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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> where <STRONG>U</STRONG> is an accessible base of <STRONG>T</STRONG>, and to <STRONG>
shared_ptr&lt;void&gt;</STRONG>.</P> shared_ptr&lt;void&gt;</STRONG>.</P>
<h2><a name="BestPractices">Best Practices</a></h2> <h2><a name="BestPractices">Best Practices</a></h2>
<P>A simple guideline that nearly eliminates the possibility of memory leaks <P>A simple guideline that nearly eliminates the possibility of memory leaks is:
is: always use a named smart pointer variable to hold the result of <STRONG>new. </STRONG> 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 Every occurence of the <STRONG>new</STRONG> keyword in the code should have the
form:</P> form:</P>
<PRE>shared_ptr&lt;T&gt; p(new Y);</PRE> <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 <p><b>Exception safety:</b> If an exception is thrown, the constructor has no
effect.</p> effect.</p>
</blockquote> </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 guarantee is important, since <STRONG>reset()</STRONG> is specified in terms of
the default constructor, but the current specification requires that a count be the default constructor, but the current specification requires that a count be
allocated. Therefore, this postcondition will be dropped in a future release. 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 <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 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 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 performance problems, since the operation is rare. Maintaining a global map is
map is difficult; it needs to be initialized before any <STRONG>shared_ptr</STRONG> difficult; it needs to be initialized before any <STRONG>shared_ptr</STRONG> instances
instances are constructed, and the initialization needs to be thread safe. are constructed, and the initialization needs to be thread safe. In addition,
In addition, under the Windows dynamic library model, it is possible for under the Windows dynamic library model, it is possible for several maps to
several maps to exist.</EM></P> exist.</EM></P>
<P><EM> It is not yet clear which implementation should be used, or whether the <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> specification should allow both; nevertheless, the ability to make a <STRONG>shared_ptr</STRONG>
from <STRONG>this</STRONG> is considered essential by experienced smart from <STRONG>this</STRONG> is considered essential by experienced smart pointer
pointer users.</EM><EM>]</EM></P> users.</EM><EM>]</EM></P>
<pre>template&lt;typename Y, typename D&gt; shared_ptr(Y * p, D d);</pre> <pre>template&lt;typename Y, typename D&gt; shared_ptr(Y * p, D d);</pre>
<blockquote> <blockquote>
<p><b>Requirements:</b> <B>p</B> must be convertible to <B>T *</B>. <STRONG>D</STRONG> <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 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 (and of course it will break on compilers that don't do partial ordering at
all.)</EM></P> all.)</EM></P>
<P><EM>The requrement will be removed when the aforementioned issues are <P><EM>The requrement will be removed when the aforementioned issues are resolved.]</EM></P>
resolved.]</EM></P>
<pre>shared_ptr(shared_ptr const &amp; r); // never throws <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> template&lt;typename Y&gt; shared_ptr(shared_ptr&lt;Y&gt; const &amp; r); // never throws</pre>
<blockquote> <blockquote>
@ -336,7 +335,7 @@ q = p;
<p>both assignments may be no-ops.</p> <p>both assignments may be no-ops.</p>
</BLOCKQUOTE> </BLOCKQUOTE>
<P><EM>[Some experts consider the note to be redundant, as it appears to essentially <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 used to describe effects, it is often misinterpreted as required
implementation. In addition, it is not entirely clear whether the "as if" rule 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 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> <h3><a name="conversions">conversions</a></h3>
<pre>operator <i>unspecified-bool-type</i> () const; // never throws</pre> <pre>operator <i>unspecified-bool-type</i> () const; // never throws</pre>
<blockquote> <blockquote>
<p><b>Returns:</b> an unspecified value that, when used in boolean contexts, <p><b>Returns:</b> an unspecified value that, when used in boolean contexts, is
is equivalent to <code>get() != 0</code>.</p> equivalent to <code>get() != 0</code>.</p>
<p><b>Throws:</b> nothing.</p> <p><b>Throws:</b> nothing.</p>
<P><B>Notes:</B> This conversion operator allows <b>shared_ptr</b> objects to be <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>. 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; <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> bool operator&lt;(shared_ptr&lt;T&gt; const &amp; a, shared_ptr&lt;T&gt; const &amp; b); // never throws</pre>
<blockquote> <blockquote>
<p><b>Returns:</b> an unspecified value such that <b>operator&lt;</b> is a <p><b>Returns:</b> an unspecified value such that <b>operator&lt;</b> is a strict
strict weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code> weak ordering as described in section 25.3 <code>[lib.alg.sorting]</code> of
of the C++ standard.</p> the C++ standard.</p>
<p><b>Throws:</b> nothing.</p> <p><b>Throws:</b> nothing.</p>
<P><B>Notes:</B> Allows <STRONG>shared_ptr</STRONG> objects to be used as keys in <P><B>Notes:</B> Allows <STRONG>shared_ptr</STRONG> objects to be used as keys in
associative containers.</P> associative containers.</P>
@ -555,12 +554,12 @@ q = p;
type.</p> type.</p>
<h2><a name="ThreadSafety">Thread Safety</a></h2> <h2><a name="ThreadSafety">Thread Safety</a></h2>
<p><STRONG>shared_ptr</STRONG> objects offer the same level of thread safety as <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" built-in types. A <STRONG>shared_ptr</STRONG> instance can be "read" (accessed
(accessed using only const operations) simultaneously by multiple threads. using only const operations) simultaneously by multiple threads. Different <STRONG>shared_ptr</STRONG>
Different <STRONG>shared_ptr</STRONG> instances can be "written to" (accessed instances can be "written to" (accessed using mutable operations such as <STRONG>operator=
using mutable operations such as <STRONG>operator= </STRONG>or <STRONG>reset</STRONG>) </STRONG>or <STRONG>reset</STRONG>) simultaneosly by multiple threads (even
simultaneosly by multiple threads (even when these instances are copies, and when these instances are copies, and share the same reference count
share the same reference count underneath.)</p> underneath.)</p>
<P>Any other simultaneous accesses result in undefined behavior.</P> <P>Any other simultaneous accesses result in undefined behavior.</P>
<P>Examples:</P> <P>Examples:</P>
<pre> <pre>