[tor-commits] [tor/master] Use mach_approximate_time() for coarse time where available.

[nickm@xxxxxxxxxxxxxx]

commit 021fdd39e4ebbe8ddee9b10823af76fbb11e7878
Author: Nick Mathewson <nickm@xxxxxxxxxxxxxx>
Date:   Fri Dec 8 09:24:02 2017 -0500

    Use mach_approximate_time() for coarse time where available.
    
    This lets us have a coarse-time implementation with reasonable
    performance characteristics on OSX and iOS.
    
    Implements 24427.
---
 changes/feature24427     |  5 +++++
 configure.ac             |  1 +
 src/common/compat_time.c | 15 +++++++++++++++
 src/common/compat_time.h |  3 +++
 4 files changed, 24 insertions(+)

diff --git a/changes/feature24427 b/changes/feature24427
new file mode 100644
index 000000000..8650c45d3
--- /dev/null
+++ b/changes/feature24427
@@ -0,0 +1,5 @@
+  o Minor features (OSX, iOS, performance):
+    - Use the mach_approximate_time() function (when available) to
+      implement coarse monotonic time. Having a coarse time function
+      should avoid a large number of system calls, and improve
+      performance slightly, especially under load. Closes ticket 24427.
diff --git a/configure.ac b/configure.ac
index 0b3e1dda2..84ae9090b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -506,6 +506,7 @@ AC_CHECK_FUNCS(
         llround \
         localtime_r \
         lround \
+	mach_approximate_time \
         memmem \
         memset_s \
 	pipe \
diff --git a/src/common/compat_time.c b/src/common/compat_time.c
index 204b8d7d1..c0cd73c74 100644
--- a/src/common/compat_time.c
+++ b/src/common/compat_time.c
@@ -314,6 +314,21 @@ monotime_get(monotime_t *out)
   out->abstime_ = mach_absolute_time();
 }
 
+#if defined(HAVE_MACH_APPROXIMATE_TIME)
+void
+monotime_coarse_get(monotime_coarse_t *out)
+{
+#ifdef TOR_UNIT_TESTS
+  if (monotime_mocking_enabled) {
+    out->abstime_ = (mock_time_nsec_coarse * mach_time_info.denom)
+      / mach_time_info.numer;
+    return;
+  }
+#endif /* defined(TOR_UNIT_TESTS) */
+  out->abstime_ = mach_approximate_time();
+}
+#endif
+
 /**
  * Return the number of nanoseconds between <b>start</b> and <b>end</b>.
  */
diff --git a/src/common/compat_time.h b/src/common/compat_time.h
index 462dcecce..bcf469e27 100644
--- a/src/common/compat_time.h
+++ b/src/common/compat_time.h
@@ -65,6 +65,9 @@ typedef struct monotime_t {
 typedef struct monotime_coarse_t {
   uint64_t tick_count_;
 } monotime_coarse_t;
+#elif defined(__APPLE__) && defined(HAVE_MACH_APPROXIMATE_TIME)
+#define MONOTIME_COARSE_FN_IS_DIFFERENT
+#define monotime_coarse_t monotime_t
 #else
 #define monotime_coarse_t monotime_t
 #endif /* defined(CLOCK_MONOTONIC_COARSE) && ... || ... */



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