feat: JSPI support for wasm32-unknown-emscripten

.github/workflows/ci.yml

@@ -19,6 +19,8 @@ env:
   rust_nightly: nightly-2025-10-12
   # Pin a specific miri version
   rust_miri_nightly: nightly-2026-06-29
+  rust_emscripten_nightly: nightly-2026-08-17
+  emsdk_version: '6.0.8'
   rust_clippy: '1.88'
   # When updating this, also update:
   # - README.md
@@ -509,7 +511,7 @@ jobs:
           # We don't care about the semver of unstable tokio features.
           features: ${{ env.TOKIO_STABLE_FEATURES }}
       - name: Check semver for rest of the workspace
-        if: ${{ !startsWith(github.event.pull_request.base.ref, 'tokio-1.') }}
+        if: ${{ !startsWith(github.event.pull_request.base.ref, 'tokio-1.') && !startsWith(github.ref_name, 'tokio-1.') }}
         uses: obi1kenobi/cargo-semver-checks-action@v2
         with:
           rust-toolchain: ${{ env.rust_stable }}
@@ -1180,9 +1182,9 @@ jobs:
       - name: Install cargo-nextest, wasmtime
         uses: taiki-e/install-action@v2
         with:
-          # Wasmtime v47.0.0 or later should work, but we stick with a known,
+          # Wasmtime v48.0.0 or later should work, but we stick with a known,
           # specific version to avoid surprises:
-          tool: cargo-nextest,wasmtime-cli@47.0.2
+          tool: cargo-nextest,wasmtime-cli@48.0.2
 
       - uses: Swatinem/rust-cache@v2
 
@@ -1193,6 +1195,66 @@ jobs:
           RUSTFLAGS: --cfg tokio_unstable
           CARGO_TARGET_WASM32_WASIP2_RUNNER: wasmtime run -Sinherit-network
 
+  wasm32-unknown-emscripten:
+    name: test tokio for wasm32-unknown-emscripten
+    needs: basics
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - name: Install Rust ${{ env.rust_stable }}
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ env.rust_stable }}
+          targets: wasm32-unknown-emscripten
+
+      - name: Install Emscripten
+        uses: emscripten-core/setup-emsdk@v16
+        with:
+          version: ${{ env.emsdk_version }}
+
+      - uses: actions/setup-node@v7
+        with:
+          node-version: 26
+
+      - uses: Swatinem/rust-cache@v2
+
+      - name: Install cargo-hack
+        uses: taiki-e/install-action@v2
+        with:
+          tool: cargo-hack
+
+      - name: Check tokio feature matrix for emscripten
+        run: cargo hack check -p tokio --each-feature --exclude-features full,net,process,signal,rt-multi-thread,io-uring,taskdump,schedule-latency --target wasm32-unknown-emscripten
+        working-directory: tokio
+
+      - name: Test tokio for emscripten (JSPI)
+        run: cargo test -p tokio --target wasm32-unknown-emscripten --features "rt,time,sync,macros,fs,io-util,io-std,test-util" --tests
+        working-directory: tokio
+        env:
+          CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER: node
+          RUSTFLAGS: "-Dwarnings -Clink-args=-sALLOW_MEMORY_GROWTH=1 -Clink-args=-sEXIT_RUNTIME=1 -Clink-args=-sJSPI -Clink-args=-sSTACK_SIZE=1048576"
+
+      - name: Test tokio for emscripten (non-JSPI)
+        run: cargo test -p tokio --target wasm32-unknown-emscripten --features "rt,time,sync,macros,fs,io-util,io-std,test-util" --test rt_emscripten_block_on --test sync_emscripten_blocking
+        working-directory: tokio
+        env:
+          CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER: node
+          RUSTFLAGS: "-Dwarnings -Clink-args=-sALLOW_MEMORY_GROWTH=1 -Clink-args=-sEXIT_RUNTIME=1 -Clink-args=-sSTACK_SIZE=1048576"
+
+      - name: Install Rust ${{ env.rust_emscripten_nightly }}
+        uses: dtolnay/rust-toolchain@nightly
+        with:
+          toolchain: ${{ env.rust_emscripten_nightly }}
+          targets: wasm32-unknown-emscripten
+          components: rust-src
+
+      - name: Test tokio for emscripten (pthreads)
+        run: cargo +${{ env.rust_emscripten_nightly }} test -Zbuild-std=std,panic_abort -p tokio --target wasm32-unknown-emscripten --features "rt,rt-multi-thread,time,sync,macros,fs,io-util,io-std,test-util" --tests
+        working-directory: tokio
+        env:
+          CARGO_TARGET_WASM32_UNKNOWN_EMSCRIPTEN_RUNNER: node
+          RUSTFLAGS: "-Dwarnings -Ctarget-feature=+atomics,+bulk-memory,+mutable-globals -Clink-args=-pthread -Clink-args=-sPTHREAD_POOL_SIZE=8 -Clink-args=-sINITIAL_MEMORY=134217728 -Clink-args=-sEXIT_RUNTIME=1 -Clink-args=-sSTACK_SIZE=1048576"
+
   check-external-types:
     name: check-external-types (${{ matrix.os }})
     needs: basics
@@ -1352,7 +1414,7 @@ jobs:
       - name: Test in FreeBSD
         uses: vmactions/freebsd-vm@v1
         with:
-          release: '14.4'
+          release: '14.5'
           envs: "TOKIO_STABLE_FEATURES RUSTFLAGS"
           sync: rsync
           copyback: false
@@ -1381,7 +1443,7 @@ jobs:
           RUSTFLAGS: --cfg docsrs --cfg tokio_unstable
           RUSTDOCFLAGS: --cfg docsrs --cfg tokio_unstable -Dwarnings
         with:
-          release: '14.4'
+          release: '14.5'
           envs: "TOKIO_STABLE_FEATURES RUSTDOCFLAGS RUSTFLAGS"
           sync: rsync
           copyback: false
@@ -1406,7 +1468,7 @@ jobs:
       - name: Test in FreeBSD
         uses: vmactions/freebsd-vm@v1
         with:
-          release: '14.4'
+          release: '14.5'
           envs: "TOKIO_STABLE_FEATURES RUSTFLAGS"
           sync: rsync
           copyback: false

.github/workflows/uring-kernel-version-test.yml

@@ -81,6 +81,7 @@ jobs:
           mount -t sysfs sysfs /sys
           mkdir -p /tmp && mount -t tmpfs -o mode=1777 tmpfs /tmp
           for f in /bin/tests/*; do RUST_BACKTRACE=1 "$f" ; done
+          echo "ALL_TESTS_COMPLETED"
           EOF
           chmod +x initramfs/init
 
@@ -94,11 +95,14 @@ jobs:
           set -euo pipefail
 
           set +e
+          # 3 GiB guest (the runner has 16 GB): the initramfs holds ~760 MB of
+          # unstripped test binaries, and `open_many_files` in `fs_uring` had
+          # 200-340 MB of anon RSS when the 1 GiB guest OOM-killed it.
           qemu-system-x86_64 \
             -kernel linux-${{ env.KERNEL_VERSION }}/arch/x86/boot/bzImage \
             -initrd initramfs.cpio.gz \
             -append "console=ttyS0 rootfstype=ramfs panic=1" \
-            -nographic -no-reboot -m 1024 -action panic=exit-failure 2>&1 | tee qemu-output.log
+            -nographic -no-reboot -m 3072 -action panic=exit-failure 2>&1 | tee qemu-output.log
           qemu_status=${PIPESTATUS[0]} tee_status=${PIPESTATUS[1]}
           set -e
 
@@ -115,6 +119,14 @@ jobs:
           if grep -q "test result: FAILED" qemu-output.log; then
             echo "tests reported failures"
             exit 1
-          else
-            echo "all tests passed"
           fi
+
+          # A binary killed before it prints its summary (OOM, panic in init)
+          # never writes `test result: FAILED`, so also require the marker that
+          # init prints after the last binary.
+          if ! grep -q "ALL_TESTS_COMPLETED" qemu-output.log; then
+            echo "tests did not run to completion"
+            exit 1
+          fi
+
+          echo "all tests passed"

README.md

@@ -217,18 +217,18 @@ warrants a patch release with a fix for the bug, it will be backported and
 released as a new patch release for each LTS minor version. Our current LTS
 releases are:
 
- * `1.47.x` - LTS release until September 2026. (MSRV 1.70)
  * `1.51.x` - LTS release until March 2027. (MSRV 1.71)
+ * `1.53.x` - LTS release until September 2027. (MSRV 1.71)
 
 Each LTS release will continue to receive backported fixes for at least a year.
 If you wish to use a fixed minor release in your project, we recommend that you
 use an LTS release.
 
 To use a fixed minor version, you can specify the version with a tilde. For
-example, to specify that you wish to use the newest `1.47.x` patch release, you
+example, to specify that you wish to use the newest `1.51.x` patch release, you
 can use the following dependency specification:
 ```text
-tokio = { version = "~1.47", features = [...] }
+tokio = { version = "~1.51", features = [...] }
 ```
 
 ### Previous LTS releases
@@ -242,6 +242,7 @@ tokio = { version = "~1.47", features = [...] }
  * `1.36.x` - LTS release until March 2025.
  * `1.38.x` - LTS release until July 2025.
  * `1.43.x` - LTS release until March 2026.
+ * `1.47.x` - LTS release until September 2026.
 
 ## License
 

benches/Cargo.toml

@@ -106,5 +106,10 @@ name = "remote_spawn"
 path = "remote_spawn.rs"
 harness = false
 
+[[bench]]
+name = "net_accept"
+path = "net_accept.rs"
+harness = false
+
 [lints]
 workspace = true