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libitm: Update texinfo docs. 

Backported from mainline @184940.
	libitm/
	* libitm.texi: Link to specification and add a usage example.

From-SVN: r184954
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Torvald Riegel 2012-03-05 19:26:37 +00:00 committed by Torvald Riegel
parent b7fabe6d57
commit 38cdf40323
2 changed files with 35 additions and 3 deletions
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@ -1,3 +1,7 @@
2012-03-02 Torvald Riegel <triegel@redhat.com>
* libitm.texi: Link to specification and add a usage example.
2012-02-24 Torvald Riegel <triegel@redhat.com>
* retry.cc (GTM::gtm_thread::number_of_threads_changed): Change

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libitm/libitm.texi
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@ -82,8 +82,8 @@ several threads.
To activate support for TM in C/C++, the compile-time flag @option{-fgnu-tm}
must be specified. This enables TM language-level constructs such as
transaction statements (@code{__transaction}, @pxref{C/C++ Language
Constructs for TM} for details).
transaction statements (e.g., @code{__transaction_atomic}, @pxref{C/C++
Language Constructs for TM} for details).
@c ---------------------------------------------------------------------
@c C/C++ Language Constructs for TM
@ -92,7 +92,35 @@ Constructs for TM} for details).
@node C/C++ Language Constructs for TM
@chapter C/C++ Language Constructs for TM
TODO: link to the C++ TM spec. a few examples. how gcc's support differs.
Transactions are supported in C++ and C in the form of transaction statements,
transaction expressions, and function transactions. In the following example,
both @code{a} and @code{b} will be read and the difference will be written to
@code{c}, all atomically and isolated from other transactions:
@example
__transaction_atomic @{ c = a - b; @}
@end example
Therefore, another thread can use the following code to concurrently update
@code{b} without ever causing @code{c} to hold a negative value (and without
having to use other synchronization constructs such as locks or C++11
atomics):
@example
__transaction_atomic @{ if (a > b) b++; @}
@end example
GCC follows the @uref{https://sites.google.com/site/tmforcplusplus/, Draft
Specification of Transactional Language Constructs for C++ (v1.1)} in its
implementation of transactions.
The precise semantics of transactions are defined in terms of the C++11/C11
memory model (see the specification). Roughly, transactions provide
synchronization guarantees that are similar to what would be guaranteed when
using a single global lock as a guard for all transactions. Note that like
other synchronization constructs in C/C++, transactions rely on a
data-race-free program (e.g., a nontransactional write that is concurrent
with a transactional read to the same memory location is a data race).
@c ---------------------------------------------------------------------
@c The libitm ABI