From owner-freebsd-current  Tue Jul  3 22:47:48 2001
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Date: Wed, 4 Jul 2001 01:47:03 -0400
From: David Hill <djhill@novagate.net>
To: freebsd-current@freebsd.org
Subject: system and (v)fork
Message-Id: <20010704014703.4ec62b5f.djhill@novagate.net>
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Hello -

Reading Advanced Programming in the UNIX Environment by Richard W. Stevens, I see that he says that vfork() should be used instead of fork() when you just need to use one of the exec() functions, since it doesn't need to fully copy the address space.

Later in the book, he has an example system() which uses fork() to run /bin/sh -c via the execl() function.

Why wouldn't he use vfork() instead of fork()?

I ran FreeBSD's version of system() both by the default (using fork()) and by using vfork()
I ran a loop 1000 times that called system("echo");

Here are my results:
time ./app

fork()             vfork()
1. 4.528           3.056
   0.050           0.058
   2.078           1.492

2. 3.652           2.865
   0.060           0.060
   2.036           1.484

3. 3.735           3.022
   0.068           0.041
   2.031           1.506

As you can see, vfork() performed better.

But, I am sure there is good reasoning for using fork() over vfork() in the system() call, and I am just curious why.

Can anyone explain this?

Thanks
- David

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