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authorMark Salyzyn <salyzyn@google.com>2015-04-24 09:31:32 -0700
committerMark Salyzyn <salyzyn@google.com>2015-04-28 22:20:41 +0000
commit123927dffc28018a1feb1d42c625b601cb948f34 (patch)
tree905fe666bf92ebcfb4f33a5b71f721c5342ab3d3
parent452742d2bf4247106055696c11bc4e59ca630f11 (diff)
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bionic: add __system_property_area_serial()
Adds a new _internal_ function. Provide a global serial number to support more efficient private caching algorithms. This allows to skip re-running the __system_property_find() call on misses until there is a global change in the properties. This call is a read barrier, the property data to be read following this call will be read sequentially and up to date. (Cherry pick from bfd65279a5a9018b01f71773270e462f1b9a7768) Bug: 19544788 Change-Id: I58e6a92baa0f3e8e7b9ec79b10af6d56407dab48
-rw-r--r--libc/bionic/system_properties.cpp10
-rw-r--r--libc/include/sys/_system_properties.h18
2 files changed, 28 insertions, 0 deletions
diff --git a/libc/bionic/system_properties.cpp b/libc/bionic/system_properties.cpp
index aae99b1..c436a16 100644
--- a/libc/bionic/system_properties.cpp
+++ b/libc/bionic/system_properties.cpp
@@ -598,6 +598,16 @@ int __system_property_area_init()
return map_prop_area_rw();
}
+unsigned int __system_property_area_serial()
+{
+ prop_area *pa = __system_property_area__;
+ if (!pa) {
+ return -1;
+ }
+ // Make sure this read fulfilled before __system_property_serial
+ return atomic_load_explicit(&(pa->serial), memory_order_acquire);
+}
+
const prop_info *__system_property_find(const char *name)
{
if (__predict_false(compat_mode)) {
diff --git a/libc/include/sys/_system_properties.h b/libc/include/sys/_system_properties.h
index 7ff3ded..c200295 100644
--- a/libc/include/sys/_system_properties.h
+++ b/libc/include/sys/_system_properties.h
@@ -98,6 +98,24 @@ int __system_property_set_filename(const char *filename);
*/
int __system_property_area_init();
+/* Read the global serial number of the system properties
+**
+** Called to predict if a series of cached __system_property_find
+** objects will have seen __system_property_serial values change.
+** But also aids the converse, as changes in the global serial can
+** also be used to predict if a failed __system_property_find
+** could in-turn now find an new object; thus preventing the
+** cycles of effort to poll __system_property_find.
+**
+** Called at the beginning of a cache cycle to signal _any_ possible
+** changes have occurred since last. If there is, check each individual
+** __system_property_serial to confirm dirty, or __system_property_find
+** to check if the property now exists.
+**
+** Returns the serial number on success, -1 on error.
+*/
+unsigned int __system_property_area_serial();
+
/* Add a new system property. Can only be done by a single
** process that has write access to the property area, and
** that process must handle sequencing to ensure the property