Use a controlled type (construction/deconstruction) to >automatically seize and release: > >loop > declare > Lock : Mutex_Lock (Mutex'Access); > begin > > end; >end loop; > > >When you enter the loop, the Lock object elaborates, and during its >initialization, it automatically calls the Seize operation of Mutex. > >When you leave the loop - via a return, or an exit, or an exception, or >whatever - the Lock object is Finalized, during which time it >automatically calls the Release operation of Mutex. > >So no, you don't have to worry about bailing out early. There is no >maintenance penalty for an early return from the loop. This is true if: 1. Your language has controlled types. 2. The cleanup that needs to be done can be done from the finalizer. For example, in C++ the equivalent scheme is to use a destructor. However the destructor is in a completely different scope. So extraordinary means may need to be used to allow the destructor access to the variables that need finalization. Consider the case of a complex data structure. You are in the midst of changing a set of variables within it. Suddenly you realize that you must exit early. Before you can exit, you have to put the data structure back the way it was. In C++, getting a destructor to do this can be horrific. The point is that controlled types are not a generally applicable solution, since not all languages have them, and not all languages implement them well. BTW, in essense a controlled type is simply a way to enforce that a scope has a single exit. By using single-entry/single-exit style, *all* your variables are controlled -- albeit manually. (excluding exceptions). Robert C. Martin | Design Consulting | Training courses offered: Object Mentor | rmartin@oma.com | Object Oriented Design 14619 N Somerset Cr | Tel: (800) 338-6716 | C++ Green Oaks IL 60048 | Fax: (847) 918-1023 | http://www.oma.com "One of the great commandments of science is: 'Mistrust arguments from authority.'" -- Carl Sagan