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| author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
|---|---|---|
| committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
| commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
| tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libstdc++-v3/doc/html/manual/bk01pt03ch19s05.html | |
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Diffstat (limited to 'libstdc++-v3/doc/html/manual/bk01pt03ch19s05.html')
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diff --git a/libstdc++-v3/doc/html/manual/bk01pt03ch19s05.html b/libstdc++-v3/doc/html/manual/bk01pt03ch19s05.html new file mode 100644 index 000000000..2d072f0b4 --- /dev/null +++ b/libstdc++-v3/doc/html/manual/bk01pt03ch19s05.html @@ -0,0 +1,51 @@ +<?xml version="1.0" encoding="UTF-8" standalone="no"?> +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Implementation Issues</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" C++ , library , profile "/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="profile_mode.html" title="Chapter 19. Profile Mode"/><link rel="prev" href="bk01pt03ch19s04.html" title="Empirical Cost Model"/><link rel="next" href="bk01pt03ch19s06.html" title="Developer Information"/></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Implementation Issues</th></tr><tr><td align="left"><a accesskey="p" href="bk01pt03ch19s04.html">Prev</a> </td><th width="60%" align="center">Chapter 19. Profile Mode</th><td align="right"> <a accesskey="n" href="bk01pt03ch19s06.html">Next</a></td></tr></table><hr/></div><div class="section" title="Implementation Issues"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.profile_mode.implementation"/>Implementation Issues</h2></div></div></div><div class="section" title="Stack Traces"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.stack"/>Stack Traces</h3></div></div></div><p> + Accurate stack traces are needed during profiling since we group events by + call context and dynamic instance. Without accurate traces, diagnostics + may be hard to interpret. For instance, when giving advice to the user + it is imperative to reference application code, not library code. + </p><p> + Currently we are using the libc <code class="code">backtrace</code> routine to get + stack traces. + <code class="code">_GLIBCXX_PROFILE_STACK_DEPTH</code> can be set + to 0 if you are willing to give up call context information, or to a small + positive value to reduce run time overhead. + </p></div><div class="section" title="Symbolization of Instruction Addresses"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.symbols"/>Symbolization of Instruction Addresses</h3></div></div></div><p> + The profiling and analysis phases use only instruction addresses. + An external utility such as addr2line is needed to postprocess the result. + We do not plan to add symbolization support in the profile extension. + This would require access to symbol tables, debug information tables, + external programs or libraries and other system dependent information. + </p></div><div class="section" title="Concurrency"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.concurrency"/>Concurrency</h3></div></div></div><p> + Our current model is simplistic, but precise. + We cannot afford to approximate because some of our diagnostics require + precise matching of operations to container instance and call context. + During profiling, we keep a single information table per diagnostic. + There is a single lock per information table. + </p></div><div class="section" title="Using the Standard Library in the Instrumentation Implementation"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.stdlib-in-proflib"/>Using the Standard Library in the Instrumentation Implementation</h3></div></div></div><p> + As much as we would like to avoid uses of libstdc++ within our + instrumentation library, containers such as unordered_map are very + appealing. We plan to use them as long as they are named properly + to avoid ambiguity. + </p></div><div class="section" title="Malloc Hooks"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.malloc-hooks"/>Malloc Hooks</h3></div></div></div><p> + User applications/libraries can provide malloc hooks. + When the implementation of the malloc hooks uses stdlibc++, there can + be an infinite cycle between the profile mode instrumentation and the + malloc hook code. + </p><p> + We protect against reentrance to the profile mode instrumentation code, + which should avoid this problem in most cases. + The protection mechanism is thread safe and exception safe. + This mechanism does not prevent reentrance to the malloc hook itself, + which could still result in deadlock, if, for instance, the malloc hook + uses non-recursive locks. + XXX: A definitive solution to this problem would be for the profile extension + to use a custom allocator internally, and perhaps not to use libstdc++. + </p></div><div class="section" title="Construction and Destruction of Global Objects"><div class="titlepage"><div><div><h3 class="title"><a id="manual.ext.profile_mode.implementation.construction-destruction"/>Construction and Destruction of Global Objects</h3></div></div></div><p> + The profiling library state is initialized at the first call to a profiling + method. This allows us to record the construction of all global objects. + However, we cannot do the same at destruction time. The trace is written + by a function registered by <code class="code">atexit</code>, thus invoked by + <code class="code">exit</code>. + </p></div></div><div class="navfooter"><hr/><table width="100%" summary="Navigation footer"><tr><td align="left"><a accesskey="p" href="bk01pt03ch19s04.html">Prev</a> </td><td align="center"><a accesskey="u" href="profile_mode.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch19s06.html">Next</a></td></tr><tr><td align="left" valign="top">Empirical Cost Model </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Developer Information</td></tr></table></div></body></html> |