From 972d063ea1e7c11acdc2bf0f8f894f3e82b68357 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alexandre=20Mondaini=20Calv=C3=A3o?= <apotema@gmail.com>
Date: Fri, 2 Oct 2026 15:43:34 -0300
Subject: [PATCH] fix(wasm): keep synchronous pathfinding off browser pthread
 pool

---
 src/floyd_warshall_optimized.zig | 8 +++++++-
 src/nav/floyd_warshall.zig       | 5 ++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/floyd_warshall_optimized.zig b/src/floyd_warshall_optimized.zig
index 41491af..11c9c33 100644
--- a/src/floyd_warshall_optimized.zig
+++ b/src/floyd_warshall_optimized.zig
@@ -9,6 +9,7 @@
 //! source-destination queries.
 
 const std = @import("std");
+const builtin = @import("builtin");
 
 const INF: u32 = std.math.maxInt(u32);
 
@@ -223,7 +224,12 @@ pub fn FloydWarshallOptimized(comptime config: Config) type {
 
         /// Run the Floyd-Warshall algorithm to compute all shortest paths
         pub fn generate(self: *Self) void {
-            if (config.parallel and self.size > 64) {
+            // Browser pthread pools are shared with persistent engine workers.
+            // This synchronous spawn/join algorithm cannot reserve a worker
+            // budget there; CPU discovery also uses unsupported sysctlbyname
+            // in Zig 0.16's Emscripten libc implementation. Keep web on SIMD
+            // until pathfinding can use an asynchronous, budgeted job API.
+            if (config.parallel and !builtin.single_threaded and builtin.os.tag != .emscripten and self.size > 64) {
                 self.generateParallel();
             } else if (config.simd) {
                 self.generateSimd();
diff --git a/src/nav/floyd_warshall.zig b/src/nav/floyd_warshall.zig
index eea72b5..f8bb955 100644
--- a/src/nav/floyd_warshall.zig
+++ b/src/nav/floyd_warshall.zig
@@ -1,4 +1,5 @@
 const std = @import("std");
+const builtin = @import("builtin");
 const types = @import("types.zig");
 const graph_mod = @import("graph.zig");
 const zig_utils = @import("zig_utils");
@@ -15,7 +16,9 @@ const U32_INF: u32 = std.math.maxInt(u32);
 
 /// Optimized FW backend: SIMD + multi-threading via zig-utils.
 const FWOptimized = zig_utils.FloydWarshallOptimized(.{
-    .parallel = true,
+    // The synchronous zig-utils implementation cannot reserve workers from
+    // the browser's shared pthread pool. Use SIMD on threaded web too.
+    .parallel = !builtin.single_threaded and builtin.os.tag != .emscripten,
     .simd = true,
 });