zed: Allocate more rayon threads depending on available parallelism (#43235)

Lukas Wirth created 

While zed itself is not a heavy user of rayon, wasmtime is, especially
for compilation. This change is similar to the rayon default but we
halve the number of threads still so we don't spawn too many threads
overall.

Release Notes:

- N/A *or* Added/Fixed/Improved ...

Change summary

crates/remote_server/src/unix.rs | 2 +-
crates/zed/src/main.rs           | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

Detailed changes

crates/remote_server/src/unix.rs 🔗 

@@ -373,7 +373,7 @@ pub fn execute_run(
     let listeners = ServerListeners::new(stdin_socket, stdout_socket, stderr_socket)?;
 
     rayon::ThreadPoolBuilder::new()
-        .num_threads(4)
+        .num_threads(std::thread::available_parallelism().map_or(1, |n| n.get().div_ceil(2)))
         .stack_size(10 * 1024 * 1024)
         .thread_name(|ix| format!("RayonWorker{}", ix))
         .build_global()

crates/zed/src/main.rs 🔗 

@@ -265,7 +265,7 @@ pub fn main() {
     }
 
     rayon::ThreadPoolBuilder::new()
-        .num_threads(4)
+        .num_threads(std::thread::available_parallelism().map_or(1, |n| n.get().div_ceil(2)))
         .stack_size(10 * 1024 * 1024)
         .thread_name(|ix| format!("RayonWorker{}", ix))
         .build_global()