When built with NO_PTHREADS, the macros are used make the code build
even though pthreads header and library may be missing. The code can
still have different code paths for no threads support with
HAVE_THREADS variable.
There are of course impacts on no-pthreads builds:
- data structure may get slightly bigger because all the mutexes and
pthread_t are present (as an int)
- code execution is not impacted much. Locking (in hot path) is
no-op. Other wrapper function calls really should not matter much.
- the binary size grows bigger because of threaded code. But at least
on Linux this does not matter, if some code is not executed, it's
not mapped in memory.
This is a preparation step to remove "#ifdef NO_PTHREADS" in the code
mostly because of maintainability. As Jeff put it
> it's probably OK to stop thinking of it as "non-threaded platforms
> are the default and must pay zero cost" and more as "threaded
> platforms are the default, and non-threaded ones are OK to pay a
> small cost as long as they still work".
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Under NO_PTHREADS build, we warn when delta_search_threads is not
set to 1, because that is the only sensible value on a single
threaded build.
However, the auto detection that kicks in when that variable is set
to 0 (e.g. there is no configuration variable or command line option,
or an explicit --threads=0 is given from the command line to override
the pack.threads configuration to force auto-detection) was not done
before the condition to issue this warning was tested.
Move the auto-detection code and place it at an appropriate spot.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All files that include this header file use the same four line
incantation:
#ifndef NO_PTHREADS
#include <pthread.h>
#include "thread-utils.h"
#endif
Move the responsibility for that gymnastics to the header file from the
files that include it. This approach makes it easier to later declare new
services that are related to threading in thread-utils.h and have them
available to all the threading code.
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The mutex used to protect object access (read_mutex) may need to be
acquired recursively. Introduce init_recursive_mutex() helper function
in thread-utils.c that constructs a mutex with the PHREAD_MUTEX_RECURSIVE
attribute.
pthread_mutex_init() emulation on Win32 is already recursive as it is
implemented on top of the CRITICAL_SECTION type, which is recursive.
http://msdn.microsoft.com/en-us/library/ms682530%28VS.85%29.aspx
Add do-nothing compatibility wrappers for pthread_mutexattr* functions.
Initial-version-by: Fredrik Kuivinen <frekui@gmail.com>
Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Packing objects can be done in parallell nowadays, but it's
only done if the config option pack.threads is set to a value
above 1. Because of that, the code-path used is often not the
most optimal one.
This patch adds a routine to detect the number of online CPU's
at runtime (online_cpus()). When pack.threads (or --threads=) is
given a value of 0, the number of threads is set to the number of
online CPU's. This feature is also documented.
As per Nicolas Pitre's recommendations, the default is still to
run pack-objects single-threaded unless explicitly activated,
either by configuration or by command line parameter.
The routine online_cpus() is a rework of "numcpus.c", written by
one Philip Willoughby <pgw99@doc.ic.ac.uk>. numcpus.c is in the
public domain and can presently be downloaded from
http://csgsoft.doc.ic.ac.uk/numcpus/
Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
