From 9e62075db8e6094e840a2572d443880e3a4c1060 Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Wed, 15 Feb 2023 15:10:09 -0800
Subject: [PATCH 1/6] Add a fallback when threading is unsupported

---
 rayon-core/src/lib.rs      |  4 ++
 rayon-core/src/registry.rs | 76 +++++++++++++++++++++++++++++---------
 2 files changed, 63 insertions(+), 17 deletions(-)

diff --git a/rayon-core/src/lib.rs b/rayon-core/src/lib.rs
index b31a2d7e0..d0d2ea406 100644
--- a/rayon-core/src/lib.rs
+++ b/rayon-core/src/lib.rs
@@ -707,6 +707,10 @@ impl ThreadPoolBuildError {
     fn new(kind: ErrorKind) -> ThreadPoolBuildError {
         ThreadPoolBuildError { kind }
     }
+
+    fn is_unsupported(&self) -> bool {
+        matches!(&self.kind, ErrorKind::IOError(e) if e.kind() == io::ErrorKind::Unsupported)
+    }
 }
 
 const GLOBAL_POOL_ALREADY_INITIALIZED: &str =
diff --git a/rayon-core/src/registry.rs b/rayon-core/src/registry.rs
index 24c0855c6..cd021230f 100644
--- a/rayon-core/src/registry.rs
+++ b/rayon-core/src/registry.rs
@@ -50,7 +50,7 @@ impl ThreadBuilder {
     /// Executes the main loop for this thread. This will not return until the
     /// thread pool is dropped.
     pub fn run(self) {
-        unsafe { main_loop(self.worker, self.stealer, self.registry, self.index) }
+        unsafe { main_loop(self) }
     }
 }
 
@@ -164,7 +164,7 @@ static THE_REGISTRY_SET: Once = Once::new();
 /// initialization has not already occurred, use the default
 /// configuration.
 pub(super) fn global_registry() -> &'static Arc<Registry> {
-    set_global_registry(|| Registry::new(ThreadPoolBuilder::new()))
+    set_global_registry(default_global_registry)
         .or_else(|err| unsafe { THE_REGISTRY.as_ref().ok_or(err) })
         .expect("The global thread pool has not been initialized.")
 }
@@ -198,6 +198,46 @@ where
     result
 }
 
+fn default_global_registry() -> Result<Arc<Registry>, ThreadPoolBuildError> {
+    let result = Registry::new(ThreadPoolBuilder::new());
+
+    // If we're running in an environment that doesn't support threads at all, we can fall back to
+    // using the current thread alone. This is crude, and probably won't work for non-blocking
+    // calls like `spawn` or `broadcast_spawn`, but a lot of stuff does work fine.
+    //
+    // Notably, this allows current WebAssembly targets to work even though their threading support
+    // is stubbed out, and we won't have to change anything if they do add real threading.
+    let unsupported = matches!(&result, Err(e) if e.is_unsupported());
+    if unsupported && WorkerThread::current().is_null() {
+        let builder = ThreadPoolBuilder::new()
+            .num_threads(1)
+            .spawn_handler(|thread| {
+                // Rather than starting a new thread, we're just taking over the current thread
+                // *without* running the main loop, so we can still return from here.
+                // The WorkerThread is leaked, but we never shutdown the global pool anyway.
+                let worker_thread = Box::leak(Box::new(WorkerThread::from(thread)));
+                let registry = &*worker_thread.registry;
+                let index = worker_thread.index;
+
+                unsafe {
+                    WorkerThread::set_current(worker_thread);
+
+                    // let registry know we are ready to do work
+                    Latch::set(&registry.thread_infos[index].primed);
+                }
+
+                Ok(())
+            });
+
+        let fallback_result = Registry::new(builder);
+        if fallback_result.is_ok() {
+            return fallback_result;
+        }
+    }
+
+    result
+}
+
 struct Terminator<'a>(&'a Arc<Registry>);
 
 impl<'a> Drop for Terminator<'a> {
@@ -655,6 +695,19 @@ thread_local! {
     static WORKER_THREAD_STATE: Cell<*const WorkerThread> = Cell::new(ptr::null());
 }
 
+impl From<ThreadBuilder> for WorkerThread {
+    fn from(thread: ThreadBuilder) -> Self {
+        Self {
+            worker: thread.worker,
+            stealer: thread.stealer,
+            fifo: JobFifo::new(),
+            index: thread.index,
+            rng: XorShift64Star::new(),
+            registry: thread.registry,
+        }
+    }
+}
+
 impl Drop for WorkerThread {
     fn drop(&mut self) {
         // Undo `set_current`
@@ -851,22 +904,11 @@ impl WorkerThread {
 
 /// ////////////////////////////////////////////////////////////////////////
 
-unsafe fn main_loop(
-    worker: Worker<JobRef>,
-    stealer: Stealer<JobRef>,
-    registry: Arc<Registry>,
-    index: usize,
-) {
-    let worker_thread = &WorkerThread {
-        worker,
-        stealer,
-        fifo: JobFifo::new(),
-        index,
-        rng: XorShift64Star::new(),
-        registry,
-    };
+unsafe fn main_loop(thread: ThreadBuilder) {
+    let worker_thread = &WorkerThread::from(thread);
     WorkerThread::set_current(worker_thread);
     let registry = &*worker_thread.registry;
+    let index = worker_thread.index;
 
     // let registry know we are ready to do work
     Latch::set(&registry.thread_infos[index].primed);
@@ -924,7 +966,7 @@ where
             // invalidated until we return.
             op(&*owner_thread, false)
         } else {
-            global_registry().in_worker_cold(op)
+            global_registry().in_worker(op)
         }
     }
 }

From 289883035dff786622cb828766a16ae02eb083f0 Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Fri, 17 Feb 2023 10:54:01 -0800
Subject: [PATCH 2/6] Filter tests that need panic unwinding

---
 rayon-core/src/broadcast/test.rs   | 4 ++++
 rayon-core/src/join/test.rs        | 1 +
 rayon-core/src/scope/test.rs       | 4 ++++
 rayon-core/src/spawn/test.rs       | 3 +++
 rayon-core/src/thread_pool/test.rs | 1 +
 src/iter/collect/test.rs           | 2 ++
 tests/collect.rs                   | 2 ++
 tests/iter_panic.rs                | 1 +
 8 files changed, 18 insertions(+)

diff --git a/rayon-core/src/broadcast/test.rs b/rayon-core/src/broadcast/test.rs
index a765cb034..eb4754c32 100644
--- a/rayon-core/src/broadcast/test.rs
+++ b/rayon-core/src/broadcast/test.rs
@@ -130,6 +130,7 @@ fn spawn_broadcast_mutual_sleepy() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn broadcast_panic_one() {
     let count = AtomicUsize::new(0);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -146,6 +147,7 @@ fn broadcast_panic_one() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn spawn_broadcast_panic_one() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let (panic_tx, panic_rx) = crossbeam_channel::unbounded();
@@ -166,6 +168,7 @@ fn spawn_broadcast_panic_one() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn broadcast_panic_many() {
     let count = AtomicUsize::new(0);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -182,6 +185,7 @@ fn broadcast_panic_many() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn spawn_broadcast_panic_many() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let (panic_tx, panic_rx) = crossbeam_channel::unbounded();
diff --git a/rayon-core/src/join/test.rs b/rayon-core/src/join/test.rs
index e7f287f6f..e01378b92 100644
--- a/rayon-core/src/join/test.rs
+++ b/rayon-core/src/join/test.rs
@@ -77,6 +77,7 @@ fn panic_propagate_both() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_b_still_executes() {
     let mut x = false;
     match unwind::halt_unwinding(|| join(|| panic!("Hello, world!"), || x = true)) {
diff --git a/rayon-core/src/scope/test.rs b/rayon-core/src/scope/test.rs
index 00dd18c92..5d4fa7a12 100644
--- a/rayon-core/src/scope/test.rs
+++ b/rayon-core/src/scope/test.rs
@@ -213,6 +213,7 @@ fn panic_propagate_nested_scope_spawn() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_propagate_still_execute_1() {
     let mut x = false;
     match unwind::halt_unwinding(|| {
@@ -227,6 +228,7 @@ fn panic_propagate_still_execute_1() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_propagate_still_execute_2() {
     let mut x = false;
     match unwind::halt_unwinding(|| {
@@ -241,6 +243,7 @@ fn panic_propagate_still_execute_2() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_propagate_still_execute_3() {
     let mut x = false;
     match unwind::halt_unwinding(|| {
@@ -255,6 +258,7 @@ fn panic_propagate_still_execute_3() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_propagate_still_execute_4() {
     let mut x = false;
     match unwind::halt_unwinding(|| {
diff --git a/rayon-core/src/spawn/test.rs b/rayon-core/src/spawn/test.rs
index 761fafc77..8c453a0db 100644
--- a/rayon-core/src/spawn/test.rs
+++ b/rayon-core/src/spawn/test.rs
@@ -23,6 +23,7 @@ fn spawn_then_join_outside_worker() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_fwd() {
     let (tx, rx) = channel();
 
@@ -80,6 +81,7 @@ fn termination_while_things_are_executing() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn custom_panic_handler_and_spawn() {
     let (tx, rx) = channel();
 
@@ -107,6 +109,7 @@ fn custom_panic_handler_and_spawn() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn custom_panic_handler_and_nested_spawn() {
     let (tx, rx) = channel();
 
diff --git a/rayon-core/src/thread_pool/test.rs b/rayon-core/src/thread_pool/test.rs
index ac750a6dc..142ba6b79 100644
--- a/rayon-core/src/thread_pool/test.rs
+++ b/rayon-core/src/thread_pool/test.rs
@@ -115,6 +115,7 @@ fn failed_thread_stack() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn panic_thread_name() {
     let (start_count, start_handler) = count_handler();
     let (exit_count, exit_handler) = count_handler();
diff --git a/src/iter/collect/test.rs b/src/iter/collect/test.rs
index b5f676f5d..97bec3f4e 100644
--- a/src/iter/collect/test.rs
+++ b/src/iter/collect/test.rs
@@ -76,6 +76,7 @@ fn right_produces_items_with_no_complete() {
 
 // Complete is not called by the consumer. Hence,the collection vector is not fully initialized.
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn produces_items_with_no_complete() {
     let counter = DropCounter::default();
     let mut v = vec![];
@@ -273,6 +274,7 @@ fn right_panics() {
 // The left consumer produces fewer items while the right
 // consumer produces correct number; check that created elements are dropped
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn left_produces_fewer_items_drops() {
     let counter = DropCounter::default();
     let mut v = vec![];
diff --git a/tests/collect.rs b/tests/collect.rs
index 48b80f699..bfb080ceb 100644
--- a/tests/collect.rs
+++ b/tests/collect.rs
@@ -6,6 +6,7 @@ use std::sync::atomic::Ordering;
 use std::sync::Mutex;
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn collect_drop_on_unwind() {
     struct Recorddrop<'a>(i64, &'a Mutex<Vec<i64>>);
 
@@ -61,6 +62,7 @@ fn collect_drop_on_unwind() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn collect_drop_on_unwind_zst() {
     static INSERTS: AtomicUsize = AtomicUsize::new(0);
     static DROPS: AtomicUsize = AtomicUsize::new(0);
diff --git a/tests/iter_panic.rs b/tests/iter_panic.rs
index 37d4d6a3a..c62a8dbda 100644
--- a/tests/iter_panic.rs
+++ b/tests/iter_panic.rs
@@ -20,6 +20,7 @@ fn iter_panic() {
 }
 
 #[test]
+#[cfg_attr(not(panic = "unwind"), ignore)]
 fn iter_panic_fuse() {
     // We only use a single thread in order to make the behavior
     // of 'panic_fuse' deterministic

From ae79f0e62e954082214ae0c4bce04b39b2bffd53 Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Fri, 17 Feb 2023 10:55:21 -0800
Subject: [PATCH 3/6] Filter tests that need true threading

---
 rayon-core/src/broadcast/test.rs         | 10 ++++++++
 rayon-core/src/join/test.rs              |  5 ++++
 rayon-core/src/scope/test.rs             | 14 +++++++++++
 rayon-core/src/spawn/test.rs             |  9 +++++++
 rayon-core/src/test.rs                   |  8 ++++++
 rayon-core/src/thread_pool/test.rs       | 15 +++++++++++
 rayon-core/tests/double_init_fail.rs     |  1 +
 rayon-core/tests/init_zero_threads.rs    |  1 +
 rayon-core/tests/scoped_threadpool.rs    |  3 +++
 rayon-core/tests/stack_overflow_crash.rs |  2 ++
 src/iter/test.rs                         |  3 +++
 tests/cross-pool.rs                      |  1 +
 tests/named-threads.rs                   |  1 +
 tests/octillion.rs                       | 32 +++++++++++++++++++++---
 tests/par_bridge_recursion.rs            |  1 +
 tests/sort-panic-safe.rs                 |  1 +
 16 files changed, 104 insertions(+), 3 deletions(-)

diff --git a/rayon-core/src/broadcast/test.rs b/rayon-core/src/broadcast/test.rs
index eb4754c32..a2b3acdd8 100644
--- a/rayon-core/src/broadcast/test.rs
+++ b/rayon-core/src/broadcast/test.rs
@@ -12,6 +12,7 @@ fn broadcast_global() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_broadcast_global() {
     let (tx, rx) = crossbeam_channel::unbounded();
     crate::spawn_broadcast(move |ctx| tx.send(ctx.index()).unwrap());
@@ -22,6 +23,7 @@ fn spawn_broadcast_global() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn broadcast_pool() {
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
     let v = pool.broadcast(|ctx| ctx.index());
@@ -29,6 +31,7 @@ fn broadcast_pool() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_broadcast_pool() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -40,6 +43,7 @@ fn spawn_broadcast_pool() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn broadcast_self() {
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
     let v = pool.install(|| crate::broadcast(|ctx| ctx.index()));
@@ -47,6 +51,7 @@ fn broadcast_self() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_broadcast_self() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -58,6 +63,7 @@ fn spawn_broadcast_self() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn broadcast_mutual() {
     let count = AtomicUsize::new(0);
     let pool1 = ThreadPoolBuilder::new().num_threads(3).build().unwrap();
@@ -73,6 +79,7 @@ fn broadcast_mutual() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_broadcast_mutual() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let pool1 = Arc::new(ThreadPoolBuilder::new().num_threads(3).build().unwrap());
@@ -90,6 +97,7 @@ fn spawn_broadcast_mutual() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn broadcast_mutual_sleepy() {
     let count = AtomicUsize::new(0);
     let pool1 = ThreadPoolBuilder::new().num_threads(3).build().unwrap();
@@ -108,6 +116,7 @@ fn broadcast_mutual_sleepy() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_broadcast_mutual_sleepy() {
     let (tx, rx) = crossbeam_channel::unbounded();
     let pool1 = Arc::new(ThreadPoolBuilder::new().num_threads(3).build().unwrap());
@@ -206,6 +215,7 @@ fn spawn_broadcast_panic_many() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn broadcast_sleep_race() {
     let test_duration = time::Duration::from_secs(1);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
diff --git a/rayon-core/src/join/test.rs b/rayon-core/src/join/test.rs
index e01378b92..b303dbc81 100644
--- a/rayon-core/src/join/test.rs
+++ b/rayon-core/src/join/test.rs
@@ -47,6 +47,7 @@ fn sort() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn sort_in_pool() {
     let rng = seeded_rng();
     let mut data: Vec<u32> = rng.sample_iter(&Standard).take(12 * 1024).collect();
@@ -87,6 +88,7 @@ fn panic_b_still_executes() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn join_context_both() {
     // If we're not in a pool, both should be marked stolen as they're injected.
     let (a_migrated, b_migrated) = join_context(|a| a.migrated(), |b| b.migrated());
@@ -95,6 +97,7 @@ fn join_context_both() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn join_context_neither() {
     // If we're already in a 1-thread pool, neither job should be stolen.
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
@@ -105,6 +108,7 @@ fn join_context_neither() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn join_context_second() {
     use std::sync::Barrier;
 
@@ -128,6 +132,7 @@ fn join_context_second() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn join_counter_overflow() {
     const MAX: u32 = 500_000;
 
diff --git a/rayon-core/src/scope/test.rs b/rayon-core/src/scope/test.rs
index 5d4fa7a12..ad8c4af0b 100644
--- a/rayon-core/src/scope/test.rs
+++ b/rayon-core/src/scope/test.rs
@@ -148,6 +148,7 @@ fn update_tree() {
 /// linearly with N. We test this by some unsafe hackery and
 /// permitting an approx 10% change with a 10x input change.
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn linear_stack_growth() {
     let builder = ThreadPoolBuilder::new().num_threads(1);
     let pool = builder.build().unwrap();
@@ -296,6 +297,7 @@ macro_rules! test_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn lifo_order() {
     // In the absence of stealing, `scope()` runs its `spawn()` jobs in LIFO order.
     let vec = test_order!(scope => spawn);
@@ -304,6 +306,7 @@ fn lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn fifo_order() {
     // In the absence of stealing, `scope_fifo()` runs its `spawn_fifo()` jobs in FIFO order.
     let vec = test_order!(scope_fifo => spawn_fifo);
@@ -338,6 +341,7 @@ macro_rules! test_nested_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_lifo_order() {
     // In the absence of stealing, `scope()` runs its `spawn()` jobs in LIFO order.
     let vec = test_nested_order!(scope => spawn, scope => spawn);
@@ -346,6 +350,7 @@ fn nested_lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_fifo_order() {
     // In the absence of stealing, `scope_fifo()` runs its `spawn_fifo()` jobs in FIFO order.
     let vec = test_nested_order!(scope_fifo => spawn_fifo, scope_fifo => spawn_fifo);
@@ -354,6 +359,7 @@ fn nested_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_lifo_fifo_order() {
     // LIFO on the outside, FIFO on the inside
     let vec = test_nested_order!(scope => spawn, scope_fifo => spawn_fifo);
@@ -365,6 +371,7 @@ fn nested_lifo_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_fifo_lifo_order() {
     // FIFO on the outside, LIFO on the inside
     let vec = test_nested_order!(scope_fifo => spawn_fifo, scope => spawn);
@@ -407,6 +414,7 @@ macro_rules! test_mixed_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_lifo_order() {
     // NB: the end of the inner scope makes us execute some of the outer scope
     // before they've all been spawned, so they're not perfectly LIFO.
@@ -416,6 +424,7 @@ fn mixed_lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_fifo_order() {
     let vec = test_mixed_order!(scope_fifo => spawn_fifo, scope_fifo => spawn_fifo);
     let expected = vec![-1, 0, -2, 1, -3, 2, 3];
@@ -423,6 +432,7 @@ fn mixed_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_lifo_fifo_order() {
     // NB: the end of the inner scope makes us execute some of the outer scope
     // before they've all been spawned, so they're not perfectly LIFO.
@@ -432,6 +442,7 @@ fn mixed_lifo_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_fifo_lifo_order() {
     let vec = test_mixed_order!(scope_fifo => spawn_fifo, scope => spawn);
     let expected = vec![-3, 0, -2, 1, -1, 2, 3];
@@ -557,6 +568,7 @@ fn scope_spawn_broadcast_nested() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn scope_spawn_broadcast_barrier() {
     let barrier = Barrier::new(8);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -569,6 +581,7 @@ fn scope_spawn_broadcast_barrier() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn scope_spawn_broadcast_panic_one() {
     let count = AtomicUsize::new(0);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
@@ -587,6 +600,7 @@ fn scope_spawn_broadcast_panic_one() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn scope_spawn_broadcast_panic_many() {
     let count = AtomicUsize::new(0);
     let pool = ThreadPoolBuilder::new().num_threads(7).build().unwrap();
diff --git a/rayon-core/src/spawn/test.rs b/rayon-core/src/spawn/test.rs
index 8c453a0db..b7a0535aa 100644
--- a/rayon-core/src/spawn/test.rs
+++ b/rayon-core/src/spawn/test.rs
@@ -7,6 +7,7 @@ use super::{spawn, spawn_fifo};
 use crate::ThreadPoolBuilder;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_then_join_in_worker() {
     let (tx, rx) = channel();
     scope(move |_| {
@@ -16,6 +17,7 @@ fn spawn_then_join_in_worker() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_then_join_outside_worker() {
     let (tx, rx) = channel();
     spawn(move || tx.send(22).unwrap());
@@ -55,6 +57,7 @@ fn panic_fwd() {
 /// still active asynchronous tasks. We expect the thread-pool to stay
 /// alive and executing until those threads are complete.
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn termination_while_things_are_executing() {
     let (tx0, rx0) = channel();
     let (tx1, rx1) = channel();
@@ -168,6 +171,7 @@ macro_rules! test_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn lifo_order() {
     // In the absence of stealing, `spawn()` jobs on a thread will run in LIFO order.
     let vec = test_order!(spawn, spawn);
@@ -176,6 +180,7 @@ fn lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn fifo_order() {
     // In the absence of stealing, `spawn_fifo()` jobs on a thread will run in FIFO order.
     let vec = test_order!(spawn_fifo, spawn_fifo);
@@ -184,6 +189,7 @@ fn fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn lifo_fifo_order() {
     // LIFO on the outside, FIFO on the inside
     let vec = test_order!(spawn, spawn_fifo);
@@ -195,6 +201,7 @@ fn lifo_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn fifo_lifo_order() {
     // FIFO on the outside, LIFO on the inside
     let vec = test_order!(spawn_fifo, spawn);
@@ -232,6 +239,7 @@ macro_rules! test_mixed_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_lifo_fifo_order() {
     let vec = test_mixed_order!(spawn, spawn_fifo);
     let expected = vec![3, -1, 2, -2, 1, -3, 0];
@@ -239,6 +247,7 @@ fn mixed_lifo_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mixed_fifo_lifo_order() {
     let vec = test_mixed_order!(spawn_fifo, spawn);
     let expected = vec![0, -3, 1, -2, 2, -1, 3];
diff --git a/rayon-core/src/test.rs b/rayon-core/src/test.rs
index 46d63a7df..25b8487f7 100644
--- a/rayon-core/src/test.rs
+++ b/rayon-core/src/test.rs
@@ -5,6 +5,7 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::{Arc, Barrier};
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn worker_thread_index() {
     let pool = ThreadPoolBuilder::new().num_threads(22).build().unwrap();
     assert_eq!(pool.current_num_threads(), 22);
@@ -14,6 +15,7 @@ fn worker_thread_index() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn start_callback_called() {
     let n_threads = 16;
     let n_called = Arc::new(AtomicUsize::new(0));
@@ -40,6 +42,7 @@ fn start_callback_called() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn exit_callback_called() {
     let n_threads = 16;
     let n_called = Arc::new(AtomicUsize::new(0));
@@ -69,6 +72,7 @@ fn exit_callback_called() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn handler_panics_handled_correctly() {
     let n_threads = 16;
     let n_called = Arc::new(AtomicUsize::new(0));
@@ -119,6 +123,7 @@ fn handler_panics_handled_correctly() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn check_config_build() {
     let pool = ThreadPoolBuilder::new().num_threads(22).build().unwrap();
     assert_eq!(pool.current_num_threads(), 22);
@@ -134,6 +139,7 @@ fn check_error_send_sync() {
 
 #[allow(deprecated)]
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn configuration() {
     let start_handler = move |_| {};
     let exit_handler = move |_| {};
@@ -154,6 +160,7 @@ fn configuration() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn default_pool() {
     ThreadPoolBuilder::default().build().unwrap();
 }
@@ -162,6 +169,7 @@ fn default_pool() {
 /// the pool is done with them, allowing them to be used with rayon again
 /// later. e.g. WebAssembly want to have their own pool of available threads.
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn cleared_current_thread() -> Result<(), ThreadPoolBuildError> {
     let n_threads = 5;
     let mut handles = vec![];
diff --git a/rayon-core/src/thread_pool/test.rs b/rayon-core/src/thread_pool/test.rs
index 142ba6b79..aa9a4d31d 100644
--- a/rayon-core/src/thread_pool/test.rs
+++ b/rayon-core/src/thread_pool/test.rs
@@ -16,6 +16,7 @@ fn panic_propagate() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn workers_stop() {
     let registry;
 
@@ -43,6 +44,7 @@ fn join_a_lot(n: usize) {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn sleeper_stop() {
     use std::{thread, time};
 
@@ -89,6 +91,7 @@ fn wait_for_counter(mut counter: Arc<AtomicUsize>) -> usize {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn failed_thread_stack() {
     // Note: we first tried to force failure with a `usize::MAX` stack, but
     // macOS and Windows weren't fazed, or at least didn't fail the way we want.
@@ -140,6 +143,7 @@ fn panic_thread_name() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn self_install() {
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
 
@@ -148,6 +152,7 @@ fn self_install() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mutual_install() {
     let pool1 = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
     let pool2 = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
@@ -167,6 +172,7 @@ fn mutual_install() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn mutual_install_sleepy() {
     use std::{thread, time};
 
@@ -195,6 +201,7 @@ fn mutual_install_sleepy() {
 
 #[test]
 #[allow(deprecated)]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn check_thread_pool_new() {
     let pool = ThreadPool::new(crate::Configuration::new().num_threads(22)).unwrap();
     assert_eq!(pool.current_num_threads(), 22);
@@ -220,6 +227,7 @@ macro_rules! test_scope_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn scope_lifo_order() {
     let vec = test_scope_order!(scope => spawn);
     let expected: Vec<i32> = (0..10).rev().collect(); // LIFO -> reversed
@@ -227,6 +235,7 @@ fn scope_lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn scope_fifo_order() {
     let vec = test_scope_order!(scope_fifo => spawn_fifo);
     let expected: Vec<i32> = (0..10).collect(); // FIFO -> natural order
@@ -251,6 +260,7 @@ macro_rules! test_spawn_order {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_lifo_order() {
     let vec = test_spawn_order!(spawn);
     let expected: Vec<i32> = (0..10).rev().collect(); // LIFO -> reversed
@@ -258,6 +268,7 @@ fn spawn_lifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_fifo_order() {
     let vec = test_spawn_order!(spawn_fifo);
     let expected: Vec<i32> = (0..10).collect(); // FIFO -> natural order
@@ -265,6 +276,7 @@ fn spawn_fifo_order() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_scopes() {
     // Create matching scopes for every thread pool.
     fn nest<'scope, OP>(pools: &[ThreadPool], scopes: Vec<&Scope<'scope>>, op: OP)
@@ -301,6 +313,7 @@ fn nested_scopes() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn nested_fifo_scopes() {
     // Create matching fifo scopes for every thread pool.
     fn nest<'scope, OP>(pools: &[ThreadPool], scopes: Vec<&ScopeFifo<'scope>>, op: OP)
@@ -337,6 +350,7 @@ fn nested_fifo_scopes() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn in_place_scope_no_deadlock() {
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
     let (tx, rx) = channel();
@@ -352,6 +366,7 @@ fn in_place_scope_no_deadlock() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn in_place_scope_fifo_no_deadlock() {
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
     let (tx, rx) = channel();
diff --git a/rayon-core/tests/double_init_fail.rs b/rayon-core/tests/double_init_fail.rs
index b3ddbeb88..15915304d 100644
--- a/rayon-core/tests/double_init_fail.rs
+++ b/rayon-core/tests/double_init_fail.rs
@@ -2,6 +2,7 @@ use rayon_core::ThreadPoolBuilder;
 use std::error::Error;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn double_init_fail() {
     let result1 = ThreadPoolBuilder::new().build_global();
     assert!(result1.is_ok());
diff --git a/rayon-core/tests/init_zero_threads.rs b/rayon-core/tests/init_zero_threads.rs
index ebd73c585..3c1ad251c 100644
--- a/rayon-core/tests/init_zero_threads.rs
+++ b/rayon-core/tests/init_zero_threads.rs
@@ -1,6 +1,7 @@
 use rayon_core::ThreadPoolBuilder;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn init_zero_threads() {
     ThreadPoolBuilder::new()
         .num_threads(0)
diff --git a/rayon-core/tests/scoped_threadpool.rs b/rayon-core/tests/scoped_threadpool.rs
index db3d0b874..534e8bbf4 100644
--- a/rayon-core/tests/scoped_threadpool.rs
+++ b/rayon-core/tests/scoped_threadpool.rs
@@ -7,6 +7,7 @@ struct Local(i32);
 scoped_tls::scoped_thread_local!(static LOCAL: Local);
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn missing_scoped_tls() {
     LOCAL.set(&Local(42), || {
         let pool = ThreadPoolBuilder::new()
@@ -21,6 +22,7 @@ fn missing_scoped_tls() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn spawn_scoped_tls_threadpool() {
     LOCAL.set(&Local(42), || {
         LOCAL.with(|x| {
@@ -63,6 +65,7 @@ fn spawn_scoped_tls_threadpool() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn build_scoped_tls_threadpool() {
     LOCAL.set(&Local(42), || {
         LOCAL.with(|x| {
diff --git a/rayon-core/tests/stack_overflow_crash.rs b/rayon-core/tests/stack_overflow_crash.rs
index e87e151a9..7dcde43c4 100644
--- a/rayon-core/tests/stack_overflow_crash.rs
+++ b/rayon-core/tests/stack_overflow_crash.rs
@@ -40,10 +40,12 @@ fn overflow_code() -> Option<i32> {
 }
 
 #[test]
+#[cfg_attr(not(any(unix, windows)), ignore)]
 fn stack_overflow_crash() {
     // First check that the recursive call actually causes a stack overflow,
     // and does not get optimized away.
     let status = run_ignored("run_with_small_stack");
+    assert!(!status.success());
     #[cfg(any(unix, windows))]
     assert_eq!(status.code(), overflow_code());
     #[cfg(target_os = "linux")]
diff --git a/src/iter/test.rs b/src/iter/test.rs
index 94323d79d..c72068df7 100644
--- a/src/iter/test.rs
+++ b/src/iter/test.rs
@@ -468,6 +468,7 @@ fn check_cmp_gt_to_seq() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn check_cmp_short_circuit() {
     // We only use a single thread in order to make the short-circuit behavior deterministic.
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
@@ -497,6 +498,7 @@ fn check_cmp_short_circuit() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn check_partial_cmp_short_circuit() {
     // We only use a single thread to make the short-circuit behavior deterministic.
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
@@ -526,6 +528,7 @@ fn check_partial_cmp_short_circuit() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn check_partial_cmp_nan_short_circuit() {
     // We only use a single thread to make the short-circuit behavior deterministic.
     let pool = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
diff --git a/tests/cross-pool.rs b/tests/cross-pool.rs
index f0a2128a7..835e2e27f 100644
--- a/tests/cross-pool.rs
+++ b/tests/cross-pool.rs
@@ -2,6 +2,7 @@ use rayon::prelude::*;
 use rayon::ThreadPoolBuilder;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn cross_pool_busy() {
     let pool1 = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
     let pool2 = ThreadPoolBuilder::new().num_threads(1).build().unwrap();
diff --git a/tests/named-threads.rs b/tests/named-threads.rs
index fd1b0be2d..dadb37ba6 100644
--- a/tests/named-threads.rs
+++ b/tests/named-threads.rs
@@ -4,6 +4,7 @@ use rayon::prelude::*;
 use rayon::*;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn named_threads() {
     ThreadPoolBuilder::new()
         .thread_name(|i| format!("hello-name-test-{}", i))
diff --git a/tests/octillion.rs b/tests/octillion.rs
index cff2b1192..1af9ad8ba 100644
--- a/tests/octillion.rs
+++ b/tests/octillion.rs
@@ -68,7 +68,14 @@ fn two_threads<F: Send + FnOnce() -> R, R: Send>(f: F) -> R {
 }
 
 #[test]
-#[cfg_attr(not(target_pointer_width = "64"), ignore)]
+#[cfg_attr(
+    any(
+        not(target_pointer_width = "64"),
+        target_os = "emscripten",
+        target_family = "wasm"
+    ),
+    ignore
+)]
 fn find_last_octillion() {
     // It would be nice if `find_last` could prioritize the later splits,
     // basically flipping the `join` args, without needing indexed `rev`.
@@ -78,32 +85,49 @@ fn find_last_octillion() {
 }
 
 #[test]
-#[cfg_attr(not(target_pointer_width = "64"), ignore)]
+#[cfg_attr(
+    any(
+        not(target_pointer_width = "64"),
+        target_os = "emscripten",
+        target_family = "wasm"
+    ),
+    ignore
+)]
 fn find_last_octillion_inclusive() {
     let x = two_threads(|| octillion_inclusive().find_last(|_| true));
     assert_eq!(x, Some(OCTILLION));
 }
 
 #[test]
-#[cfg_attr(not(target_pointer_width = "64"), ignore)]
+#[cfg_attr(
+    any(
+        not(target_pointer_width = "64"),
+        target_os = "emscripten",
+        target_family = "wasm"
+    ),
+    ignore
+)]
 fn find_last_octillion_flat() {
     let x = two_threads(|| octillion_flat().find_last(|_| true));
     assert_eq!(x, Some(OCTILLION - 1));
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn find_any_octillion() {
     let x = two_threads(|| octillion().find_any(|x| *x > OCTILLION / 2));
     assert!(x.is_some());
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn find_any_octillion_flat() {
     let x = two_threads(|| octillion_flat().find_any(|x| *x > OCTILLION / 2));
     assert!(x.is_some());
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn filter_find_any_octillion() {
     let x = two_threads(|| {
         octillion()
@@ -114,6 +138,7 @@ fn filter_find_any_octillion() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn filter_find_any_octillion_flat() {
     let x = two_threads(|| {
         octillion_flat()
@@ -124,6 +149,7 @@ fn filter_find_any_octillion_flat() {
 }
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn fold_find_any_octillion_flat() {
     let x = two_threads(|| octillion_flat().fold(|| (), |_, _| ()).find_any(|_| true));
     assert!(x.is_some());
diff --git a/tests/par_bridge_recursion.rs b/tests/par_bridge_recursion.rs
index 4def0a9e4..3a48ef143 100644
--- a/tests/par_bridge_recursion.rs
+++ b/tests/par_bridge_recursion.rs
@@ -4,6 +4,7 @@ use std::iter::once_with;
 const N: usize = 100_000;
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn par_bridge_recursion() {
     let pool = rayon::ThreadPoolBuilder::new()
         .num_threads(10)
diff --git a/tests/sort-panic-safe.rs b/tests/sort-panic-safe.rs
index 00a973106..5d2be7d58 100644
--- a/tests/sort-panic-safe.rs
+++ b/tests/sort-panic-safe.rs
@@ -117,6 +117,7 @@ macro_rules! test {
 thread_local!(static SILENCE_PANIC: Cell<bool> = Cell::new(false));
 
 #[test]
+#[cfg_attr(any(target_os = "emscripten", target_family = "wasm"), ignore)]
 fn sort_panic_safe() {
     let prev = panic::take_hook();
     panic::set_hook(Box::new(move |info| {

From e3dd0a5f6dd57ffda9761b1dd5963b2b5c4156ff Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Fri, 17 Feb 2023 11:36:41 -0800
Subject: [PATCH 4/6] ci: test wasm32-wasi with wasmtime

---
 .github/workflows/ci.yaml | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index fe9b40694..23f2032a2 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -65,16 +65,24 @@ jobs:
       - run: cargo test --verbose --package rayon
       - run: cargo test --verbose --package rayon-core
 
-  # wasm won't actually work without threading, but it builds
+  # wasm32-unknown-unknown builds, and even has the runtime fallback for
+  # unsupported threading, but we don't have an environment to execute in.
+  # wasm32-wasi can test the fallback by running in wasmtime.
   wasm:
     name: WebAssembly
     runs-on: ubuntu-latest
+    env:
+      CARGO_TARGET_WASM32_WASI_RUNNER: /home/runner/.wasmtime/bin/wasmtime
     steps:
       - uses: actions/checkout@v3
       - uses: dtolnay/rust-toolchain@stable
         with:
-          target: wasm32-unknown-unknown
+          targets: wasm32-unknown-unknown,wasm32-wasi
       - run: cargo check --verbose --target wasm32-unknown-unknown
+      - run: cargo check --verbose --target wasm32-wasi
+      - run: curl https://wasmtime.dev/install.sh -sSf | bash
+      - run: cargo test --verbose --target wasm32-wasi --package rayon
+      - run: cargo test --verbose --target wasm32-wasi --package rayon-core
 
   fmt:
     name: Format

From 118a7445c610f1f1ddfb397a6b18cd31cb04d24e Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Tue, 21 Feb 2023 12:45:41 -0800
Subject: [PATCH 5/6] Add tests that broadcast does allow spawns to run

... even on "fallback" targets like `wasm32-wasi`!
---
 rayon-core/src/broadcast/test.rs | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/rayon-core/src/broadcast/test.rs b/rayon-core/src/broadcast/test.rs
index a2b3acdd8..3ae11f7f6 100644
--- a/rayon-core/src/broadcast/test.rs
+++ b/rayon-core/src/broadcast/test.rs
@@ -228,3 +228,35 @@ fn broadcast_sleep_race() {
         });
     }
 }
+
+#[test]
+fn broadcast_after_spawn_broadcast() {
+    let (tx, rx) = crossbeam_channel::unbounded();
+
+    // Queue a non-blocking spawn_broadcast.
+    crate::spawn_broadcast(move |ctx| tx.send(ctx.index()).unwrap());
+
+    // This blocking broadcast runs after all prior broadcasts.
+    crate::broadcast(|_| {});
+
+    // The spawn_broadcast **must** have run by now on all threads.
+    let mut v: Vec<_> = rx.try_iter().collect();
+    v.sort_unstable();
+    assert!(v.into_iter().eq(0..crate::current_num_threads()));
+}
+
+#[test]
+fn broadcast_after_spawn() {
+    let (tx, rx) = crossbeam_channel::bounded(1);
+
+    // Queue a regular spawn on a thread-local deque.
+    crate::registry::in_worker(move |_, _| {
+        crate::spawn(move || tx.send(22).unwrap());
+    });
+
+    // Broadcast runs after the local deque is empty.
+    crate::broadcast(|_| {});
+
+    // The spawn **must** have run by now.
+    assert_eq!(22, rx.try_recv().unwrap());
+}

From 26c249fbb0368a66ab9ca457e025e55e556fab0e Mon Sep 17 00:00:00 2001
From: Josh Stone <cuviper@gmail.com>
Date: Tue, 21 Feb 2023 13:13:01 -0800
Subject: [PATCH 6/6] Document the global fallback

---
 rayon-core/src/lib.rs | 18 +++++++++++++++++-
 src/lib.rs            |  5 +++++
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/rayon-core/src/lib.rs b/rayon-core/src/lib.rs
index d0d2ea406..8ef4d6b04 100644
--- a/rayon-core/src/lib.rs
+++ b/rayon-core/src/lib.rs
@@ -26,7 +26,23 @@
 //! [`join()`]: struct.ThreadPool.html#method.join
 //! [`ThreadPoolBuilder`]: struct.ThreadPoolBuilder.html
 //!
-//! ## Restricting multiple versions
+//! # Global fallback when threading is unsupported
+//!
+//! Rayon uses `std` APIs for threading, but some targets have incomplete implementations that
+//! always return `Unsupported` errors. The WebAssembly `wasm32-unknown-unknown` and `wasm32-wasi`
+//! targets are notable examples of this. Rather than panicking on the unsupported error when
+//! creating the implicit global threadpool, Rayon configures a fallback mode instead.
+//!
+//! This fallback mode mostly functions as if it were using a single-threaded "pool", like setting
+//! `RAYON_NUM_THREADS=1`. For example, `join` will execute its two closures sequentially, since
+//! there is no other thread to share the work. However, since the pool is not running independent
+//! of the main thread, non-blocking calls like `spawn` may not execute at all, unless a lower-
+//! priority call like `broadcast` gives them an opening. The fallback mode does not try to emulate
+//! anything like thread preemption or `async` task switching.
+//!
+//! Explicit `ThreadPoolBuilder` methods always report their error without any fallback.
+//!
+//! # Restricting multiple versions
 //!
 //! In order to ensure proper coordination between threadpools, and especially
 //! to make sure there's only one global threadpool, `rayon-core` is actively
diff --git a/src/lib.rs b/src/lib.rs
index 25a5e16a7..e35160b3e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -76,6 +76,11 @@
 //! [the `collections` from `std`]: https://doc.rust-lang.org/std/collections/index.html
 //! [`std`]: https://doc.rust-lang.org/std/
 //!
+//! # Targets without threading
+//!
+//! Rayon has limited support for targets without `std` threading implementations.
+//! See the [`rayon_core`] documentation for more information about its global fallback.
+//!
 //! # Other questions?
 //!
 //! See [the Rayon FAQ][faq].