From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <69de78bb2dcc84f725ceea4b529c1ec4@9fs.org>
To: 9fans@cse.psu.edu
Subject: Re: [9fans] how to avoid a memset() optimization
From: nigel@9fs.org
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Date: Mon,  6 Jan 2003 10:47:07 +0000
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Or

        failed = 1;
        if ((res1 = lock(A) != 0)
	        if ((res2 = lock(B) != 0) {
		        if ((res3 = lock(C) != 0) {
				foo(res1, res2, res3);
				failed = 0;
			}
	if (res3 != 0)
        		release(C);
	if (res2 != 0)
        		release(B);
	if (res1 != 0)
        		release(A);

        return failed;

avoiding the goto.

Further, if release(nil) is implemented as a noop you can have

        failed = 1;
        if ((res1 = lock(A) != 0)
	        if ((res2 = lock(B) != 0) {
		        if ((res3 = lock(C) != 0) {
				foo(res1, res2, res3);
				failed = 0;
			}
	release(C);
	release(B);
	release(A);

        return failed;

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To: 9fans@cse.psu.edu
From: Ralph Corderoy <ralph@inputplus.co.uk>
Message-ID: <3afa.3e16dd11.67d1a@blake.inputplus.co.uk>
Organization: InputPlus Ltd.
References: <38aa463bafe23035decff6b0364f7553@plan9.bell-labs.com>, <20021119103808.B13548@unicorn.math.spbu.ru>
Subject: Re: [9fans] how to avoid a memset() optimization
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Date: Mon, 6 Jan 2003 10:18:19 GMT

Hi Roman,

> Of course, good old:
>      
>      if ((a = do_it()) == BadThingHappened)
>           return TellEmAboutIt;
> 
> works, but costs a little bit too much when clarity is needed.
> Especially when a "transaction" like pattern is needed ( e.g. I need
> to to have o1 = f1(); o2 = f2(); o3 = f3(); but if any of f* fails, I
> have to destroy what I've got so far ). 

A common way of doing this is using goto.

        failed = 1;

        if ((res1 = lock(A) == 0) {
            goto releaseA;
        }
        if ((res2 = lock(B) == 0) {
            goto releaseB;
        }
        if ((res3 = lock(C) == 0) {
            goto releaseC;
        }

        foo(res1, res2, res3);
        failed = 0;

    releaseC:
        release(C);
    releaseB:
        release(B);
    releaseA:
        release(A);

        return failed;

Cheers,

-- 
Ralph Corderoy.      http://inputplus.co.uk/ralph/     http://troff.org/
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