sys/unix: cache time zone info

src/offset/sys/unix.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use std::sync::Once;
+
 use super::{DateTime, FixedOffset, Local, NaiveDateTime};
 use crate::offset::tz_info::TimeZone;
 use crate::Utc;
@@ -27,11 +29,17 @@ pub(super) fn naive_to_local(d: &NaiveDateTime, local: bool) -> DateTime<Local>
 }
 
 fn offset(unix: i64) -> FixedOffset {
+    let info = unsafe {
+        INIT.call_once(|| {
+            INFO = TimeZone::local().expect("unable to parse localtime info");
+        });
+        &INFO
+    };
+
     FixedOffset::east(
-        TimeZone::local()
-            .expect("unable to parse localtime info")
-            .find_local_time_type(unix)
-            .expect("unable to select local time type")
-            .offset(),
+        info.find_local_time_type(unix).expect("unable to select local time type").offset(),
     )
 }
+
+static mut INFO: TimeZone = TimeZone::empty();
+static INIT: Once = Once::new();

src/offset/tz_info/timezone.rs

@@ -100,7 +100,7 @@ impl TimeZone {
     }
 
     /// Construct the time zone associated to UTC
-    fn utc() -> Self {
+    pub(crate) fn utc() -> Self {
         Self {
             transitions: Vec::new(),
             local_time_types: vec![LocalTimeType::UTC],
@@ -109,6 +109,15 @@ impl TimeZone {
         }
     }
 
+    pub(crate) const fn empty() -> Self {
+        Self {
+            transitions: Vec::new(),
+            local_time_types: Vec::new(),
+            leap_seconds: Vec::new(),
+            extra_rule: None,
+        }
+    }
+
     /// Find the local time type associated to the time zone at the specified Unix time in seconds
     pub(crate) fn find_local_time_type(&self, unix_time: i64) -> Result<&LocalTimeType, Error> {
         self.as_ref().find_local_time_type(unix_time)