diff --git a/.github/actions/install/action.yml b/.github/actions/install/action.yml
index c18090bb..c59bc9a9 100644
--- a/.github/actions/install/action.yml
+++ b/.github/actions/install/action.yml
@@ -22,6 +22,10 @@ inputs:
     description: 'cache dir to use'
     required: false
     default: '~/.cache'
+  debug:
+    description: 'enable v8 pre-built debug version, only available for linux x86_64'
+    required: false
+    default: 'false'
 
 runs:
   using: "composite"
@@ -47,17 +51,17 @@ runs:
         cache-name: cache-v8
       with:
         path: ${{ inputs.cache-dir }}/v8
-        key: libc_v8_${{ inputs.v8 }}_${{ inputs.os }}_${{ inputs.arch }}_${{ inputs.zig-v8 }}.a
+        key: libc_v8_${{ inputs.v8 }}_${{ inputs.os }}_${{ inputs.arch }}_${{ inputs.zig-v8 }}${{inputs.debug == 'true' && '_debug' || '' }}.a
 
     - if: ${{ steps.cache-v8.outputs.cache-hit != 'true' }}
       shell: bash
       run: |
         mkdir -p ${{ inputs.cache-dir }}/v8
 
-        wget -O ${{ inputs.cache-dir }}/v8/libc_v8.a https://github.com/lightpanda-io/zig-v8-fork/releases/download/${{ inputs.zig-v8 }}/libc_v8_${{ inputs.v8 }}_${{ inputs.os }}_${{ inputs.arch }}.a
+        wget -O ${{ inputs.cache-dir }}/v8/libc_v8.a https://github.com/lightpanda-io/zig-v8-fork/releases/download/${{ inputs.zig-v8 }}/libc_v8_${{ inputs.v8 }}_${{ inputs.os }}_${{ inputs.arch }}${{inputs.debug == 'true' && '_debug' || '' }}.a
 
     - name: install v8
       shell: bash
       run: |
         mkdir -p v8
-        ln -s ${{ inputs.cache-dir }}/v8/libc_v8.a v8/libc_v8.a
+        ln -s ${{ inputs.cache-dir }}/v8/libc_v8.a v8/libc_v8${{inputs.debug == 'true' && '_debug' || '' }}.a
diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 8edd1fc5..d2bcde3b 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -40,7 +40,6 @@ jobs:
         with:
           os: ${{env.OS}}
           arch: ${{env.ARCH}}
-          mode: 'release'
 
       - name: v8 snapshot
         run: zig build -Dprebuilt_v8_path=v8/libc_v8.a -Doptimize=ReleaseFast snapshot_creator -- src/snapshot.bin
@@ -83,7 +82,6 @@ jobs:
         with:
           os: ${{env.OS}}
           arch: ${{env.ARCH}}
-          mode: 'release'
 
       - name: v8 snapshot
         run: zig build -Dprebuilt_v8_path=v8/libc_v8.a -Doptimize=ReleaseFast snapshot_creator -- src/snapshot.bin
@@ -128,7 +126,6 @@ jobs:
         with:
           os: ${{env.OS}}
           arch: ${{env.ARCH}}
-          mode: 'release'
 
       - name: v8 snapshot
         run: zig build -Dprebuilt_v8_path=v8/libc_v8.a -Doptimize=ReleaseFast snapshot_creator -- src/snapshot.bin
@@ -171,7 +168,6 @@ jobs:
         with:
           os: ${{env.OS}}
           arch: ${{env.ARCH}}
-          mode: 'release'
 
       - name: v8 snapshot
         run: zig build -Dprebuilt_v8_path=v8/libc_v8.a -Doptimize=ReleaseFast snapshot_creator -- src/snapshot.bin
diff --git a/.github/workflows/e2e-test.yml b/.github/workflows/e2e-test.yml
index feb1e04f..87cf9d8e 100644
--- a/.github/workflows/e2e-test.yml
+++ b/.github/workflows/e2e-test.yml
@@ -56,8 +56,6 @@ jobs:
           submodules: recursive
 
       - uses: ./.github/actions/install
-        with:
-          mode: 'release'
 
       - name: zig build release
         run: zig build -Dprebuilt_v8_path=v8/libc_v8.a -Doptimize=ReleaseFast -Dcpu=x86_64 -Dgit_commit=$(git rev-parse --short ${{ github.sha }})
diff --git a/.github/workflows/zig-test.yml b/.github/workflows/zig-test.yml
index 3e05c7e5..d1b01046 100644
--- a/.github/workflows/zig-test.yml
+++ b/.github/workflows/zig-test.yml
@@ -38,6 +38,26 @@ on:
   workflow_dispatch:
 
 jobs:
+  zig-test-debug:
+    name: zig test using v8 in debug mode
+    timeout-minutes: 15
+
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+          # fetch submodules recusively, to get zig-js-runtime submodules also.
+          submodules: recursive
+
+      - uses: ./.github/actions/install
+        with:
+          debug: true
+
+      - name: zig build test
+        run: zig build -Dprebuilt_v8_path=v8/libc_v8_debug.a -Dtsan=true test
+
   zig-test:
     name: zig test
     timeout-minutes: 15
diff --git a/src/TestHTTPServer.zig b/src/TestHTTPServer.zig
index 9750a396..19c5bbc9 100644
--- a/src/TestHTTPServer.zig
+++ b/src/TestHTTPServer.zig
@@ -20,7 +20,7 @@ const std = @import("std");
 
 const TestHTTPServer = @This();
 
-shutdown: bool,
+shutdown: std.atomic.Value(bool),
 listener: ?std.net.Server,
 handler: Handler,
 
@@ -28,16 +28,22 @@ const Handler = *const fn (req: *std.http.Server.Request) anyerror!void;
 
 pub fn init(handler: Handler) TestHTTPServer {
     return .{
-        .shutdown = true,
+        .shutdown = .init(true),
         .listener = null,
         .handler = handler,
     };
 }
 
 pub fn deinit(self: *TestHTTPServer) void {
-    self.shutdown = true;
+    self.listener = null;
+}
+
+pub fn stop(self: *TestHTTPServer) void {
+    self.shutdown.store(true, .release);
     if (self.listener) |*listener| {
-        listener.deinit();
+        // Use shutdown to unblock accept(). On Linux this causes accept to
+        // return error.SocketNotListening. close() alone doesn't interrupt accept().
+        std.posix.shutdown(listener.stream.handle, .recv) catch {};
     }
 }
 
@@ -46,12 +52,13 @@ pub fn run(self: *TestHTTPServer, wg: *std.Thread.WaitGroup) !void {
 
     self.listener = try address.listen(.{ .reuse_address = true });
     var listener = &self.listener.?;
+    self.shutdown.store(false, .release);
 
     wg.finish();
 
     while (true) {
         const conn = listener.accept() catch |err| {
-            if (self.shutdown) {
+            if (self.shutdown.load(.acquire) or err == error.SocketNotListening) {
                 return;
             }
             return err;
diff --git a/src/test_runner.zig b/src/test_runner.zig
index 2461c82f..1b9a2324 100644
--- a/src/test_runner.zig
+++ b/src/test_runner.zig
@@ -442,6 +442,7 @@ pub const TrackingAllocator = struct {
     allocated_bytes: usize = 0,
     allocation_count: usize = 0,
     reallocation_count: usize = 0,
+    mutex: std.Thread.Mutex = .{},
 
     const Stats = struct {
         allocated_bytes: usize,
@@ -479,6 +480,9 @@ pub const TrackingAllocator = struct {
         return_address: usize,
     ) ?[*]u8 {
         const self: *TrackingAllocator = @ptrCast(@alignCast(ctx));
+        self.mutex.lock();
+        defer self.mutex.unlock();
+
         const result = self.parent_allocator.rawAlloc(len, alignment, return_address);
         self.allocation_count += 1;
         self.allocated_bytes += len;
@@ -493,6 +497,9 @@ pub const TrackingAllocator = struct {
         ra: usize,
     ) bool {
         const self: *TrackingAllocator = @ptrCast(@alignCast(ctx));
+        self.mutex.lock();
+        defer self.mutex.unlock();
+
         const result = self.parent_allocator.rawResize(old_mem, alignment, new_len, ra);
         self.reallocation_count += 1; // TODO: only if result is not null?
         return result;
@@ -505,6 +512,9 @@ pub const TrackingAllocator = struct {
         ra: usize,
     ) void {
         const self: *TrackingAllocator = @ptrCast(@alignCast(ctx));
+        self.mutex.lock();
+        defer self.mutex.unlock();
+
         self.parent_allocator.rawFree(old_mem, alignment, ra);
         self.free_count += 1;
     }
@@ -517,6 +527,9 @@ pub const TrackingAllocator = struct {
         ret_addr: usize,
     ) ?[*]u8 {
         const self: *TrackingAllocator = @ptrCast(@alignCast(ctx));
+        self.mutex.lock();
+        defer self.mutex.unlock();
+
         const result = self.parent_allocator.rawRemap(memory, alignment, new_len, ret_addr);
         self.reallocation_count += 1; // TODO: only if result is not null?
         return result;
diff --git a/src/testing.zig b/src/testing.zig
index 05c7efbc..41f67e96 100644
--- a/src/testing.zig
+++ b/src/testing.zig
@@ -450,7 +450,9 @@ const TestHTTPServer = @import("TestHTTPServer.zig");
 
 const Server = @import("Server.zig");
 var test_cdp_server: ?Server = null;
+var test_cdp_server_thread: ?std.Thread = null;
 var test_http_server: ?TestHTTPServer = null;
+var test_http_server_thread: ?std.Thread = null;
 
 var test_config: Config = undefined;
 
@@ -482,16 +484,10 @@ test "tests:beforeAll" {
     var wg: std.Thread.WaitGroup = .{};
     wg.startMany(2);
 
-    {
-        const thread = try std.Thread.spawn(.{}, serveCDP, .{&wg});
-        thread.detach();
-    }
+    test_cdp_server_thread = try std.Thread.spawn(.{}, serveCDP, .{&wg});
 
     test_http_server = TestHTTPServer.init(testHTTPHandler);
-    {
-        const thread = try std.Thread.spawn(.{}, TestHTTPServer.run, .{ &test_http_server.?, &wg });
-        thread.detach();
-    }
+    test_http_server_thread = try std.Thread.spawn(.{}, TestHTTPServer.run, .{ &test_http_server.?, &wg });
 
     // need to wait for the servers to be listening, else tests will fail because
     // they aren't able to connect.
@@ -499,9 +495,22 @@ test "tests:beforeAll" {
 }
 
 test "tests:afterAll" {
+    if (test_cdp_server) |*server| {
+        server.stop();
+    }
+    if (test_cdp_server_thread) |thread| {
+        thread.join();
+    }
     if (test_cdp_server) |*server| {
         server.deinit();
     }
+
+    if (test_http_server) |*server| {
+        server.stop();
+    }
+    if (test_http_server_thread) |thread| {
+        thread.join();
+    }
     if (test_http_server) |*server| {
         server.deinit();
     }
@@ -518,8 +527,6 @@ fn serveCDP(wg: *std.Thread.WaitGroup) !void {
     const address = try std.net.Address.parseIp("127.0.0.1", 9583);
     test_cdp_server = try Server.init(test_app, address);
 
-    var server = try Server.init(test_app, address);
-    defer server.deinit();
     wg.finish();
 
     test_cdp_server.?.run(address, 5) catch |err| {