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Small fixes.

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[SVN r15951]
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Peter Dimov
2002-10-17 13:23:11 +00:00
parent f2f616a95c
commit ae60bcaffb
1 changed files with 23 additions and 24 deletions
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shared_ptr.htm
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@ -47,8 +47,8 @@
where <STRONG>U</STRONG> is an accessible base of <STRONG>T</STRONG>, and to <STRONG>
shared_ptr&lt;void&gt;</STRONG>.</P>
<h2><a name="BestPractices">Best Practices</a></h2>
<P>A simple guideline that nearly eliminates the possibility of memory leaks
is: always use a named smart pointer variable to hold the result of <STRONG>new. </STRONG>
<P>A simple guideline that nearly eliminates the possibility of memory leaks is:
always use a named smart pointer variable to hold the result of <STRONG>new. </STRONG>
Every occurence of the <STRONG>new</STRONG> keyword in the code should have the
form:</P>
<PRE>shared_ptr&lt;T&gt; p(new Y);</PRE>
@ -172,7 +172,7 @@ void bad()
<p><b>Exception safety:</b> If an exception is thrown, the constructor has no
effect.</p>
</blockquote>
<P><EM>[The poscondition of use_count() == 1 is too strong. Having the nothrow
<P><EM>[The postcondition of use_count() == 1 is too strong. Having the nothrow
guarantee is important, since <STRONG>reset()</STRONG> is specified in terms of
the default constructor, but the current specification requires that a count be
allocated. Therefore, this postcondition will be dropped in a future release.
@ -221,15 +221,15 @@ void bad()
<P><EM> Another possible implementation is to use a global pointer-to-count map instead
of intrusive counting. <STRONG>shared_from_this</STRONG> would no longer be
O(1), which is a concern for some users, although I do not expect any
performance problems, since the operation is rare. Maintaining a global
map is difficult; it needs to be initialized before any <STRONG>shared_ptr</STRONG>
instances are constructed, and the initialization needs to be thread safe.
In addition, under the Windows dynamic library model, it is possible for
several maps to exist.</EM></P>
performance problems, since the operation is rare. Maintaining a global map is
difficult; it needs to be initialized before any <STRONG>shared_ptr</STRONG> instances
are constructed, and the initialization needs to be thread safe. In addition,
under the Windows dynamic library model, it is possible for several maps to
exist.</EM></P>
<P><EM> It is not yet clear which implementation should be used, or whether the
specification should allow both; nevertheless, the ability to make a <STRONG>shared_ptr</STRONG>
from <STRONG>this</STRONG> is considered essential by experienced smart
pointer users.</EM><EM>]</EM></P>
from <STRONG>this</STRONG> is considered essential by experienced smart pointer
users.</EM><EM>]</EM></P>
<pre>template&lt;typename Y, typename D&gt; shared_ptr(Y * p, D d);</pre>
<blockquote>
<p><b>Requirements:</b> <B>p</B> must be convertible to <B>T *</B>. <STRONG>D</STRONG>
@ -263,8 +263,7 @@ void bad()
requires an overload set that breaks on many compilers due to 14.5.5.2 problems
(and of course it will break on compilers that don't do partial ordering at
all.)</EM></P>
<P><EM>The requrement will be removed when the aforementioned issues are
resolved.]</EM></P>
<P><EM>The requrement will be removed when the aforementioned issues are resolved.]</EM></P>
<pre>shared_ptr(shared_ptr const &amp; r); // never throws
template&lt;typename Y&gt; shared_ptr(shared_ptr&lt;Y&gt; const &amp; r); // never throws</pre>
<blockquote>
@ -336,7 +335,7 @@ q = p;
<p>both assignments may be no-ops.</p>
</BLOCKQUOTE>
<P><EM>[Some experts consider the note to be redundant, as it appears to essentially
mirror the "as if" rile. However, experience suggests that when C++ code is
mirror the "as if" rule. However, experience suggests that when C++ code is
used to describe effects, it is often misinterpreted as required
implementation. In addition, it is not entirely clear whether the "as if" rule
actually applies here, so it's better to be explicit about the possible
@ -398,8 +397,8 @@ q = p;
<h3><a name="conversions">conversions</a></h3>
<pre>operator <i>unspecified-bool-type</i> () const; // never throws</pre>
<blockquote>
<p><b>Returns:</b> an unspecified value that, when used in boolean contexts,
is equivalent to <code>get() != 0</code>.</p>
<p><b>Returns:</b> an unspecified value that, when used in boolean contexts, is
equivalent to <code>get() != 0</code>.</p>
<p><b>Throws:</b> nothing.</p>
<P><B>Notes:</B> This conversion operator allows <b>shared_ptr</b> objects to be
used in boolean contexts, like <code>if (p &amp;&amp; p-&gt;valid()) {}</code>.
@ -432,9 +431,9 @@ q = p;
<pre>template&lt;typename T&gt;
bool operator&lt;(shared_ptr&lt;T&gt; const &amp; a, shared_ptr&lt;T&gt; const &amp; b); // never throws</pre>
<blockquote>
<p><b>Returns:</b> an unspecified value such that <b>operator&lt;</b> is a
strict weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code>
of the C++ standard.</p>
<p><b>Returns:</b> an unspecified value such that <b>operator&lt;</b> is a strict
weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code> of
the C++ standard.</p>
<p><b>Throws:</b> nothing.</p>
<P><B>Notes:</B> Allows <STRONG>shared_ptr</STRONG> objects to be used as keys in
associative containers.</P>
@ -555,12 +554,12 @@ q = p;
type.</p>
<h2><a name="ThreadSafety">Thread Safety</a></h2>
<p><STRONG>shared_ptr</STRONG> objects offer the same level of thread safety as
built-in types. A <STRONG>shared_ptr</STRONG> instance can be "read"
(accessed using only const operations) simultaneously by multiple threads.
Different <STRONG>shared_ptr</STRONG> instances can be "written to" (accessed
using mutable operations such as <STRONG>operator= </STRONG>or <STRONG>reset</STRONG>)
simultaneosly by multiple threads (even when these instances are copies, and
share the same reference count underneath.)</p>
built-in types. A <STRONG>shared_ptr</STRONG> instance can be "read" (accessed
using only const operations) simultaneously by multiple threads. Different <STRONG>shared_ptr</STRONG>
instances can be "written to" (accessed using mutable operations such as <STRONG>operator=
</STRONG>or <STRONG>reset</STRONG>) simultaneosly by multiple threads (even
when these instances are copies, and share the same reference count
underneath.)</p>
<P>Any other simultaneous accesses result in undefined behavior.</P>
<P>Examples:</P>
<pre>