Re: time to ticks converter optimization in pthread_cond_timedwait

[Jonathan Larmour <jifl at eCosCentric dot com>]

Wade Jensen wrote:
> Hello,
>  
> Here is a patch that makes a simple optimization in 
> pthread_cond_timedwait.  It will only initialize the time to ticks 
> converters on the first call the same way that is done many other places 
> in the code.  It greatly improves the speed of the 
> pthread_cond_timedwait function.
For some reason although I got your patch, and made a few tweaks myself, I 
never checked it in. I'm doing so now (attached).

Jifl
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Index: ChangeLog
===================================================================
RCS file: /cvs/ecos/ecos/packages/compat/posix/current/ChangeLog,v
retrieving revision 1.30
diff -u -5 -p -r1.30 ChangeLog
--- ChangeLog	26 Nov 2002 18:16:45 -0000	1.30
+++ ChangeLog	10 Dec 2002 02:26:53 -0000
@@ -1,5 +1,11 @@
+2002-12-10  Wade Jensen  <waj4news@cox.net>
+2002-12-10  Jonathan Larmour  <jifl@eCosCentric.com>
+
+	* src/mutex.cxx (pthread_cond_timedwait): Initialize clock converters
+	only once ever.
+
 2002-11-26  Nick Garnett  <nickg@ecoscentric.com>
 
 	* src/signal.cxx: Changed the three routines added in the last
 	change so that they can be called safely from non-POSIX threads.
 
Index: src/mutex.cxx
===================================================================
RCS file: /cvs/ecos/ecos/packages/compat/posix/current/src/mutex.cxx,v
retrieving revision 1.3
diff -u -5 -p -r1.3 mutex.cxx
--- src/mutex.cxx	23 May 2002 22:59:59 -0000	1.3
+++ src/mutex.cxx	10 Dec 2002 02:26:53 -0000
@@ -39,11 +39,11 @@
 //####ECOSGPLCOPYRIGHTEND####
 //==========================================================================
 //#####DESCRIPTIONBEGIN####
 //
 // Author(s):           nickg
-// Contributors:        nickg, jlarmour
+// Contributors:        nickg, jlarmour, Wade Jensen
 // Date:                2000-03-27
 // Purpose:             POSIX pthread implementation
 // Description:         This file contains the implementation of the POSIX pthread
 //                      functions.
 //              
@@ -498,16 +498,41 @@ externC int pthread_cond_timedwait (pthr
 
     PTHREAD_CHECK( cond );
     PTHREAD_CHECK( mutex );    
     PTHREAD_CHECK( abstime );    
 
-    cyg_tick_count ticks;
-    struct Cyg_Clock::converter ns_converter, sec_converter;
-    
-    Cyg_Clock::real_time_clock->get_other_to_clock_converter( 1, &ns_converter );
-    Cyg_Clock::real_time_clock->get_other_to_clock_converter( 1000000000, &sec_converter );
+    // Only initialize the converters once or they will consume a huge
+    // amount or runtime.
+
+    static struct Cyg_Clock::converter ns_converter;
+    static struct Cyg_Clock::converter sec_converter;
+    static volatile cyg_atomic conv_init;
+    if (!conv_init)
+    {
 
+        // Try to avoid unnecessarily locking the scheduler when we are not
+        // initializing the converters.  Check the conv_init flag again to
+        // avoid race conditions.
+
+        struct Cyg_Clock::converter temp_ns_converter, temp_sec_converter;
+    
+        Cyg_Clock::real_time_clock
+            ->get_other_to_clock_converter( 1, &temp_ns_converter );
+        Cyg_Clock::real_time_clock
+            ->get_other_to_clock_converter( 1000000000, &temp_sec_converter );
+
+        Cyg_Scheduler::lock();
+        if (!conv_init)
+        {
+            ns_converter = temp_ns_converter;
+            sec_converter = temp_sec_converter;
+            conv_init=1;
+        }
+        Cyg_Scheduler::unlock();
+    }
+
+    cyg_tick_count ticks;
     ticks = Cyg_Clock::convert( abstime->tv_sec, &sec_converter );
     ticks += Cyg_Clock::convert( abstime->tv_nsec, &ns_converter );
     
     ((Cyg_Condition_Variable *)cond)->wait( *(Cyg_Mutex *)mutex, ticks );