Improve the performance when writing Index files

In response to issue #60 (git_index_write really slow), the write_index
function has been rewritten to improve its performance -- it should now
be in par with the performance of git.git.

On top of that, if Posix Threads are available when compiling libgit2, a
new threaded writing system will be used (3 separate threads take care
of solving byte-endianness, hashing the contents of the index and
writing to disk, respectively). For very long Index files, this method
is up to 3x times faster than git.git.

Signed-off-by: Vicent Marti <tanoku@gmail.com>

1 files changed, 88 insertions, 68 deletions

diff --git a/src/thread-utils.h b/src/thread-utils.h
index 0395b97d1..588c919bf 100644
--- a/src/thread-utils.h
+++ b/src/thread-utils.h
@@ -2,86 +2,106 @@
 #define INCLUDE_thread_utils_h__
 
 #if defined(GIT_HAS_PTHREAD)
-typedef pthread_mutex_t git_lck;
-# define GITLCK_INIT      PTHREAD_MUTEX_INITIALIZER
-# define gitlck_init(a)   pthread_mutex_init(a, NULL)
-# define gitlck_lock(a)   pthread_mutex_lock(a)
-# define gitlck_unlock(a) pthread_mutex_unlock(a)
-# define gitlck_free(a)   pthread_mutex_destroy(a)
+	typedef pthread_t git_thread;
+#	define git_thread_create(thread, attr, start_routine, arg) pthread_create(thread, attr, start_routine, arg)
+#	define git_thread_kill(thread) pthread_cancel(thread)
+#	define git_thread_exit(status)	pthread_exit(status)
+#	define git_thread_join(id, status) pthread_join(id, status)
 
-# if defined(GIT_HAS_ASM_ATOMIC)
-#  include <asm/atomic.h>
-typedef atomic_t git_refcnt;
-#  define gitrc_init(a)   atomic_set(a, 0)
-#  define gitrc_inc(a)    atomic_inc_return(a)
-#  define gitrc_dec(a)    atomic_dec_and_test(a)
-#  define gitrc_free(a)   (void)0
+	/* Pthreads Mutex */
+	typedef pthread_mutex_t git_lck;
+#	define GITLCK_INIT      PTHREAD_MUTEX_INITIALIZER
+#	define gitlck_init(a)   pthread_mutex_init(a, NULL)
+#	define gitlck_lock(a)   pthread_mutex_lock(a)
+#	define gitlck_unlock(a) pthread_mutex_unlock(a)
+#	define gitlck_free(a)   pthread_mutex_destroy(a)
 
-# else
-typedef struct { git_lck lock; int counter; } git_refcnt;
+	/* Pthreads condition vars */
+	typedef pthread_cond_t git_cnd;
+#	define GITCND_INIT			PTHREAD_COND_INITIALIZER
+#	define gitcnd_init(c, a)	pthread_cond_init(c, a)
+#	define gitcnd_free(c)		pthread_cond_destroy(c)
+#	define gitcnd_wait(c, l)	pthread_cond_wait(c, l)
+#	define gitcnd_signal(c)		pthread_cond_signal(c)
+#	define gitcnd_broadcast(c)	pthread_cond_broadcast(c)
 
-/** Initialize to 0.  No memory barrier is issued. */
-GIT_INLINE(void) gitrc_init(git_refcnt *p)
-{
-	gitlck_init(&p->lock);
-	p->counter = 0;
-}
+#	if defined(GIT_HAS_ASM_ATOMIC)
+#		include <asm/atomic.h>
+		typedef atomic_t git_refcnt;
+#		define gitrc_init(a, v) atomic_set(a, v)
+#		define gitrc_inc(a)		atomic_inc_return(a)
+#		define gitrc_dec(a)		atomic_dec_and_test(a)
+#		define gitrc_free(a)	(void)0
+#	elif defined(GIT_WIN32)
+		typedef long git_refcnt;
+#		define gitrc_init(a, v)	*a = v
+#		define gitrc_inc(a)		InterlockedIncrement(a)
+#		define gitrc_dec(a)		!InterlockedDecrement(a)
+#		define gitrc_free(a)	(void)0
+#	else
+		typedef struct { git_lck lock; int counter; } git_refcnt;
 
-/**
- * Increment.
- *
- * Atomically increments @p by 1.  A memory barrier is also
- * issued before and after the operation.
- *
- * @param p pointer of type git_refcnt
- */
-GIT_INLINE(void) gitrc_inc(git_refcnt *p)
-{
-	gitlck_lock(&p->lock);
-	p->counter++;
-	gitlck_unlock(&p->lock);
-}
+		/** Initialize to 0.  No memory barrier is issued. */
+		GIT_INLINE(void) gitrc_init(git_refcnt *p, int value)
+		{
+			gitlck_init(&p->lock);
+			p->counter = value;
+		}
 
-/**
- * Decrement and test.
- *
- * Atomically decrements @p by 1 and returns true if the
- * result is 0, or false for all other cases.  A memory
- * barrier is also issued before and after the operation.
- *
- * @param p pointer of type git_refcnt
- */
-GIT_INLINE(int) gitrc_dec(git_refcnt *p)
-{
-	int c;
-	gitlck_lock(&p->lock);
-	c = --p->counter;
-	gitlck_unlock(&p->lock);
-	return !c;
-}
+		/**
+		 * Increment.
+		 *
+		 * Atomically increments @p by 1.  A memory barrier is also
+		 * issued before and after the operation.
+		 *
+		 * @param p pointer of type git_refcnt
+		 */
+		GIT_INLINE(void) gitrc_inc(git_refcnt *p)
+		{
+			gitlck_lock(&p->lock);
+			p->counter++;
+			gitlck_unlock(&p->lock);
+		}
 
-/** Free any resources associated with the counter. */
-#  define gitrc_free(p) gitlck_free(&(p)->lock)
+		/**
+		 * Decrement and test.
+		 *
+		 * Atomically decrements @p by 1 and returns true if the
+		 * result is 0, or false for all other cases.  A memory
+		 * barrier is also issued before and after the operation.
+		 *
+		 * @param p pointer of type git_refcnt
+		 */
+		GIT_INLINE(int) gitrc_dec(git_refcnt *p)
+		{
+			int c;
+			gitlck_lock(&p->lock);
+			c = --p->counter;
+			gitlck_unlock(&p->lock);
+			return !c;
+		}
 
-# endif
+		/** Free any resources associated with the counter. */
+#		define gitrc_free(p) gitlck_free(&(p)->lock)
+#	endif
 
 #elif defined(GIT_THREADS)
-# error GIT_THREADS but no git_lck implementation
+#	error GIT_THREADS but no git_lck implementation
 
 #else
-typedef struct { int dummy; } git_lck;
-# define GIT_MUTEX_INIT   {}
-# define gitlck_init(a)   (void)0
-# define gitlck_lock(a)   (void)0
-# define gitlck_unlock(a) (void)0
-# define gitlck_free(a)   (void)0
-
-typedef struct { int counter; } git_refcnt;
-# define gitrc_init(a)   ((a)->counter = 0)
-# define gitrc_inc(a)    ((a)->counter++)
-# define gitrc_dec(a)    (--(a)->counter == 0)
-# define gitrc_free(a)   (void)0
+	/* no threads support */
+	typedef struct { int dummy; } git_lck;
+#	define GIT_MUTEX_INIT   {}
+#	define gitlck_init(a)   (void)0
+#	define gitlck_lock(a)   (void)0
+#	define gitlck_unlock(a) (void)0
+#	define gitlck_free(a)   (void)0
 
+	typedef struct { int counter; } git_refcnt;
+#	define gitrc_init(a)   ((a)->counter = 0)
+#	define gitrc_inc(a)    ((a)->counter++)
+#	define gitrc_dec(a)    (--(a)->counter == 0)
+#	define gitrc_free(a)   (void)0
 #endif
 
 extern int git_online_cpus(void);