cannon: Add more concurrency primitives tests (#12771)

* feat:Add more sync tests
Signed-off-by: Chen Kai <281165273grape@gmail.com>

* feat:add more sync tests
Signed-off-by: Chen Kai <281165273grape@gmail.com>

* fix:fix failed tests
Signed-off-by: Chen Kai <281165273grape@gmail.com>

* fix:add copyright credit and remove unused code
Signed-off-by: Chen Kai <281165273grape@gmail.com>

* fix:fix copyright format
Signed-off-by: Chen Kai <281165273grape@gmail.com>

* fix code review suggestions
Signed-off-by: Chen Kai <281165273grape@gmail.com>

---------
Signed-off-by: Chen Kai <281165273grape@gmail.com>

cannon/mipsevm/multithreaded/instrumented_test.go

@@ -36,12 +36,73 @@ func TestInstrumentedState_Claim(t *testing.T) {
 
 func TestInstrumentedState_MultithreadedProgram(t *testing.T) {
 	t.Parallel()
-	state, _ := testutil.LoadELFProgram(t, testutil.ProgramPath("multithreaded"), CreateInitialState, false)
+	cases := []struct {
+		name           string
+		expectedOutput []string
+		programName    string
+	}{
+		{
+			name: "wg and chan test",
+			expectedOutput: []string{
+				"waitgroup result: 42",
+				"channels result: 1234",
+			},
+			programName: "mt-wg",
+		},
+		{
+			name: "mutex test",
+			expectedOutput: []string{
+				"Mutex test passed",
+			},
+			programName: "mt-mutex",
+		},
+		{
+			name: "cond test",
+			expectedOutput: []string{
+				"Cond test passed",
+			},
+			programName: "mt-cond",
+		},
+		{
+			name: "rwmutex test",
+			expectedOutput: []string{
+				"RWMutex test passed",
+			},
+			programName: "mt-rwmutex",
+		},
+		{
+			name: "once test",
+			expectedOutput: []string{
+				"Once test passed",
+			},
+			programName: "mt-once",
+		},
+		{
+			name: "map test",
+			expectedOutput: []string{
+				"Map test passed",
+			},
+			programName: "mt-map",
+		},
+		{
+			name: "pool test",
+			expectedOutput: []string{
+				"Pool test passed",
+			},
+			programName: "mt-pool",
+		},
+	}
+
+	for _, test := range cases {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			t.Parallel()
+			state, _ := testutil.LoadELFProgram(t, testutil.ProgramPath(test.programName), CreateInitialState, false)
 			oracle := testutil.StaticOracle(t, []byte{})
 
 			var stdOutBuf, stdErrBuf bytes.Buffer
 			us := NewInstrumentedState(state, oracle, io.MultiWriter(&stdOutBuf, os.Stdout), io.MultiWriter(&stdErrBuf, os.Stderr), testutil.CreateLogger(), nil)
-	for i := 0; i < 2_000_000; i++ {
+			for i := 0; i < 5_000_000; i++ {
 				if us.GetState().GetExited() {
 					break
 				}
@@ -52,11 +113,13 @@ func TestInstrumentedState_MultithreadedProgram(t *testing.T) {
 
 			require.True(t, state.Exited, "must complete program")
 			require.Equal(t, uint8(0), state.ExitCode, "exit with 0")
-	require.Contains(t, "waitgroup result: 42", stdErrBuf.String())
-	require.Contains(t, "channels result: 1234", stdErrBuf.String())
+			for _, expected := range test.expectedOutput {
+				require.Contains(t, stdOutBuf.String(), expected)
+			}
 			require.Equal(t, "", stdErrBuf.String(), "should not print any errors")
+		})
+	}
 }
-
 func TestInstrumentedState_Alloc(t *testing.T) {
 	if os.Getenv("SKIP_SLOW_TESTS") == "true" {
 		t.Skip("Skipping slow test because SKIP_SLOW_TESTS is enabled")

cannon/testdata/example/multithreaded/go.mod → cannon/testdata/example/mt-cond/go.mod

-module multithreaded
+module cond
 
 go 1.22
 

cannon/testdata/example/mt-cond/main.go

+// Portions of this code are derived from code written by The Go Authors.
+// See original source: https://github.com/golang/go/blob/400433af3660905ecaceaf19ddad3e6c24b141df/src/sync/cond_test.go
+//
+// --- Original License Notice ---
+//
+// Copyright 2009 The Go Authors.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+package main
+
+import (
+	"fmt"
+	"os"
+	"reflect"
+	"runtime"
+	"sync"
+)
+
+func main() {
+	TestCondSignal()
+	TestCondSignalGenerations()
+	TestCondBroadcast()
+	TestRace()
+	TestCondSignalStealing()
+	TestCondCopy()
+
+	fmt.Println("Cond test passed")
+}
+
+func TestCondSignal() {
+	var m sync.Mutex
+	c := sync.NewCond(&m)
+	n := 2
+	running := make(chan bool, n)
+	awake := make(chan bool, n)
+	for i := 0; i < n; i++ {
+		go func() {
+			m.Lock()
+			running <- true
+			c.Wait()
+			awake <- true
+			m.Unlock()
+		}()
+	}
+	for i := 0; i < n; i++ {
+		<-running // Wait for everyone to run.
+	}
+	for n > 0 {
+		select {
+		case <-awake:
+			_, _ = fmt.Fprintln(os.Stderr, "goroutine not asleep")
+			os.Exit(1)
+		default:
+		}
+		m.Lock()
+		c.Signal()
+		m.Unlock()
+		<-awake // Will deadlock if no goroutine wakes up
+		select {
+		case <-awake:
+			_, _ = fmt.Fprintln(os.Stderr, "too many goroutines awake")
+			os.Exit(1)
+		default:
+		}
+		n--
+	}
+	c.Signal()
+}
+
+func TestCondSignalGenerations() {
+	var m sync.Mutex
+	c := sync.NewCond(&m)
+	n := 100
+	running := make(chan bool, n)
+	awake := make(chan int, n)
+	for i := 0; i < n; i++ {
+		go func(i int) {
+			m.Lock()
+			running <- true
+			c.Wait()
+			awake <- i
+			m.Unlock()
+		}(i)
+		if i > 0 {
+			a := <-awake
+			if a != i-1 {
+				_, _ = fmt.Fprintf(os.Stderr, "wrong goroutine woke up: want %d, got %d\n", i-1, a)
+				os.Exit(1)
+			}
+		}
+		<-running
+		m.Lock()
+		c.Signal()
+		m.Unlock()
+	}
+}
+
+func TestCondBroadcast() {
+	var m sync.Mutex
+	c := sync.NewCond(&m)
+	n := 5
+	running := make(chan int, n)
+	awake := make(chan int, n)
+	exit := false
+	for i := 0; i < n; i++ {
+		go func(g int) {
+			m.Lock()
+			for !exit {
+				running <- g
+				c.Wait()
+				awake <- g
+			}
+			m.Unlock()
+		}(i)
+	}
+	for i := 0; i < n; i++ {
+		for i := 0; i < n; i++ {
+			<-running // Will deadlock unless n are running.
+		}
+		if i == n-1 {
+			m.Lock()
+			exit = true
+			m.Unlock()
+		}
+		select {
+		case <-awake:
+			_, _ = fmt.Fprintln(os.Stderr, "goroutine not asleep")
+			os.Exit(1)
+		default:
+		}
+		m.Lock()
+		c.Broadcast()
+		m.Unlock()
+		seen := make([]bool, n)
+		for i := 0; i < n; i++ {
+			g := <-awake
+			if seen[g] {
+				_, _ = fmt.Fprintln(os.Stderr, "goroutine woke up twice")
+				os.Exit(1)
+			}
+			seen[g] = true
+		}
+	}
+	select {
+	case <-running:
+		_, _ = fmt.Fprintln(os.Stderr, "goroutine still running")
+		os.Exit(1)
+	default:
+	}
+	c.Broadcast()
+}
+
+func TestRace() {
+	x := 0
+	c := sync.NewCond(&sync.Mutex{})
+	done := make(chan bool)
+	go func() {
+		c.L.Lock()
+		x = 1
+		c.Wait()
+		if x != 2 {
+			_, _ = fmt.Fprintln(os.Stderr, "want 2")
+			os.Exit(1)
+		}
+		x = 3
+		c.Signal()
+		c.L.Unlock()
+		done <- true
+	}()
+	go func() {
+		c.L.Lock()
+		for {
+			if x == 1 {
+				x = 2
+				c.Signal()
+				break
+			}
+			c.L.Unlock()
+			runtime.Gosched()
+			c.L.Lock()
+		}
+		c.L.Unlock()
+		done <- true
+	}()
+	go func() {
+		c.L.Lock()
+		for {
+			if x == 2 {
+				c.Wait()
+				if x != 3 {
+					_, _ = fmt.Fprintln(os.Stderr, "want 3")
+					os.Exit(1)
+				}
+				break
+			}
+			if x == 3 {
+				break
+			}
+			c.L.Unlock()
+			runtime.Gosched()
+			c.L.Lock()
+		}
+		c.L.Unlock()
+		done <- true
+	}()
+	<-done
+	<-done
+	<-done
+}
+
+func TestCondSignalStealing() {
+	for iters := 0; iters < 5; iters++ {
+		var m sync.Mutex
+		cond := sync.NewCond(&m)
+
+		// Start a waiter.
+		ch := make(chan struct{})
+		go func() {
+			m.Lock()
+			ch <- struct{}{}
+			cond.Wait()
+			m.Unlock()
+
+			ch <- struct{}{}
+		}()
+
+		<-ch
+		m.Lock()
+		m.Unlock()
+
+		// We know that the waiter is in the cond.Wait() call because we
+		// synchronized with it, then acquired/released the mutex it was
+		// holding when we synchronized.
+		//
+		// Start two goroutines that will race: one will broadcast on
+		// the cond var, the other will wait on it.
+		//
+		// The new waiter may or may not get notified, but the first one
+		// has to be notified.
+		done := false
+		go func() {
+			cond.Broadcast()
+		}()
+
+		go func() {
+			m.Lock()
+			for !done {
+				cond.Wait()
+			}
+			m.Unlock()
+		}()
+
+		// Check that the first waiter does get signaled.
+		<-ch
+
+		// Release the second waiter in case it didn't get the
+		// broadcast.
+		m.Lock()
+		done = true
+		m.Unlock()
+		cond.Broadcast()
+	}
+}
+
+func TestCondCopy() {
+	defer func() {
+		err := recover()
+		if err == nil || err.(string) != "sync.Cond is copied" {
+			_, _ = fmt.Fprintf(os.Stderr, "got %v, expect sync.Cond is copied", err)
+			os.Exit(1)
+		}
+	}()
+	c := sync.Cond{L: &sync.Mutex{}}
+	c.Signal()
+	var c2 sync.Cond
+	reflect.ValueOf(&c2).Elem().Set(reflect.ValueOf(&c).Elem()) // c2 := c, hidden from vet
+	c2.Signal()
+}

cannon/testdata/example/mt-map/go.mod

+module map
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/mt-map/main.go

+package main
+
+import (
+	"fmt"
+	"sync"
+)
+
+func main() {
+	var m sync.Map
+
+	m.Store("hello", "world")
+	m.Store("foo", "bar")
+	m.Store("baz", "qux")
+
+	m.Delete("foo")
+	m.Load("baz")
+
+	go func() {
+		m.CompareAndDelete("hello", "world")
+		m.LoadAndDelete("baz")
+	}()
+
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			m.Load("hello")
+			m.Load("baz")
+			m.Range(func(k, v interface{}) bool {
+				m.Load("hello")
+				m.Load("baz")
+				return true
+			})
+			m.CompareAndSwap("hello", "world", "Go")
+			m.LoadOrStore("hello", "world")
+			wg.Done()
+		}()
+	}
+
+	wg.Wait()
+
+	fmt.Println("Map test passed")
+}

cannon/testdata/example/mt-mutex/go.mod

+module mutex
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/mt-mutex/main.go

+// Portions of this code are derived from code written by The Go Authors.
+// See original source: https://github.com/golang/go/blob/400433af3660905ecaceaf19ddad3e6c24b141df/src/sync/mutex_test.go
+//
+// --- Original License Notice ---
+//
+// Copyright 2009 The Go Authors.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+package main
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+func main() {
+	TestMutex()
+}
+
+func TestMutex() {
+	m := new(sync.Mutex)
+
+	m.Lock()
+	if m.TryLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryLock succeeded with mutex locked")
+		os.Exit(1)
+	}
+	m.Unlock()
+	if !m.TryLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryLock failed with mutex unlocked")
+		os.Exit(1)
+	}
+	m.Unlock()
+
+	c := make(chan bool)
+	for i := 0; i < 10; i++ {
+		go HammerMutex(m, 1000, c)
+	}
+	for i := 0; i < 10; i++ {
+		<-c
+	}
+	fmt.Println("Mutex test passed")
+}
+
+func HammerMutex(m *sync.Mutex, loops int, cdone chan bool) {
+	for i := 0; i < loops; i++ {
+		if i%3 == 0 {
+			if m.TryLock() {
+				m.Unlock()
+			}
+			continue
+		}
+		m.Lock()
+		m.Unlock()
+	}
+	cdone <- true
+}

cannon/testdata/example/mt-once/go.mod

+module once
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/mt-once/main.go

+// Portions of this code are derived from code written by The Go Authors.
+// See original source: https://github.com/golang/go/blob/400433af3660905ecaceaf19ddad3e6c24b141df/src/sync/once_test.go
+//
+// --- Original License Notice ---
+//
+// Copyright 2009 The Go Authors.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+package main
+
+import (
+	"fmt"
+	"os"
+	"sync"
+)
+
+func main() {
+	TestOnce()
+	TestOncePanic()
+
+	fmt.Println("Once test passed")
+}
+
+type one int
+
+func (o *one) Increment() {
+	*o++
+}
+
+func run(once *sync.Once, o *one, c chan bool) {
+	once.Do(func() { o.Increment() })
+	if v := *o; v != 1 {
+		_, _ = fmt.Fprintf(os.Stderr, "once failed inside run: %d is not 1\n", v)
+		os.Exit(1)
+	}
+	c <- true
+}
+
+func TestOnce() {
+	o := new(one)
+	once := new(sync.Once)
+	c := make(chan bool)
+	const N = 10
+	for i := 0; i < N; i++ {
+		go run(once, o, c)
+	}
+	for i := 0; i < N; i++ {
+		<-c
+	}
+	if *o != 1 {
+		_, _ = fmt.Fprintf(os.Stderr, "once failed outside run: %d is not 1\n", *o)
+		os.Exit(1)
+	}
+}
+
+func TestOncePanic() {
+	var once sync.Once
+	func() {
+		defer func() {
+			if r := recover(); r == nil {
+				_, _ = fmt.Fprintf(os.Stderr, "Once.Do did not panic")
+				os.Exit(1)
+			}
+		}()
+		once.Do(func() {
+			panic("failed")
+		})
+	}()
+
+	once.Do(func() {
+		_, _ = fmt.Fprintf(os.Stderr, "Once.Do called twice")
+		os.Exit(1)
+	})
+}

cannon/testdata/example/mt-pool/go.mod

+module pool
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/mt-pool/main.go

+package main
+
+import (
+	"fmt"
+	"sync"
+)
+
+func main() {
+	var x sync.Pool
+
+	x.Put(1)
+	x.Put(2)
+
+	// try some concurrency!
+	var wg sync.WaitGroup
+	wg.Add(2)
+	go func() {
+		x.Put(3)
+		wg.Done()
+	}()
+	go func() {
+		x.Put(4)
+		wg.Done()
+	}()
+
+	wg.Wait()
+
+	wg.Add(4)
+	for i := 0; i < 4; i++ {
+		go func() {
+			x.Get()
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+
+	fmt.Println("Pool test passed")
+}

cannon/testdata/example/mt-rwmutex/go.mod

+module rwmutex
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/mt-rwmutex/main.go

+// Portions of this code are derived from code written by The Go Authors.
+// See original source: https://github.com/golang/go/blob/400433af3660905ecaceaf19ddad3e6c24b141df/src/sync/rwmutex_test.go
+//
+// --- Original License Notice ---
+//
+// Copyright 2009 The Go Authors.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+// * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+// * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+// * Neither the name of Google LLC nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+package main
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"sync"
+	"sync/atomic"
+)
+
+func main() {
+	TestParallelReaders()
+	TestRLocker()
+	TestRWMutex()
+
+	fmt.Println("RWMutex test passed")
+}
+
+func parallelReader(m *sync.RWMutex, clocked, cunlock, cdone chan bool) {
+	m.RLock()
+	clocked <- true
+	<-cunlock
+	m.RUnlock()
+	cdone <- true
+}
+
+func doTestParallelReaders(numReaders, gomaxprocs int) {
+	runtime.GOMAXPROCS(gomaxprocs)
+	var m sync.RWMutex
+	clocked := make(chan bool)
+	cunlock := make(chan bool)
+	cdone := make(chan bool)
+	for i := 0; i < numReaders; i++ {
+		go parallelReader(&m, clocked, cunlock, cdone)
+	}
+	// Wait for all parallel RLock()s to succeed.
+	for i := 0; i < numReaders; i++ {
+		<-clocked
+	}
+	for i := 0; i < numReaders; i++ {
+		cunlock <- true
+	}
+	// Wait for the goroutines to finish.
+	for i := 0; i < numReaders; i++ {
+		<-cdone
+	}
+}
+
+func TestParallelReaders() {
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(-1))
+	doTestParallelReaders(1, 4)
+	doTestParallelReaders(3, 4)
+	doTestParallelReaders(4, 2)
+}
+
+func reader(rwm *sync.RWMutex, num_iterations int, activity *int32, cdone chan bool) {
+	for i := 0; i < num_iterations; i++ {
+		rwm.RLock()
+		n := atomic.AddInt32(activity, 1)
+		if n < 1 || n >= 10000 {
+			rwm.RUnlock()
+			panic(fmt.Sprintf("wlock(%d)\n", n))
+		}
+		for i := 0; i < 100; i++ {
+		}
+		atomic.AddInt32(activity, -1)
+		rwm.RUnlock()
+	}
+	cdone <- true
+}
+
+func writer(rwm *sync.RWMutex, num_iterations int, activity *int32, cdone chan bool) {
+	for i := 0; i < num_iterations; i++ {
+		rwm.Lock()
+		n := atomic.AddInt32(activity, 10000)
+		if n != 10000 {
+			rwm.Unlock()
+			panic(fmt.Sprintf("wlock(%d)\n", n))
+		}
+		for i := 0; i < 100; i++ {
+		}
+		atomic.AddInt32(activity, -10000)
+		rwm.Unlock()
+	}
+	cdone <- true
+}
+
+func HammerRWMutex(gomaxprocs, numReaders, num_iterations int) {
+	runtime.GOMAXPROCS(gomaxprocs)
+	// Number of active readers + 10000 * number of active writers.
+	var activity int32
+	var rwm sync.RWMutex
+	cdone := make(chan bool)
+	go writer(&rwm, num_iterations, &activity, cdone)
+	var i int
+	for i = 0; i < numReaders/2; i++ {
+		go reader(&rwm, num_iterations, &activity, cdone)
+	}
+	go writer(&rwm, num_iterations, &activity, cdone)
+	for ; i < numReaders; i++ {
+		go reader(&rwm, num_iterations, &activity, cdone)
+	}
+	// Wait for the 2 writers and all readers to finish.
+	for i := 0; i < 2+numReaders; i++ {
+		<-cdone
+	}
+}
+
+func TestRWMutex() {
+	var m sync.RWMutex
+
+	m.Lock()
+	if m.TryLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryLock succeeded with mutex locked")
+		os.Exit(1)
+	}
+	if m.TryRLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryRLock succeeded with mutex locked")
+		os.Exit(1)
+	}
+	m.Unlock()
+
+	if !m.TryLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryLock failed with mutex unlocked")
+		os.Exit(1)
+	}
+	m.Unlock()
+
+	if !m.TryRLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryRLock failed with mutex unlocked")
+		os.Exit(1)
+	}
+	if !m.TryRLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryRLock failed with mutex unlocked")
+		os.Exit(1)
+	}
+	if m.TryLock() {
+		_, _ = fmt.Fprintln(os.Stderr, "TryLock succeeded with mutex rlocked")
+		os.Exit(1)
+	}
+	m.RUnlock()
+	m.RUnlock()
+
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(-1))
+	n := 5
+
+	HammerRWMutex(1, 1, n)
+	HammerRWMutex(1, 3, n)
+	HammerRWMutex(1, 10, n)
+	HammerRWMutex(4, 1, n)
+	HammerRWMutex(4, 3, n)
+	HammerRWMutex(4, 10, n)
+	HammerRWMutex(10, 1, n)
+	HammerRWMutex(10, 3, n)
+	HammerRWMutex(10, 10, n)
+	HammerRWMutex(10, 5, n)
+}
+
+func TestRLocker() {
+	var wl sync.RWMutex
+	var rl sync.Locker
+	wlocked := make(chan bool, 1)
+	rlocked := make(chan bool, 1)
+	rl = wl.RLocker()
+	n := 10
+	go func() {
+		for i := 0; i < n; i++ {
+			rl.Lock()
+			rl.Lock()
+			rlocked <- true
+			wl.Lock()
+			wlocked <- true
+		}
+	}()
+	for i := 0; i < n; i++ {
+		<-rlocked
+		rl.Unlock()
+		select {
+		case <-wlocked:
+			_, _ = fmt.Fprintln(os.Stderr, "RLocker() didn't read-lock it")
+			os.Exit(1)
+		default:
+		}
+		rl.Unlock()
+		<-wlocked
+		select {
+		case <-rlocked:
+			_, _ = fmt.Fprintln(os.Stderr, "RLocker() didn't respect the write lock")
+			os.Exit(1)
+		default:
+		}
+		wl.Unlock()
+	}
+}

cannon/testdata/example/mt-wg/go.mod

+module wg
+
+go 1.22
+
+toolchain go1.22.0

cannon/testdata/example/multithreaded/main.go → cannon/testdata/example/mt-wg/main.go

@@ -2,8 +2,6 @@ package main
 
 import (
 	"fmt"
-	"os"
-	"runtime"
 	"sync"
 	"sync/atomic"
 )
@@ -39,8 +37,4 @@ func main() {
 	a <- 1234
 	out := <-c
 	fmt.Printf("channels result: %d\n", out)
-
-	// try a GC! (the runtime might not have run one yet)
-	runtime.GC()
-	_, _ = os.Stdout.Write([]byte("GC complete!\n"))
 }