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Implement a long-standing request to support tuning the size of the emergency buffer for allocating exceptions after malloc fails, or to disable that buffer entirely. It's now possible to disable the dynamic allocation of the buffer and use a fixed-size static buffer, via --enable-libstdcxx-static-eh-pool. This is a built-time choice that is baked into libstdc++ and so affects all code linked against that build of libstdc++. The size of the pool can be set by --with-libstdcxx-eh-pool-obj-count=N which is measured in units of sizeof(void*) not bytes. A given exception type such as std::system_error depends on the target, so giving a size in bytes wouldn't be portable across 16/32/64-bit targets. When libstdc++ is configured to use a dynamic buffer, the size of that buffer can now be tuned at runtime by setting the GLIBCXX_TUNABLES environment variable (c.f. PR libstdc++/88264). The number of exceptions to reserve space for is controlled by the "glibcxx.eh_pool.obj_count" and "glibcxx.eh_pool.obj_size" tunables. The pool will be sized to be able to allocate obj_count exceptions of size obj_size*sizeof(void*) and obj_count "dependent" exceptions rethrown by std::rethrow_exception. With the ability to tune the buffer size, we can reduce the default pool size on 32-bit and 16-bit targets. Most users never need to throw 1kB exceptions in parallel from hundreds of threads after malloc is OOM. The users who do need that can use the tunables to select larger sizes. The old defaults can be chosen at runtime by setting GLIBCXX_TUNABLES to: 64-bit: glibcxx.eh_pool.obj_count=64:glibcxx.eh_pool.obj_size=112 32-bit: glibcxx.eh_pool.obj_count=32:glibcxx.eh_pool.obj_size=104 Or approximated by configuring with: 64-bit: --with-libstdcxx-eh-pool-obj-count=252 32-bit: --with-libstdcxx-eh-pool-obj-count=94 libstdc++-v3/ChangeLog: PR libstdc++/68606 * Makefile.in: Regenerate. * acinclude.m4 (GLIBCXX_EMERGENCY_EH_ALLOC): New macro. * configure: Regenerate. * configure.ac: Use GLIBCXX_EMERGENCY_EH_ALLOC. * crossconfig.m4: Check for secure_getenv. * doc/Makefile.in: Regenerate. * doc/xml/manual/configure.xml: Document new configure options. * doc/xml/manual/evolution.xml: Document addition of tunables. * doc/xml/manual/using_exceptions.xml: Document emergency buffer and tunables. * doc/html/*: Regenerate. * include/Makefile.in: Regenerate. * libsupc++/Makefile.am: Use EH_POOL_FLAGS. * libsupc++/Makefile.in: Regenerate. * libsupc++/eh_alloc.cc (EMERGENCY_OBJ_SIZE): Define in units of sizeof(void*) not including the ABI's exception header. (EMERGENCY_OBJ_COUNT): Define as target-independent calculation based on word size. (MAX_OBJ_COUNT): Define macro for upper limit on pool size. (pool) [_GLIBCXX_EH_POOL_STATIC]: Use fixed-size buffer. (pool::buffer_size_in_bytes): New static member function. (pool::pool): Parse GLIBCXX_TUNABLES environment variable to set pool size at runtime. (pool::in_pool): Use std::less<void*> for total order. (__freeres) [_GLIBCXX_EH_POOL_STATIC]: Do nothing. (__cxa_free_exception, __cxa_free_dependent_exception): Add [[unlikely]] attributes. * po/Makefile.in: Regenerate. * python/Makefile.in: Regenerate. * src/Makefile.in: Regenerate. * src/c++11/Makefile.in: Regenerate. * src/c++17/Makefile.in: Regenerate. * src/c++20/Makefile.in: Regenerate. * src/c++98/Makefile.in: Regenerate. * src/filesystem/Makefile.in: Regenerate. * src/libbacktrace/Makefile.in: Regenerate. * testsuite/Makefile.in: Regenerate.
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Part IV. Appendices</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="index.html" title="The GNU C++ Library Manual" /><link rel="prev" href="ext_concurrency_use.html" title="Use" /><link rel="next" href="appendix_contributing.html" title="Appendix A. Contributing" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Part IV.
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Appendices
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</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ext_concurrency_use.html">Prev</a> </td><th width="60%" align="center">The GNU C++ Library Manual</th><td width="20%" align="right"> <a accesskey="n" href="appendix_contributing.html">Next</a></td></tr></table><hr /></div><div class="part"><div class="titlepage"><div><div><h1 class="title"><a id="appendix"></a>Part IV.
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Appendices
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</h1></div></div></div><div class="toc"><p><strong>Table of Contents</strong></p><dl class="toc"><dt><span class="appendix"><a href="appendix_contributing.html">A.
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Contributing
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</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_contributing.html#contrib.list">Contributor Checklist</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_contributing.html#list.reading">Reading</a></span></dt><dt><span class="section"><a href="appendix_contributing.html#list.copyright">Assignment</a></span></dt><dt><span class="section"><a href="appendix_contributing.html#list.getting">Getting Sources</a></span></dt><dt><span class="section"><a href="appendix_contributing.html#list.patches">Submitting Patches</a></span></dt></dl></dd><dt><span class="section"><a href="source_organization.html">Directory Layout and Source Conventions</a></span></dt><dt><span class="section"><a href="source_code_style.html">Coding Style</a></span></dt><dd><dl><dt><span class="section"><a href="source_code_style.html#coding_style.bad_identifiers">Bad Identifiers</a></span></dt><dt><span class="section"><a href="source_code_style.html#coding_style.example">By Example</a></span></dt></dl></dd><dt><span class="section"><a href="source_design_notes.html">Design Notes</a></span></dt></dl></dd><dt><span class="appendix"><a href="appendix_porting.html">B.
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Porting and Maintenance
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</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_porting.html#appendix.porting.build_hacking">Configure and Build Hacking</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_porting.html#build_hacking.prereq">Prerequisites</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.overview">Overview</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_porting.html#build_hacking.overview.basic">General Process</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.overview.map">What Comes from Where</a></span></dt></dl></dd><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure">Configure</a></span></dt><dd><dl><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure.scripts">Storing Information in non-AC files (like configure.host)</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure.conventions">Coding and Commenting Conventions</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure.acinclude">The acinclude.m4 layout</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure.enable"><code class="constant">GLIBCXX_ENABLE</code>, the <code class="literal">--enable</code> maker</a></span></dt><dt><span class="section"><a href="appendix_porting.html#build_hacking.configure.version">Shared Library Versioning</a></span></dt></dl></dd><dt><span class="section"><a href="appendix_porting.html#build_hacking.make">Make</a></span></dt></dl></dd><dt><span class="section"><a href="documentation_hacking.html">Writing and Generating Documentation</a></span></dt><dd><dl><dt><span class="section"><a href="documentation_hacking.html#doc.intro">Introduction</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#doc.generation">Generating Documentation</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#doc.doxygen">Doxygen</a></span></dt><dd><dl><dt><span class="section"><a href="documentation_hacking.html#doxygen.prereq">Prerequisites</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#doxygen.rules">Generating the Doxygen Files</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#doxygen.debug">Debugging Generation</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#doxygen.markup">Markup</a></span></dt></dl></dd><dt><span class="section"><a href="documentation_hacking.html#doc.docbook">Docbook</a></span></dt><dd><dl><dt><span class="section"><a href="documentation_hacking.html#docbook.prereq">Prerequisites</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#docbook.rules">Generating the DocBook Files</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#docbook.debug">Debugging Generation</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#docbook.validation">Editing and Validation</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#docbook.examples">File Organization and Basics</a></span></dt><dt><span class="section"><a href="documentation_hacking.html#docbook.markup">Markup By Example</a></span></dt></dl></dd></dl></dd><dt><span class="section"><a href="internals.html">Porting to New Hardware or Operating Systems</a></span></dt><dd><dl><dt><span class="section"><a href="internals.html#internals.os">Operating System</a></span></dt><dt><span class="section"><a href="internals.html#internals.cpu">CPU</a></span></dt><dt><span class="section"><a href="internals.html#internals.char_types">Character Types</a></span></dt><dt><span class="section"><a href="internals.html#internals.thread_safety">Thread Safety</a></span></dt><dt><span class="section"><a href="internals.html#internals.numeric_limits">Numeric Limits</a></span></dt><dt><span class="section"><a href="internals.html#internals.libtool">Libtool</a></span></dt></dl></dd><dt><span class="section"><a href="test.html">Testing</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.organization">Test Organization</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.organization.layout">Directory Layout</a></span></dt><dt><span class="section"><a href="test.html#test.organization.naming">Naming Conventions</a></span></dt></dl></dd><dt><span class="section"><a href="test.html#test.run">Running the Testsuite</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.run.basic">Basic</a></span></dt><dt><span class="section"><a href="test.html#test.run.variations">Variations</a></span></dt><dt><span class="section"><a href="test.html#test.run.permutations">Permutations</a></span></dt></dl></dd><dt><span class="section"><a href="test.html#test.new_tests">Writing a new test case</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#tests.dg.examples">Examples of Test Directives</a></span></dt><dt><span class="section"><a href="test.html#tests.dg.directives">Directives Specific to Libstdc++ Tests</a></span></dt></dl></dd><dt><span class="section"><a href="test.html#test.harness">Test Harness and Utilities</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.harness.dejagnu">DejaGnu Harness Details</a></span></dt><dt><span class="section"><a href="test.html#test.harness.utils">Utilities</a></span></dt></dl></dd><dt><span class="section"><a href="test.html#test.special">Special Topics</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.exception.safety">
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Qualifying Exception Safety Guarantees
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</a></span></dt><dd><dl><dt><span class="section"><a href="test.html#test.exception.safety.overview">Overview</a></span></dt><dt><span class="section"><a href="test.html#test.exception.safety.status">
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Existing tests
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</a></span></dt><dt><span class="section"><a href="test.html#test.exception.safety.containers">
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C++11 Requirements Test Sequence Descriptions
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</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="section"><a href="abi.html">ABI Policy and Guidelines</a></span></dt><dd><dl><dt><span class="section"><a href="abi.html#abi.cxx_interface">The C++ Interface</a></span></dt><dt><span class="section"><a href="abi.html#abi.versioning">Versioning</a></span></dt><dd><dl><dt><span class="section"><a href="abi.html#abi.versioning.goals">Goals</a></span></dt><dt><span class="section"><a href="abi.html#abi.versioning.history">History</a></span></dt><dt><span class="section"><a href="abi.html#abi.versioning.prereq">Prerequisites</a></span></dt><dt><span class="section"><a href="abi.html#abi.versioning.config">Configuring</a></span></dt><dt><span class="section"><a href="abi.html#abi.versioning.active">Checking Active</a></span></dt></dl></dd><dt><span class="section"><a href="abi.html#abi.changes_allowed">Allowed Changes</a></span></dt><dt><span class="section"><a href="abi.html#abi.changes_no">Prohibited Changes</a></span></dt><dt><span class="section"><a href="abi.html#abi.impl">Implementation</a></span></dt><dt><span class="section"><a href="abi.html#abi.testing">Testing</a></span></dt><dd><dl><dt><span class="section"><a href="abi.html#abi.testing.single">Single ABI Testing</a></span></dt><dt><span class="section"><a href="abi.html#abi.testing.multi">Multiple ABI Testing</a></span></dt></dl></dd><dt><span class="section"><a href="abi.html#abi.issues">Outstanding Issues</a></span></dt></dl></dd><dt><span class="section"><a href="api.html">API Evolution and Deprecation History</a></span></dt><dd><dl><dt><span class="section"><a href="api.html#api.rel_300"><code class="constant">3.0</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_310"><code class="constant">3.1</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_320"><code class="constant">3.2</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_330"><code class="constant">3.3</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_340"><code class="constant">3.4</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_400"><code class="constant">4.0</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_410"><code class="constant">4.1</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_420"><code class="constant">4.2</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_430"><code class="constant">4.3</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_440"><code class="constant">4.4</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_450"><code class="constant">4.5</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_460"><code class="constant">4.6</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_470"><code class="constant">4.7</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_480"><code class="constant">4.8</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_490"><code class="constant">4.9</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_51"><code class="constant">5</code></a></span></dt><dd><dl><dt><span class="section"><a href="api.html#api.rel_53"><code class="constant">5.3</code></a></span></dt></dl></dd><dt><span class="section"><a href="api.html#api.rel_61"><code class="constant">6</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_71"><code class="constant">7</code></a></span></dt><dd><dl><dt><span class="section"><a href="api.html#api.rel_72"><code class="constant">7.2</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_73"><code class="constant">7.3</code></a></span></dt></dl></dd><dt><span class="section"><a href="api.html#api.rel_81"><code class="constant">8</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_91"><code class="constant">9</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_101"><code class="constant">10</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_111"><code class="constant">11</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_121"><code class="constant">12</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_123"><code class="constant">12.3</code></a></span></dt><dt><span class="section"><a href="api.html#api.rel_131"><code class="constant">13</code></a></span></dt></dl></dd><dt><span class="section"><a href="backwards.html">Backwards Compatibility</a></span></dt><dd><dl><dt><span class="section"><a href="backwards.html#backwards.first">First</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.second">Second</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third">Third</a></span></dt><dd><dl><dt><span class="section"><a href="backwards.html#backwards.third.headers">Pre-ISO headers removed</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.hash">Extension headers hash_map, hash_set moved to ext or backwards</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.nocreate_noreplace">No <code class="code">ios::nocreate/ios::noreplace</code>.
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</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.streamattach">
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No <code class="code">stream::attach(int fd)</code>
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</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.support_cxx98">
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Support for C++98 dialect.
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</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.support_tr1">
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Support for C++TR1 dialect.
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</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.support_cxx11">
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Support for C++11 dialect.
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</a></span></dt><dt><span class="section"><a href="backwards.html#backwards.third.iterator_type">
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<code class="code">Container::iterator_type</code> is not necessarily <code class="code">Container::value_type*</code>
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</a></span></dt></dl></dd></dl></dd></dl></dd><dt><span class="appendix"><a href="appendix_free.html">C.
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Free Software Needs Free Documentation
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</a></span></dt><dt><span class="appendix"><a href="appendix_gpl.html">D.
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<acronym class="acronym">GNU</acronym> General Public License version 3
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</a></span></dt><dt><span class="appendix"><a href="appendix_gfdl.html">E. GNU Free Documentation License</a></span></dt></dl></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ext_concurrency_use.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="index.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="appendix_contributing.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Use </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Appendix A.
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Contributing
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