Add compiler/platform agnostic thread-local storage

It doesn't cover all cases, but we can work on those as
we go along. For now, gcc, MSVC++, Intel C/C++, IBM XL C/C++,
Sun Studio C/C++ and Borland C++ Builder are the supported
compilers (although we boldly assume that they all are of
a recent enough version to support thread-local storage).

This is intended to be used in upcoming patches that implement
graceful (but TLS-dependant) error-handling in the library.

As an added bonus, we also bring the online_cpus() function
from git.git to detect the number of usable cpu's.

Signed-off-by: Andreas Ericsson <ae@op5.se>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

src/git/thread-utils.h

+#ifndef INCLUDE_git_thread_utils_h__
+#define INCLUDE_git_thread_utils_h__
+/*
+ * How TLS works is compiler+platform dependant
+ * Sources: http://en.wikipedia.org/wiki/Thread-Specific_Storage
+ *          http://predef.sourceforge.net/precomp.html
+ */
+#define GIT_HAS_TLS 1
+#if defined(__GNUC__) || defined(__SUNPRO_C) || defined(__SUNPRO_CC) || \
+	defined(__xlc__) || defined(__xlC__)
+# define GIT_TLS __thread
+#elif defined(__INTEL_COMPILER)
+# if defined(_WIN32) || defined(_WIN32_CE)
+#  define GIT_TLS __declspec(thread)
+# else
+#  define GIT_TLS __thread
+# endif
+#elif defined(_WIN32) || defined(_WIN32_CE) || defined(__BORLANDC__)
+# define GIT_TLS __declspec(thread)
+#else
+# undef GIT_HAS_TLS
+# define GIT_TLS /* nothing: tls vars are thread-global */
+#endif
+
+#endif /* INCLUDE_git_thread_utils_h__ */

src/thread-utils.c

+#include "thread-utils.h"
+
+#ifdef _WIN32
+#  define WIN32_LEAN_AND_MEAN
+#  include <windows.h>
+#elif defined(hpux) || defined(__hpux) || defined(_hpux)
+#  include <sys/pstat.h>
+#endif
+
+/*
+ * By doing this in two steps we can at least get
+ * the function to be somewhat coherent, even
+ * with this disgusting nest of #ifdefs.
+ */
+#ifndef _SC_NPROCESSORS_ONLN
+#  ifdef _SC_NPROC_ONLN
+#    define _SC_NPROCESSORS_ONLN _SC_NPROC_ONLN
+#  elif defined _SC_CRAY_NCPU
+#    define _SC_NPROCESSORS_ONLN _SC_CRAY_NCPU
+#  endif
+#endif
+
+int git_online_cpus(void)
+{
+#ifdef _SC_NPROCESSORS_ONLN
+	long ncpus;
+#endif
+
+#ifdef _WIN32
+	SYSTEM_INFO info;
+	GetSystemInfo(&info);
+
+	if ((int)info.dwNumberOfProcessors > 0)
+		return (int)info.dwNumberOfProcessors;
+#elif defined(hpux) || defined(__hpux) || defined(_hpux)
+	struct pst_dynamic psd;
+
+	if (!pstat_getdynamic(&psd, sizeof(psd), (size_t)1, 0))
+		return (int)psd.psd_proc_cnt;
+#endif
+
+#ifdef _SC_NPROCESSORS_ONLN
+	if ((ncpus = (long)sysconf(_SC_NPROCESSORS_ONLN)) > 0)
+		return (int)ncpus;
+#endif
+
+	return 1;
+}

src/thread-utils.h

+#ifndef INCLUDE_thread_utils_h__
+#define INCLUDE_thread_utils_h__
+
+#include "git/thread-utils.h"
+
+extern int git_online_cpus(void);
+
+#endif /* INCLUDE_thread_utils_h__ */