feat: Support retrieving WriterStrategyBuilder from VortexSession (#6)

* Fix session get-or-default (vortex-data#5662)

The comments described this get-or-default, but instead it was a panic

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Signed-off-by: Nicholas Gates <nick@nickgates.com>

* feat: Support retrieving writer strategy builder from vortex session

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Signed-off-by: Nicholas Gates <nick@nickgates.com>
Co-authored-by: Nicholas Gates <gatesn@users.noreply.github.com>

Author: 2 people

vortex-session/src/lib.rs

@@ -3,20 +3,14 @@
 
 pub mod registry;
 
-use std::any::Any;
-use std::any::TypeId;
-use std::any::type_name;
+use std::any::{Any, TypeId, type_name};
 use std::fmt::Debug;
-use std::hash::BuildHasherDefault;
-use std::hash::Hasher;
-use std::ops::Deref;
-use std::ops::DerefMut;
+use std::hash::{BuildHasherDefault, Hasher};
+use std::ops::{Deref, DerefMut};
 use std::sync::Arc;
 
-use dashmap::DashMap;
-use dashmap::Entry;
-use vortex_error::VortexExpect;
-use vortex_error::vortex_panic;
+use dashmap::{DashMap, Entry};
+use vortex_error::{VortexExpect, vortex_panic};
 
 /// A Vortex session encapsulates the set of extensible arrays, layouts, compute functions, dtypes,
 /// etc. that are available for use in a given context.
@@ -108,18 +102,6 @@ impl SessionExt for VortexSession {
 
     /// Returns the scope variable of type `V`, or inserts a default one if it does not exist.
     fn get<V: SessionVar + Default>(&self) -> Ref<'_, V> {
-        // NOTE(ngates): we don't use `entry().or_insert_with_key()` here because the DashMap
-        //  would immediately acquire an exclusive write lock.
-        if let Some(v) = self.0.get(&TypeId::of::<V>()) {
-            return Ref(v.map(|v| {
-                (**v)
-                    .as_any()
-                    .downcast_ref::<V>()
-                    .vortex_expect("Type mismatch - this is a bug")
-            }));
-        }
-
-        // If we get here, the value was not present, so we insert the default with a write lock.
         Ref(self
             .0
             .entry(TypeId::of::<V>())