From 79bf71d23437a33eaf4ce27f2d325d21508bb45e Mon Sep 17 00:00:00 2001
From: Ian Jackson <ijackson@chiark.greenend.org.uk>
Date: Fri, 9 Apr 2021 17:27:10 +0100
Subject: [PATCH] locks: Make config an Option

This makes it plausible to implement ConstDefault for it.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>
---
 src/config.rs  | 20 +++++++++++++++++---
 src/global.rs  |  2 +-
 src/prelude.rs |  1 +
 3 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/src/config.rs b/src/config.rs
index cc6d1292..38b7dab9 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -191,15 +191,29 @@ impl TryFrom<ServerConfigSpec> for WholeServerConfig {
   }
 }
 
+fn config_read() -> MappedRwLockReadGuard<'static, WholeServerConfig> {
+  {
+    let g = GLOBAL.config.read();
+    let g = RwLockReadGuard::try_map(g, |g| g.as_ref());
+    if let Ok(g) = g { return g }
+  }
+  {
+    let mut g = GLOBAL.config.write();
+    g.get_or_insert_with(default);
+    let g = RwLockWriteGuard::downgrade(g);
+    RwLockReadGuard::try_map(g, |g| g.as_ref()).unwrap()
+  }
+}
+
 pub fn config() -> Arc<ServerConfig> {
-  GLOBAL.config.read().server.clone()
+  config_read().server.clone()
 }
 pub fn log_config() -> LogSpecification {
-  GLOBAL.config.read().log.clone()
+  config_read().log.clone()
 }
 
 fn set_config(whole: WholeServerConfig) {
-  *GLOBAL.config.write() = whole;
+  *GLOBAL.config.write() = Some(whole);
 }
 
 impl ServerConfig {
diff --git a/src/global.rs b/src/global.rs
index 1e33ace8..44b258c1 100644
--- a/src/global.rs
+++ b/src/global.rs
@@ -206,7 +206,7 @@ pub struct Global {
   // <- InstanceContainer ->
   // inner locks which the game needs:
   dirty: Mutex<VecDeque<InstanceRef>>,
-  pub config: RwLock<WholeServerConfig>,
+  pub config: RwLock<Option<WholeServerConfig>>,
 
   // fast global lookups
   players: RwLock<TokenTable<PlayerId>>,
diff --git a/src/prelude.rs b/src/prelude.rs
index 7911b6b7..96432335 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -77,6 +77,7 @@ pub use num_traits::{Bounded, FromPrimitive, ToPrimitive};
 pub use ordered_float::OrderedFloat;
 pub use parking_lot::{Condvar, Mutex, MutexGuard};
 pub use parking_lot::{RwLock, RwLockReadGuard, RwLockWriteGuard};
+pub use parking_lot::{MappedRwLockReadGuard};
 pub use percent_encoding::percent_decode_str;
 pub use percent_encoding::utf8_percent_encode;
 pub use percent_encoding::NON_ALPHANUMERIC;
-- 
2.30.2