Fix clogged up git operations.

src/main.zig

@@ -6,6 +6,7 @@
 //! else — process management, rendering, and the GTK4 UI — lives here.
 
 const std = @import("std");
+const builtin = @import("builtin");
 const adw = @import("adw");
 const gio = @import("gio");
 
@@ -21,10 +22,28 @@ pub const std_options: std.Options = .{
     .log_level = .info,
 };
 
-var gpa: std.heap.DebugAllocator(.{}) = .init;
+/// The process allocator, which everything in the app shares: the GTK main
+/// loop, every terminal's parser, and every review connection thread.
+///
+/// `DebugAllocator` only in a debug build, and this is not a matter of taste.
+/// It is thread-safe by way of one mutex around every allocation and every
+/// free, and its backing allocator is the page allocator — so a large
+/// allocation is an `mmap` and its release an `munmap`, both taken under that
+/// single process-wide lock. A review pane's poll allocates a whole `git diff`
+/// and drops it a moment later, several times a second across a handful of open
+/// reviews, and each one of those was stalling the main loop and every other
+/// request behind the same lock. `c_allocator` has a per-thread cache and no
+/// global lock; libc is already linked for GTK.
+var debug_gpa: std.heap.DebugAllocator(.{}) = .init;
+
+fn gpa() std.mem.Allocator {
+    return if (builtin.mode == .Debug) debug_gpa.allocator() else std.heap.c_allocator;
+}
 
 pub fn main() u8 {
-    defer _ = gpa.deinit();
+    defer if (builtin.mode == .Debug) {
+        _ = debug_gpa.deinit();
+    };
 
     // Before the allocator's own teardown, since the settings arena comes out
     // of it. A no-op if the app never got as far as activating.
@@ -51,7 +70,7 @@ pub fn main() u8 {
 fn onActivate(app: *adw.Application, _: ?*anyopaque) callconv(.c) void {
     // The file both of the next two read from: the scheme, and the tabs the
     // window opens itself with.
-    Settings.init(gpa.allocator());
+    Settings.init(gpa());
 
     // Before the window, so that the first frame is drawn in the scheme the
     // user chose rather than repainted into it a moment later.
@@ -65,9 +84,9 @@ fn onActivate(app: *adw.Application, _: ?*anyopaque) callconv(.c) void {
     // created and every terminal is handed the endpoint of the tab it opens in.
     // Started unconditionally rather than on the first review pane, so an agent
     // running in a tab has a `PLAYPEN_REVIEW_URL` from the moment it starts.
-    review.init(gpa.allocator());
+    review.init(gpa());
 
-    const window = Window.create(gpa.allocator(), app) catch |err| {
+    const window = Window.create(gpa(), app) catch |err| {
         std.log.err("failed to create window: {s}", .{@errorName(err)});
         return;
     };