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authorErlang/OTP <[email protected]>2010-09-13 17:58:05 +0200
committerErlang/OTP <[email protected]>2010-09-13 17:58:05 +0200
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</header>
<p>This document describes the changes made to the STDLIB application.</p>
+<section><title>STDLIB 1.17.1</title>
+
+ <section><title>Fixed Bugs and Malfunctions</title>
+ <list>
+ <item>
+ <p>reference() has been substituted for ref() in the
+ documentation.</p>
+ <p>
+ Own Id: OTP-8733</p>
+ </item>
+ </list>
+ </section>
+
+
+ <section><title>Improvements and New Features</title>
+ <list>
+ <item>
+ <p>
+ The ms_transform now warns if the fun head shadows
+ surrounding variables (just like the warnings you would
+ get for an ordinary fun in the same context).</p>
+ <p>
+ Own Id: OTP-6759</p>
+ </item>
+ <item>
+ <p>
+ ets:select_reverse/{1,2,3} are now documented.</p>
+ <p>
+ Own Id: OTP-7863</p>
+ </item>
+ <item>
+ <p>
+ Large parts of the <c>ethread</c> library have been
+ rewritten. The <c>ethread</c> library is an Erlang
+ runtime system internal, portable thread library used by
+ the runtime system itself.</p>
+ <p>
+ Most notable improvement is a reader optimized rwlock
+ implementation which dramatically improve the performance
+ of read-lock/read-unlock operations on multi processor
+ systems by avoiding ping-ponging of the rwlock cache
+ lines. The reader optimized rwlock implementation is used
+ by miscellaneous rwlocks in the runtime system that are
+ known to be read-locked frequently, and can be enabled on
+ ETS tables by passing the <seealso
+ marker="stdlib:ets#new_2_read_concurrency">{read_concurrency,
+ true}</seealso> option upon table creation. See the
+ documentation of <seealso
+ marker="stdlib:ets#new/2">ets:new/2</seealso> for more
+ information. The reader optimized rwlock implementation
+ can be fine tuned when starting the runtime system. For
+ more information, see the documentation of the <seealso
+ marker="erts:erl#+rg">+rg</seealso> command line argument
+ of <c>erl</c>.</p>
+ <p>
+ There is also a new implementation of rwlocks that is not
+ optimized for readers. Both implementations interleaves
+ readers and writers during contention as opposed to,
+ e.g., the NPTL (Linux) pthread rwlock implementation
+ which use either a reader or writer preferred strategy.
+ The reader/writer preferred strategy is problematic since
+ it starves threads doing the non-preferred operation.</p>
+ <p>
+ The new rwlock implementations in general performs better
+ in ERTS than common pthread implementations. However, in
+ some extremely heavily contended cases this is not the
+ case. Such heavy contention can more or less only appear
+ on ETS tables. This when multiple processes do very large
+ amounts of write locked operations simultaneously on the
+ same table. Such use of ETS is bad regardless of rwlock
+ implementation, will never scale, and is something we
+ strongly advise against.</p>
+ <p>
+ The new rwlock implementations depend on atomic
+ operations. If no native atomic implementation is found,
+ a fallback solution will be used. Using the fallback
+ implies a performance degradation. That is, it is more
+ important now than before to build OTP with a native
+ atomic implementation.</p>
+ <p>
+ The <c>ethread</c> library contains native atomic
+ implementations for, x86 (32 and 64 bit), powerpc (32
+ bit), sparc V9 (32 and 64 bit), and tilera (32 bit). On
+ other hardware gcc's builtin support for atomic memory
+ access will be used if such exists. If no such support is
+ found, <c>configure</c> will warn about no atomic
+ implementation available.</p>
+ <p>
+ The <c>ethread</c> library can now also use the
+ <c>libatomic_ops</c> library for atomic memory accesses.
+ This makes it possible for the Erlang runtime system to
+ utilize optimized native atomic operations on more
+ platforms than before. If <c>configure</c> warns about no
+ atomic implementation available, try using the
+ <c>libatomic_ops</c> library. Use the <seealso
+ marker="doc/installation_guide:INSTALL#How-to-Build-and-Install-ErlangOTP_A-Closer-Look-at-the-individual-Steps_Configuring">--with-libatomic_ops=PATH</seealso>
+ <c>configure</c> command line argument when specifying
+ where the <c>libatomic_ops</c> installation is located.
+ The <c>libatomic_ops</c> library can be downloaded from:
+ <url
+ href="http://www.hpl.hp.com/research/linux/atomic_ops/">http://www.hpl.hp.com/research/linux/atomic_ops/</url></p>
+ <p>
+ The changed API of the <c>ethread</c> library has also
+ caused modifications in the Erlang runtime system.
+ Preparations for the to come "delayed deallocation"
+ feature has also been done since it depends on the
+ <c>ethread</c> library.</p>
+ <p>
+ <em>Note</em>: When building for x86, the <c>ethread</c>
+ library will now use instructions that first appeared on
+ the pentium 4 processor. If you want the runtime system
+ to be compatible with older processors (back to 486) you
+ need to pass the <seealso
+ marker="doc/installation_guide:INSTALL#How-to-Build-and-Install-ErlangOTP_A-Closer-Look-at-the-individual-Steps_Configuring">--enable-ethread-pre-pentium4-compatibility</seealso>
+ <c>configure</c> command line argument when configuring
+ the system.</p>
+ <p>
+ Own Id: OTP-8544</p>
+ </item>
+ <item>
+ <p>
+ Some Built In Functions (BIFs) from the module erlang was
+ never made autoimported for backward compatibility
+ reasons. As local functions now override autoimports, new
+ autoimports is no longer a problem, why the following
+ BIFs are finally made autoimported: monitor/2, monitor/3,
+ demonitor/2, demonitor/3, error/1, error/2,
+ integer_to_list/2, list_to_integer/2.</p>
+ <p>
+ Own Id: OTP-8763</p>
+ </item>
+ </list>
+ </section>
+
+</section>
+
<section><title>STDLIB 1.17</title>
<section><title>Fixed Bugs and Malfunctions</title>