diff options
| -rw-r--r-- | libc/bionic/system_properties.cpp | 10 | ||||
| -rw-r--r-- | libc/include/sys/_system_properties.h | 18 |
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 |