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Add a comment, and two BOOST_ASSERTs to detect the possible infinite loop described in ticket 4438 in case my analysis that the infinite loop will never happen is wrong.

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Beman
2014-12-26 10:07:43 -05:00
parent fb824af6e3
commit 704f4e328d
1 changed files with 13 additions and 5 deletions
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18
src/operations.cpp
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@@ -444,25 +444,33 @@ namespace
ssize_t sz, sz_read=1, sz_write;
while (sz_read > 0
&& (sz_read = ::read(infile, buf.get(), buf_sz))> 0)
&& (sz_read = ::read(infile, buf.get(), buf_sz)) > 0)
{
// Allow for partial writes - see Advanced Unix Programming (2nd Ed.),
// Marc Rochkind, Addison-Wesley, 2004, page 94
sz_write = 0;
do
{
BOOST_ASSERT(sz_read - sz_write > 0); // #1
// ticket 4438 claimed possible infinite loop if write returns 0. My analysis
// is that POSIX specifies 0 return only if 3rd arg is 0, and that will never
// happen due to loop entry and coninuation conditions. BOOST_ASSERT #1 above
// and #2 below added to verify that analysis.
if ((sz = ::write(outfile, buf.get() + sz_write,
sz_read - sz_write))< 0)
sz_read - sz_write)) < 0)
{
sz_read = sz; // cause read loop termination
break; // and error to be thrown after closes
break; // and error reported after closes
}
BOOST_ASSERT(sz > 0); // #2
sz_write += sz;
} while (sz_write < sz_read);
}
if (::close(infile)< 0)sz_read = -1;
if (::close(outfile)< 0)sz_read = -1;
if (::close(infile)< 0)
sz_read = -1;
if (::close(outfile)< 0)
sz_read = -1;
return sz_read >= 0;
}