diff --git a/lib/std/Io/Threaded.zig b/lib/std/Io/Threaded.zig
index 4b1ebbc59b..60df1bdd81 100644
--- a/lib/std/Io/Threaded.zig
+++ b/lib/std/Io/Threaded.zig
@@ -29,8 +29,8 @@ const ws2_32 = std.os.windows.ws2_32;
 /// * scanning environment variables on some targets
 /// * memory-mapping when mmap or equivalent is not available
 allocator: Allocator,
-mutex: std.Thread.Mutex = .{},
-cond: std.Thread.Condition = .{},
+mutex: Mutex = .init,
+cond: Condition = .init,
 run_queue: std.SinglyLinkedList = .{},
 join_requested: bool = false,
 stack_size: usize,
@@ -1486,8 +1486,8 @@ var global_single_threaded_instance: Threaded = .init_single_threaded;
 pub const global_single_threaded: *Threaded = &global_single_threaded_instance;
 
 pub fn setAsyncLimit(t: *Threaded, new_limit: Io.Limit) void {
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
     t.async_limit = new_limit;
 }
 
@@ -1508,11 +1508,11 @@ pub fn deinit(t: *Threaded) void {
 fn join(t: *Threaded) void {
     if (builtin.single_threaded) return;
     {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
         t.join_requested = true;
     }
-    t.cond.broadcast();
+    condBroadcast(&t.cond);
     t.wait_group.wait();
 }
 
@@ -1574,20 +1574,20 @@ fn worker(t: *Threaded) void {
 
     defer t.wait_group.finish();
 
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
 
     while (true) {
         while (t.run_queue.popFirst()) |runnable_node| {
-            t.mutex.unlock();
+            mutexUnlock(&t.mutex);
             thread.cancel_protection = .unblocked;
             const runnable: *Runnable = @fieldParentPtr("node", runnable_node);
             runnable.startFn(runnable, &thread, t);
-            t.mutex.lock();
+            mutexLockUncancelable(&t.mutex);
             t.busy_count -= 1;
         }
         if (t.join_requested) break;
-        t.cond.wait(&t.mutex);
+        condWait(&t.cond, &t.mutex);
     }
 }
 
@@ -2004,12 +2004,12 @@ fn async(
         },
     };
 
-    t.mutex.lock();
+    mutexLockUncancelable(&t.mutex);
 
     const busy_count = t.busy_count;
 
     if (busy_count >= @intFromEnum(t.async_limit)) {
-        t.mutex.unlock();
+        mutexUnlock(&t.mutex);
         future.destroy(gpa);
         start(context.ptr, result.ptr);
         return null;
@@ -2023,7 +2023,7 @@ fn async(
         const thread = std.Thread.spawn(.{ .stack_size = t.stack_size }, worker, .{t}) catch {
             t.wait_group.finish();
             t.busy_count = busy_count;
-            t.mutex.unlock();
+            mutexUnlock(&t.mutex);
             future.destroy(gpa);
             start(context.ptr, result.ptr);
             return null;
@@ -2033,8 +2033,8 @@ fn async(
 
     t.run_queue.prepend(&future.runnable.node);
 
-    t.mutex.unlock();
-    t.cond.signal();
+    mutexUnlock(&t.mutex);
+    condSignal(&t.cond);
     return @ptrCast(future);
 }
 
@@ -2056,8 +2056,8 @@ fn concurrent(
     };
     errdefer future.destroy(gpa);
 
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
 
     const busy_count = t.busy_count;
 
@@ -2080,7 +2080,7 @@ fn concurrent(
 
     t.run_queue.prepend(&future.runnable.node);
 
-    t.cond.signal();
+    condSignal(&t.cond);
     return @ptrCast(future);
 }
 
@@ -2101,12 +2101,12 @@ fn groupAsync(
         error.OutOfMemory => return groupAsyncEager(start, context.ptr),
     };
 
-    t.mutex.lock();
+    mutexLockUncancelable(&t.mutex);
 
     const busy_count = t.busy_count;
 
     if (busy_count >= @intFromEnum(t.async_limit)) {
-        t.mutex.unlock();
+        mutexUnlock(&t.mutex);
         task.destroy(gpa);
         return groupAsyncEager(start, context.ptr);
     }
@@ -2119,7 +2119,7 @@ fn groupAsync(
         const thread = std.Thread.spawn(.{ .stack_size = t.stack_size }, worker, .{t}) catch {
             t.wait_group.finish();
             t.busy_count = busy_count;
-            t.mutex.unlock();
+            mutexUnlock(&t.mutex);
             task.destroy(gpa);
             return groupAsyncEager(start, context.ptr);
         };
@@ -2136,8 +2136,8 @@ fn groupAsync(
     }, .monotonic);
     t.run_queue.prepend(&task.runnable.node);
 
-    t.mutex.unlock();
-    t.cond.signal();
+    mutexUnlock(&t.mutex);
+    condSignal(&t.cond);
 }
 fn groupAsyncEager(
     start: *const fn (context: *const anyopaque) Io.Cancelable!void,
@@ -2201,8 +2201,8 @@ fn groupConcurrent(
     };
     errdefer task.destroy(gpa);
 
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
 
     const busy_count = t.busy_count;
 
@@ -2233,7 +2233,7 @@ fn groupConcurrent(
     }, .monotonic);
     t.run_queue.prepend(&task.runnable.node);
 
-    t.cond.signal();
+    condSignal(&t.cond);
 }
 
 fn groupAwait(userdata: ?*anyopaque, type_erased: *Io.Group, initial_token: *anyopaque) Io.Cancelable!void {
@@ -3838,8 +3838,8 @@ fn fileStatWindows(userdata: ?*anyopaque, file: File) File.StatError!File.Stat {
 
 fn systemBasicInformation(t: *Threaded) ?*const windows.SYSTEM_BASIC_INFORMATION {
     if (!t.system_basic_information.initialized.load(.acquire)) {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
 
         switch (windows.ntdll.NtQuerySystemInformation(
             .SystemBasicInformation,
@@ -14373,8 +14373,8 @@ const WindowsEnvironStrings = struct {
 };
 
 fn scanEnviron(t: *Threaded) void {
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
 
     if (t.environ.initialized) return;
     t.environ.initialized = true;
@@ -14729,8 +14729,8 @@ fn spawnPosix(t: *Threaded, options: process.SpawnOptions) process.SpawnError!Sp
 
 fn getDevNullFd(t: *Threaded) !posix.fd_t {
     {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
         if (t.null_file.fd != -1) return t.null_file.fd;
     }
     const mode: u32 = 0;
@@ -14741,8 +14741,8 @@ fn getDevNullFd(t: *Threaded) !posix.fd_t {
             .SUCCESS => {
                 syscall.finish();
                 const fresh_fd: posix.fd_t = @intCast(rc);
-                t.mutex.lock(); // Another thread might have won the race.
-                defer t.mutex.unlock();
+                mutexLockUncancelable(&t.mutex); // Another thread might have won the race.
+                defer mutexUnlock(&t.mutex);
                 if (t.null_file.fd != -1) {
                     posix.close(fresh_fd);
                     return t.null_file.fd;
@@ -15402,8 +15402,8 @@ fn processSpawnWindows(userdata: ?*anyopaque, options: process.SpawnOptions) pro
 
 fn getCngHandle(t: *Threaded) Io.RandomSecureError!windows.HANDLE {
     {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
         if (t.random_file.handle) |handle| return handle;
     }
 
@@ -15437,8 +15437,8 @@ fn getCngHandle(t: *Threaded) Io.RandomSecureError!windows.HANDLE {
     )) {
         .SUCCESS => {
             syscall.finish();
-            t.mutex.lock(); // Another thread might have won the race.
-            defer t.mutex.unlock();
+            mutexLockUncancelable(&t.mutex); // Another thread might have won the race.
+            defer mutexUnlock(&t.mutex);
             if (t.random_file.handle) |prev_handle| {
                 windows.CloseHandle(fresh_handle);
                 return prev_handle;
@@ -15458,8 +15458,8 @@ fn getCngHandle(t: *Threaded) Io.RandomSecureError!windows.HANDLE {
 
 fn getNulHandle(t: *Threaded) !windows.HANDLE {
     {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
         if (t.null_file.handle) |handle| return handle;
     }
 
@@ -15505,8 +15505,8 @@ fn getNulHandle(t: *Threaded) !windows.HANDLE {
     )) {
         .SUCCESS => {
             syscall.finish();
-            t.mutex.lock(); // Another thread might have won the race.
-            defer t.mutex.unlock();
+            mutexLockUncancelable(&t.mutex); // Another thread might have won the race.
+            defer mutexUnlock(&t.mutex);
             if (t.null_file.handle) |prev_handle| {
                 windows.CloseHandle(fresh_handle);
                 return prev_handle;
@@ -16551,15 +16551,15 @@ fn random(userdata: ?*anyopaque, buffer: []u8) void {
 }
 
 fn randomMainThread(t: *Threaded, buffer: []u8) void {
-    t.mutex.lock();
-    defer t.mutex.unlock();
+    mutexLockUncancelable(&t.mutex);
+    defer mutexUnlock(&t.mutex);
 
     if (!t.csprng.isInitialized()) {
         @branchHint(.unlikely);
         var seed: [Csprng.seed_len]u8 = undefined;
         {
-            t.mutex.unlock();
-            defer t.mutex.lock();
+            mutexUnlock(&t.mutex);
+            defer mutexLockUncancelable(&t.mutex);
 
             const prev = swapCancelProtection(t, .blocked);
             defer _ = swapCancelProtection(t, prev);
@@ -16744,8 +16744,8 @@ fn randomSecure(userdata: ?*anyopaque, buffer: []u8) Io.RandomSecureError!void {
 
 fn getRandomFd(t: *Threaded) Io.RandomSecureError!posix.fd_t {
     {
-        t.mutex.lock();
-        defer t.mutex.unlock();
+        mutexLockUncancelable(&t.mutex);
+        defer mutexUnlock(&t.mutex);
 
         if (t.random_file.fd == -2) return error.EntropyUnavailable;
         if (t.random_file.fd != -1) return t.random_file.fd;
@@ -16785,8 +16785,8 @@ fn getRandomFd(t: *Threaded) Io.RandomSecureError!posix.fd_t {
                     .SUCCESS => {
                         syscall.finish();
                         if (!statx.mask.TYPE) return error.EntropyUnavailable;
-                        t.mutex.lock(); // Another thread might have won the race.
-                        defer t.mutex.unlock();
+                        mutexLockUncancelable(&t.mutex); // Another thread might have won the race.
+                        defer mutexUnlock(&t.mutex);
                         if (t.random_file.fd >= 0) {
                             posix.close(fd);
                             return t.random_file.fd;
@@ -16813,8 +16813,8 @@ fn getRandomFd(t: *Threaded) Io.RandomSecureError!posix.fd_t {
                 switch (posix.errno(fstat_sym(fd, &stat))) {
                     .SUCCESS => {
                         syscall.finish();
-                        t.mutex.lock(); // Another thread might have won the race.
-                        defer t.mutex.unlock();
+                        mutexLockUncancelable(&t.mutex); // Another thread might have won the race.
+                        defer mutexUnlock(&t.mutex);
                         if (t.random_file.fd >= 0) {
                             posix.close(fd);
                             return t.random_file.fd;
@@ -16878,13 +16878,13 @@ const parking_futex = struct {
         /// avoid a race.
         num_waiters: std.atomic.Value(u32),
         /// Protects `waiters`.
-        mutex: std.Thread.Mutex,
+        mutex: Mutex,
         waiters: std.DoublyLinkedList,
 
         /// Prevent false sharing between buckets.
         _: void align(std.atomic.cache_line) = {},
 
-        const init: Bucket = .{ .num_waiters = .init(0), .mutex = .{}, .waiters = .{} };
+        const init: Bucket = .{ .num_waiters = .init(0), .mutex = .init, .waiters = .{} };
     };
 
     const Waiter = struct {
@@ -16947,8 +16947,8 @@ const parking_futex = struct {
         var status_buf: std.atomic.Value(Thread.Status) = undefined;
 
         {
-            bucket.mutex.lock();
-            defer bucket.mutex.unlock();
+            mutexLockUncancelable(&bucket.mutex);
+            defer mutexUnlock(&bucket.mutex);
 
             _ = bucket.num_waiters.fetchAdd(1, .acquire);
 
@@ -17017,8 +17017,8 @@ const parking_futex = struct {
                 .parked => {
                     // We saw a timeout and updated our own status from `.parked` to `.none`. It is
                     // our responsibility to remove `waiter` from `bucket`.
-                    bucket.mutex.lock();
-                    defer bucket.mutex.unlock();
+                    mutexLockUncancelable(&bucket.mutex);
+                    defer mutexUnlock(&bucket.mutex);
                     bucket.waiters.remove(&waiter.node);
                     assert(bucket.num_waiters.fetchSub(1, .monotonic) > 0);
                 },
@@ -17057,8 +17057,8 @@ const parking_futex = struct {
         // of the critical section. This forms a singly-linked list of waiters using `Waiter.node.next`.
         var waking_head: ?*std.DoublyLinkedList.Node = null;
         {
-            bucket.mutex.lock();
-            defer bucket.mutex.unlock();
+            mutexLockUncancelable(&bucket.mutex);
+            defer mutexUnlock(&bucket.mutex);
 
             var num_removed: u32 = 0;
             var it = bucket.waiters.first;
@@ -17113,8 +17113,8 @@ const parking_futex = struct {
 
     fn removeCanceledWaiter(waiter: *Waiter) void {
         const bucket = bucketForAddress(waiter.address);
-        bucket.mutex.lock();
-        defer bucket.mutex.unlock();
+        mutexLockUncancelable(&bucket.mutex);
+        defer mutexUnlock(&bucket.mutex);
         bucket.waiters.remove(&waiter.node);
         assert(bucket.num_waiters.fetchSub(1, .monotonic) > 0);
         waiter.done.store(true, .release); // potentially invalidates `waiter.*`
@@ -18102,3 +18102,141 @@ fn eventSet(event: *Io.Event) void {
         .waiting => Thread.futexWake(@ptrCast(event), std.math.maxInt(u32)),
     }
 }
+
+const Condition = if (!is_windows) Io.Condition else struct {
+    condition: windows.CONDITION_VARIABLE,
+    const init: @This() = .{ .condition = .{} };
+};
+
+/// Same as `Io.Condition.broadcast` but avoids the VTable.
+fn condBroadcast(cond: *Condition) void {
+    if (is_windows) return windows.ntdll.RtlWakeAllConditionVariable(&cond.condition);
+    var prev_state = cond.state.load(.monotonic);
+    while (prev_state.waiters > prev_state.signals) {
+        @branchHint(.unlikely);
+        prev_state = cond.state.cmpxchgWeak(prev_state, .{
+            .waiters = prev_state.waiters,
+            .signals = prev_state.waiters,
+        }, .release, .monotonic) orelse {
+            // Update the epoch to tell the waiting threads that there are new signals for them.
+            // Note that a waiting thread could miss a take if *exactly* (1<<32)-1 wakes happen
+            // between it observing the epoch and sleeping on it, but this is extraordinarily
+            // unlikely due to the precise number of calls required.
+            _ = cond.epoch.fetchAdd(1, .release); // `.release` to ensure ordered after `state` update
+            Thread.futexWake(&cond.epoch.raw, prev_state.waiters - prev_state.signals);
+            return;
+        };
+    }
+}
+
+/// Same as `Io.Condition.signal` but avoids the VTable.
+fn condSignal(cond: *Condition) void {
+    if (is_windows) return windows.ntdll.RtlWakeConditionVariable(&cond.condition);
+    var prev_state = cond.state.load(.monotonic);
+    while (prev_state.waiters > prev_state.signals) {
+        @branchHint(.unlikely);
+        prev_state = cond.state.cmpxchgWeak(prev_state, .{
+            .waiters = prev_state.waiters,
+            .signals = prev_state.signals + 1,
+        }, .release, .monotonic) orelse {
+            // Update the epoch to tell the waiting threads that there are new signals for them.
+            // Note that a waiting thread could miss a take if *exactly* (1<<32)-1 wakes happen
+            // between it observing the epoch and sleeping on it, but this is extraordinarily
+            // unlikely due to the precise number of calls required.
+            _ = cond.epoch.fetchAdd(1, .release); // `.release` to ensure ordered after `state` update
+            Thread.futexWake(&cond.epoch.raw, 1);
+            return;
+        };
+    }
+}
+
+/// Same as `Io.Condition.waitUncancelable` but avoids the VTable.
+fn condWait(cond: *Condition, mutex: *Mutex) void {
+    if (is_windows) {
+        _ = windows.kernel32.SleepConditionVariableSRW(&cond.condition, &mutex.srwlock, windows.INFINITE, 0);
+        return;
+    }
+    var epoch = cond.epoch.load(.acquire); // `.acquire` to ensure ordered before state load
+
+    {
+        const prev_state = cond.state.fetchAdd(.{ .waiters = 1, .signals = 0 }, .monotonic);
+        assert(prev_state.waiters < std.math.maxInt(u16)); // overflow caused by too many waiters
+    }
+
+    mutexUnlock(mutex);
+    defer mutexLockUncancelable(mutex);
+
+    while (true) {
+        Thread.futexWaitUncancelable(&cond.epoch.raw, epoch, null);
+
+        epoch = cond.epoch.load(.acquire); // `.acquire` to ensure ordered before `state` laod
+
+        var prev_state = cond.state.load(.monotonic);
+        while (prev_state.signals > 0) {
+            prev_state = cond.state.cmpxchgWeak(prev_state, .{
+                .waiters = prev_state.waiters - 1,
+                .signals = prev_state.signals - 1,
+            }, .acquire, .monotonic) orelse {
+                // We successfully consumed a signal.
+                return;
+            };
+        }
+    }
+}
+
+const Mutex = if (!is_windows) Io.Mutex else struct {
+    srwlock: windows.SRWLOCK,
+    const init: @This() = .{ .srwlock = .{} };
+};
+
+/// Same as `Io.Mutex.lockUncancelable` but avoids the VTable.
+fn mutexLock(m: *Io.Mutex) Io.Cancelable!void {
+    const initial_state = m.state.cmpxchgWeak(
+        .unlocked,
+        .locked_once,
+        .acquire,
+        .monotonic,
+    ) orelse {
+        @branchHint(.likely);
+        return;
+    };
+    if (initial_state == .contended) {
+        try Thread.futexWait(@ptrCast(&m.state.raw), @intFromEnum(Io.Mutex.State.contended), null);
+    }
+    while (m.state.swap(.contended, .acquire) != .unlocked) {
+        try Thread.futexWait(@ptrCast(&m.state.raw), @intFromEnum(Io.Mutex.State.contended), null);
+    }
+}
+
+/// Same as `Io.Mutex.lockUncancelable` but avoids the VTable.
+fn mutexLockUncancelable(m: *Mutex) void {
+    if (is_windows) return windows.ntdll.RtlAcquireSRWLockExclusive(&m.srwlock);
+    const initial_state = m.state.cmpxchgWeak(
+        .unlocked,
+        .locked_once,
+        .acquire,
+        .monotonic,
+    ) orelse {
+        @branchHint(.likely);
+        return;
+    };
+    if (initial_state == .contended) {
+        Thread.futexWaitUncancelable(@ptrCast(&m.state.raw), @intFromEnum(Io.Mutex.State.contended), null);
+    }
+    while (m.state.swap(.contended, .acquire) != .unlocked) {
+        Thread.futexWaitUncancelable(@ptrCast(&m.state.raw), @intFromEnum(Io.Mutex.State.contended), null);
+    }
+}
+
+/// Same as `Io.Mutex.unlock` but avoids the VTable.
+fn mutexUnlock(m: *Mutex) void {
+    if (is_windows) return windows.ntdll.RtlReleaseSRWLockExclusive(&m.srwlock);
+    switch (m.state.swap(.unlocked, .release)) {
+        .unlocked => unreachable,
+        .locked_once => {},
+        .contended => {
+            @branchHint(.unlikely);
+            Thread.futexWake(@ptrCast(&m.state.raw), 1);
+        },
+    }
+}