Source file src/runtime/chan_test.go

Documentation: runtime

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package runtime_test
     6  
     7  import (
     8  	"internal/testenv"
     9  	"math"
    10  	"runtime"
    11  	"sync"
    12  	"sync/atomic"
    13  	"testing"
    14  	"time"
    15  )
    16  
    17  func TestChan(t *testing.T) {
    18  	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(4))
    19  	N := 200
    20  	if testing.Short() {
    21  		N = 20
    22  	}
    23  	for chanCap := 0; chanCap < N; chanCap++ {
    24  		{
    25  			// Ensure that receive from empty chan blocks.
    26  			c := make(chan int, chanCap)
    27  			recv1 := false
    28  			go func() {
    29  				_ = <-c
    30  				recv1 = true
    31  			}()
    32  			recv2 := false
    33  			go func() {
    34  				_, _ = <-c
    35  				recv2 = true
    36  			}()
    37  			time.Sleep(time.Millisecond)
    38  			if recv1 || recv2 {
    39  				t.Fatalf("chan[%d]: receive from empty chan", chanCap)
    40  			}
    41  			// Ensure that non-blocking receive does not block.
    42  			select {
    43  			case _ = <-c:
    44  				t.Fatalf("chan[%d]: receive from empty chan", chanCap)
    45  			default:
    46  			}
    47  			select {
    48  			case _, _ = <-c:
    49  				t.Fatalf("chan[%d]: receive from empty chan", chanCap)
    50  			default:
    51  			}
    52  			c <- 0
    53  			c <- 0
    54  		}
    55  
    56  		{
    57  			// Ensure that send to full chan blocks.
    58  			c := make(chan int, chanCap)
    59  			for i := 0; i < chanCap; i++ {
    60  				c <- i
    61  			}
    62  			sent := uint32(0)
    63  			go func() {
    64  				c <- 0
    65  				atomic.StoreUint32(&sent, 1)
    66  			}()
    67  			time.Sleep(time.Millisecond)
    68  			if atomic.LoadUint32(&sent) != 0 {
    69  				t.Fatalf("chan[%d]: send to full chan", chanCap)
    70  			}
    71  			// Ensure that non-blocking send does not block.
    72  			select {
    73  			case c <- 0:
    74  				t.Fatalf("chan[%d]: send to full chan", chanCap)
    75  			default:
    76  			}
    77  			<-c
    78  		}
    79  
    80  		{
    81  			// Ensure that we receive 0 from closed chan.
    82  			c := make(chan int, chanCap)
    83  			for i := 0; i < chanCap; i++ {
    84  				c <- i
    85  			}
    86  			close(c)
    87  			for i := 0; i < chanCap; i++ {
    88  				v := <-c
    89  				if v != i {
    90  					t.Fatalf("chan[%d]: received %v, expected %v", chanCap, v, i)
    91  				}
    92  			}
    93  			if v := <-c; v != 0 {
    94  				t.Fatalf("chan[%d]: received %v, expected %v", chanCap, v, 0)
    95  			}
    96  			if v, ok := <-c; v != 0 || ok {
    97  				t.Fatalf("chan[%d]: received %v/%v, expected %v/%v", chanCap, v, ok, 0, false)
    98  			}
    99  		}
   100  
   101  		{
   102  			// Ensure that close unblocks receive.
   103  			c := make(chan int, chanCap)
   104  			done := make(chan bool)
   105  			go func() {
   106  				v, ok := <-c
   107  				done <- v == 0 && ok == false
   108  			}()
   109  			time.Sleep(time.Millisecond)
   110  			close(c)
   111  			if !<-done {
   112  				t.Fatalf("chan[%d]: received non zero from closed chan", chanCap)
   113  			}
   114  		}
   115  
   116  		{
   117  			// Send 100 integers,
   118  			// ensure that we receive them non-corrupted in FIFO order.
   119  			c := make(chan int, chanCap)
   120  			go func() {
   121  				for i := 0; i < 100; i++ {
   122  					c <- i
   123  				}
   124  			}()
   125  			for i := 0; i < 100; i++ {
   126  				v := <-c
   127  				if v != i {
   128  					t.Fatalf("chan[%d]: received %v, expected %v", chanCap, v, i)
   129  				}
   130  			}
   131  
   132  			// Same, but using recv2.
   133  			go func() {
   134  				for i := 0; i < 100; i++ {
   135  					c <- i
   136  				}
   137  			}()
   138  			for i := 0; i < 100; i++ {
   139  				v, ok := <-c
   140  				if !ok {
   141  					t.Fatalf("chan[%d]: receive failed, expected %v", chanCap, i)
   142  				}
   143  				if v != i {
   144  					t.Fatalf("chan[%d]: received %v, expected %v", chanCap, v, i)
   145  				}
   146  			}
   147  
   148  			// Send 1000 integers in 4 goroutines,
   149  			// ensure that we receive what we send.
   150  			const P = 4
   151  			const L = 1000
   152  			for p := 0; p < P; p++ {
   153  				go func() {
   154  					for i := 0; i < L; i++ {
   155  						c <- i
   156  					}
   157  				}()
   158  			}
   159  			done := make(chan map[int]int)
   160  			for p := 0; p < P; p++ {
   161  				go func() {
   162  					recv := make(map[int]int)
   163  					for i := 0; i < L; i++ {
   164  						v := <-c
   165  						recv[v] = recv[v] + 1
   166  					}
   167  					done <- recv
   168  				}()
   169  			}
   170  			recv := make(map[int]int)
   171  			for p := 0; p < P; p++ {
   172  				for k, v := range <-done {
   173  					recv[k] = recv[k] + v
   174  				}
   175  			}
   176  			if len(recv) != L {
   177  				t.Fatalf("chan[%d]: received %v values, expected %v", chanCap, len(recv), L)
   178  			}
   179  			for _, v := range recv {
   180  				if v != P {
   181  					t.Fatalf("chan[%d]: received %v values, expected %v", chanCap, v, P)
   182  				}
   183  			}
   184  		}
   185  
   186  		{
   187  			// Test len/cap.
   188  			c := make(chan int, chanCap)
   189  			if len(c) != 0 || cap(c) != chanCap {
   190  				t.Fatalf("chan[%d]: bad len/cap, expect %v/%v, got %v/%v", chanCap, 0, chanCap, len(c), cap(c))
   191  			}
   192  			for i := 0; i < chanCap; i++ {
   193  				c <- i
   194  			}
   195  			if len(c) != chanCap || cap(c) != chanCap {
   196  				t.Fatalf("chan[%d]: bad len/cap, expect %v/%v, got %v/%v", chanCap, chanCap, chanCap, len(c), cap(c))
   197  			}
   198  		}
   199  
   200  	}
   201  }
   202  
   203  func TestNonblockRecvRace(t *testing.T) {
   204  	n := 10000
   205  	if testing.Short() {
   206  		n = 100
   207  	}
   208  	for i := 0; i < n; i++ {
   209  		c := make(chan int, 1)
   210  		c <- 1
   211  		go func() {
   212  			select {
   213  			case <-c:
   214  			default:
   215  				t.Error("chan is not ready")
   216  			}
   217  		}()
   218  		close(c)
   219  		<-c
   220  		if t.Failed() {
   221  			return
   222  		}
   223  	}
   224  }
   225  
   226  // This test checks that select acts on the state of the channels at one
   227  // moment in the execution, not over a smeared time window.
   228  // In the test, one goroutine does:
   229  //	create c1, c2
   230  //	make c1 ready for receiving
   231  //	create second goroutine
   232  //	make c2 ready for receiving
   233  //	make c1 no longer ready for receiving (if possible)
   234  // The second goroutine does a non-blocking select receiving from c1 and c2.
   235  // From the time the second goroutine is created, at least one of c1 and c2
   236  // is always ready for receiving, so the select in the second goroutine must
   237  // always receive from one or the other. It must never execute the default case.
   238  func TestNonblockSelectRace(t *testing.T) {
   239  	n := 100000
   240  	if testing.Short() {
   241  		n = 1000
   242  	}
   243  	done := make(chan bool, 1)
   244  	for i := 0; i < n; i++ {
   245  		c1 := make(chan int, 1)
   246  		c2 := make(chan int, 1)
   247  		c1 <- 1
   248  		go func() {
   249  			select {
   250  			case <-c1:
   251  			case <-c2:
   252  			default:
   253  				done <- false
   254  				return
   255  			}
   256  			done <- true
   257  		}()
   258  		c2 <- 1
   259  		select {
   260  		case <-c1:
   261  		default:
   262  		}
   263  		if !<-done {
   264  			t.Fatal("no chan is ready")
   265  		}
   266  	}
   267  }
   268  
   269  // Same as TestNonblockSelectRace, but close(c2) replaces c2 <- 1.
   270  func TestNonblockSelectRace2(t *testing.T) {
   271  	n := 100000
   272  	if testing.Short() {
   273  		n = 1000
   274  	}
   275  	done := make(chan bool, 1)
   276  	for i := 0; i < n; i++ {
   277  		c1 := make(chan int, 1)
   278  		c2 := make(chan int)
   279  		c1 <- 1
   280  		go func() {
   281  			select {
   282  			case <-c1:
   283  			case <-c2:
   284  			default:
   285  				done <- false
   286  				return
   287  			}
   288  			done <- true
   289  		}()
   290  		close(c2)
   291  		select {
   292  		case <-c1:
   293  		default:
   294  		}
   295  		if !<-done {
   296  			t.Fatal("no chan is ready")
   297  		}
   298  	}
   299  }
   300  
   301  func TestSelfSelect(t *testing.T) {
   302  	// Ensure that send/recv on the same chan in select
   303  	// does not crash nor deadlock.
   304  	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
   305  	for _, chanCap := range []int{0, 10} {
   306  		var wg sync.WaitGroup
   307  		wg.Add(2)
   308  		c := make(chan int, chanCap)
   309  		for p := 0; p < 2; p++ {
   310  			p := p
   311  			go func() {
   312  				defer wg.Done()
   313  				for i := 0; i < 1000; i++ {
   314  					if p == 0 || i%2 == 0 {
   315  						select {
   316  						case c <- p:
   317  						case v := <-c:
   318  							if chanCap == 0 && v == p {
   319  								t.Errorf("self receive")
   320  								return
   321  							}
   322  						}
   323  					} else {
   324  						select {
   325  						case v := <-c:
   326  							if chanCap == 0 && v == p {
   327  								t.Errorf("self receive")
   328  								return
   329  							}
   330  						case c <- p:
   331  						}
   332  					}
   333  				}
   334  			}()
   335  		}
   336  		wg.Wait()
   337  	}
   338  }
   339  
   340  func TestSelectStress(t *testing.T) {
   341  	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(10))
   342  	var c [4]chan int
   343  	c[0] = make(chan int)
   344  	c[1] = make(chan int)
   345  	c[2] = make(chan int, 2)
   346  	c[3] = make(chan int, 3)
   347  	N := int(1e5)
   348  	if testing.Short() {
   349  		N /= 10
   350  	}
   351  	// There are 4 goroutines that send N values on each of the chans,
   352  	// + 4 goroutines that receive N values on each of the chans,
   353  	// + 1 goroutine that sends N values on each of the chans in a single select,
   354  	// + 1 goroutine that receives N values on each of the chans in a single select.
   355  	// All these sends, receives and selects interact chaotically at runtime,
   356  	// but we are careful that this whole construct does not deadlock.
   357  	var wg sync.WaitGroup
   358  	wg.Add(10)
   359  	for k := 0; k < 4; k++ {
   360  		k := k
   361  		go func() {
   362  			for i := 0; i < N; i++ {
   363  				c[k] <- 0
   364  			}
   365  			wg.Done()
   366  		}()
   367  		go func() {
   368  			for i := 0; i < N; i++ {
   369  				<-c[k]
   370  			}
   371  			wg.Done()
   372  		}()
   373  	}
   374  	go func() {
   375  		var n [4]int
   376  		c1 := c
   377  		for i := 0; i < 4*N; i++ {
   378  			select {
   379  			case c1[3] <- 0:
   380  				n[3]++
   381  				if n[3] == N {
   382  					c1[3] = nil
   383  				}
   384  			case c1[2] <- 0:
   385  				n[2]++
   386  				if n[2] == N {
   387  					c1[2] = nil
   388  				}
   389  			case c1[0] <- 0:
   390  				n[0]++
   391  				if n[0] == N {
   392  					c1[0] = nil
   393  				}
   394  			case c1[1] <- 0:
   395  				n[1]++
   396  				if n[1] == N {
   397  					c1[1] = nil
   398  				}
   399  			}
   400  		}
   401  		wg.Done()
   402  	}()
   403  	go func() {
   404  		var n [4]int
   405  		c1 := c
   406  		for i := 0; i < 4*N; i++ {
   407  			select {
   408  			case <-c1[0]:
   409  				n[0]++
   410  				if n[0] == N {
   411  					c1[0] = nil
   412  				}
   413  			case <-c1[1]:
   414  				n[1]++
   415  				if n[1] == N {
   416  					c1[1] = nil
   417  				}
   418  			case <-c1[2]:
   419  				n[2]++
   420  				if n[2] == N {
   421  					c1[2] = nil
   422  				}
   423  			case <-c1[3]:
   424  				n[3]++
   425  				if n[3] == N {
   426  					c1[3] = nil
   427  				}
   428  			}
   429  		}
   430  		wg.Done()
   431  	}()
   432  	wg.Wait()
   433  }
   434  
   435  func TestSelectFairness(t *testing.T) {
   436  	const trials = 10000
   437  	if runtime.GOOS == "linux" && runtime.GOARCH == "ppc64le" {
   438  		testenv.SkipFlaky(t, 22047)
   439  	}
   440  	c1 := make(chan byte, trials+1)
   441  	c2 := make(chan byte, trials+1)
   442  	for i := 0; i < trials+1; i++ {
   443  		c1 <- 1
   444  		c2 <- 2
   445  	}
   446  	c3 := make(chan byte)
   447  	c4 := make(chan byte)
   448  	out := make(chan byte)
   449  	done := make(chan byte)
   450  	var wg sync.WaitGroup
   451  	wg.Add(1)
   452  	go func() {
   453  		defer wg.Done()
   454  		for {
   455  			var b byte
   456  			select {
   457  			case b = <-c3:
   458  			case b = <-c4:
   459  			case b = <-c1:
   460  			case b = <-c2:
   461  			}
   462  			select {
   463  			case out <- b:
   464  			case <-done:
   465  				return
   466  			}
   467  		}
   468  	}()
   469  	cnt1, cnt2 := 0, 0
   470  	for i := 0; i < trials; i++ {
   471  		switch b := <-out; b {
   472  		case 1:
   473  			cnt1++
   474  		case 2:
   475  			cnt2++
   476  		default:
   477  			t.Fatalf("unexpected value %d on channel", b)
   478  		}
   479  	}
   480  	// If the select in the goroutine is fair,
   481  	// cnt1 and cnt2 should be about the same value.
   482  	// With 10,000 trials, the expected margin of error at
   483  	// a confidence level of six nines is 4.891676 / (2 * Sqrt(10000)).
   484  	r := float64(cnt1) / trials
   485  	e := math.Abs(r - 0.5)
   486  	t.Log(cnt1, cnt2, r, e)
   487  	if e > 4.891676/(2*math.Sqrt(trials)) {
   488  		t.Errorf("unfair select: in %d trials, results were %d, %d", trials, cnt1, cnt2)
   489  	}
   490  	close(done)
   491  	wg.Wait()
   492  }
   493  
   494  func TestChanSendInterface(t *testing.T) {
   495  	type mt struct{}
   496  	m := &mt{}
   497  	c := make(chan interface{}, 1)
   498  	c <- m
   499  	select {
   500  	case c <- m:
   501  	default:
   502  	}
   503  	select {
   504  	case c <- m:
   505  	case c <- &mt{}:
   506  	default:
   507  	}
   508  }
   509  
   510  func TestPseudoRandomSend(t *testing.T) {
   511  	n := 100
   512  	for _, chanCap := range []int{0, n} {
   513  		c := make(chan int, chanCap)
   514  		l := make([]int, n)
   515  		var m sync.Mutex
   516  		m.Lock()
   517  		go func() {
   518  			for i := 0; i < n; i++ {
   519  				runtime.Gosched()
   520  				l[i] = <-c
   521  			}
   522  			m.Unlock()
   523  		}()
   524  		for i := 0; i < n; i++ {
   525  			select {
   526  			case c <- 1:
   527  			case c <- 0:
   528  			}
   529  		}
   530  		m.Lock() // wait
   531  		n0 := 0
   532  		n1 := 0
   533  		for _, i := range l {
   534  			n0 += (i + 1) % 2
   535  			n1 += i
   536  		}
   537  		if n0 <= n/10 || n1 <= n/10 {
   538  			t.Errorf("Want pseudorandom, got %d zeros and %d ones (chan cap %d)", n0, n1, chanCap)
   539  		}
   540  	}
   541  }
   542  
   543  func TestMultiConsumer(t *testing.T) {
   544  	const nwork = 23
   545  	const niter = 271828
   546  
   547  	pn := []int{2, 3, 7, 11, 13, 17, 19, 23, 27, 31}
   548  
   549  	q := make(chan int, nwork*3)
   550  	r := make(chan int, nwork*3)
   551  
   552  	// workers
   553  	var wg sync.WaitGroup
   554  	for i := 0; i < nwork; i++ {
   555  		wg.Add(1)
   556  		go func(w int) {
   557  			for v := range q {
   558  				// mess with the fifo-ish nature of range
   559  				if pn[w%len(pn)] == v {
   560  					runtime.Gosched()
   561  				}
   562  				r <- v
   563  			}
   564  			wg.Done()
   565  		}(i)
   566  	}
   567  
   568  	// feeder & closer
   569  	expect := 0
   570  	go func() {
   571  		for i := 0; i < niter; i++ {
   572  			v := pn[i%len(pn)]
   573  			expect += v
   574  			q <- v
   575  		}
   576  		close(q)  // no more work
   577  		wg.Wait() // workers done
   578  		close(r)  // ... so there can be no more results
   579  	}()
   580  
   581  	// consume & check
   582  	n := 0
   583  	s := 0
   584  	for v := range r {
   585  		n++
   586  		s += v
   587  	}
   588  	if n != niter || s != expect {
   589  		t.Errorf("Expected sum %d (got %d) from %d iter (saw %d)",
   590  			expect, s, niter, n)
   591  	}
   592  }
   593  
   594  func TestShrinkStackDuringBlockedSend(t *testing.T) {
   595  	// make sure that channel operations still work when we are
   596  	// blocked on a channel send and we shrink the stack.
   597  	// NOTE: this test probably won't fail unless stack1.go:stackDebug
   598  	// is set to >= 1.
   599  	const n = 10
   600  	c := make(chan int)
   601  	done := make(chan struct{})
   602  
   603  	go func() {
   604  		for i := 0; i < n; i++ {
   605  			c <- i
   606  			// use lots of stack, briefly.
   607  			stackGrowthRecursive(20)
   608  		}
   609  		done <- struct{}{}
   610  	}()
   611  
   612  	for i := 0; i < n; i++ {
   613  		x := <-c
   614  		if x != i {
   615  			t.Errorf("bad channel read: want %d, got %d", i, x)
   616  		}
   617  		// Waste some time so sender can finish using lots of stack
   618  		// and block in channel send.
   619  		time.Sleep(1 * time.Millisecond)
   620  		// trigger GC which will shrink the stack of the sender.
   621  		runtime.GC()
   622  	}
   623  	<-done
   624  }
   625  
   626  func TestNoShrinkStackWhileParking(t *testing.T) {
   627  	// The goal of this test is to trigger a "racy sudog adjustment"
   628  	// throw. Basically, there's a window between when a goroutine
   629  	// becomes available for preemption for stack scanning (and thus,
   630  	// stack shrinking) but before the goroutine has fully parked on a
   631  	// channel. See issue 40641 for more details on the problem.
   632  	//
   633  	// The way we try to induce this failure is to set up two
   634  	// goroutines: a sender and a receiver that communicate across
   635  	// a channel. We try to set up a situation where the sender
   636  	// grows its stack temporarily then *fully* blocks on a channel
   637  	// often. Meanwhile a GC is triggered so that we try to get a
   638  	// mark worker to shrink the sender's stack and race with the
   639  	// sender parking.
   640  	//
   641  	// Unfortunately the race window here is so small that we
   642  	// either need a ridiculous number of iterations, or we add
   643  	// "usleep(1000)" to park_m, just before the unlockf call.
   644  	const n = 10
   645  	send := func(c chan<- int, done chan struct{}) {
   646  		for i := 0; i < n; i++ {
   647  			c <- i
   648  			// Use lots of stack briefly so that
   649  			// the GC is going to want to shrink us
   650  			// when it scans us. Make sure not to
   651  			// do any function calls otherwise
   652  			// in order to avoid us shrinking ourselves
   653  			// when we're preempted.
   654  			stackGrowthRecursive(20)
   655  		}
   656  		done <- struct{}{}
   657  	}
   658  	recv := func(c <-chan int, done chan struct{}) {
   659  		for i := 0; i < n; i++ {
   660  			// Sleep here so that the sender always
   661  			// fully blocks.
   662  			time.Sleep(10 * time.Microsecond)
   663  			<-c
   664  		}
   665  		done <- struct{}{}
   666  	}
   667  	for i := 0; i < n*20; i++ {
   668  		c := make(chan int)
   669  		done := make(chan struct{})
   670  		go recv(c, done)
   671  		go send(c, done)
   672  		// Wait a little bit before triggering
   673  		// the GC to make sure the sender and
   674  		// receiver have gotten into their groove.
   675  		time.Sleep(50 * time.Microsecond)
   676  		runtime.GC()
   677  		<-done
   678  		<-done
   679  	}
   680  }
   681  
   682  func TestSelectDuplicateChannel(t *testing.T) {
   683  	// This test makes sure we can queue a G on
   684  	// the same channel multiple times.
   685  	c := make(chan int)
   686  	d := make(chan int)
   687  	e := make(chan int)
   688  
   689  	// goroutine A
   690  	go func() {
   691  		select {
   692  		case <-c:
   693  		case <-c:
   694  		case <-d:
   695  		}
   696  		e <- 9
   697  	}()
   698  	time.Sleep(time.Millisecond) // make sure goroutine A gets queued first on c
   699  
   700  	// goroutine B
   701  	go func() {
   702  		<-c
   703  	}()
   704  	time.Sleep(time.Millisecond) // make sure goroutine B gets queued on c before continuing
   705  
   706  	d <- 7 // wake up A, it dequeues itself from c.  This operation used to corrupt c.recvq.
   707  	<-e    // A tells us it's done
   708  	c <- 8 // wake up B.  This operation used to fail because c.recvq was corrupted (it tries to wake up an already running G instead of B)
   709  }
   710  
   711  func TestSelectStackAdjust(t *testing.T) {
   712  	// Test that channel receive slots that contain local stack
   713  	// pointers are adjusted correctly by stack shrinking.
   714  	c := make(chan *int)
   715  	d := make(chan *int)
   716  	ready1 := make(chan bool)
   717  	ready2 := make(chan bool)
   718  
   719  	f := func(ready chan bool, dup bool) {
   720  		// Temporarily grow the stack to 10K.
   721  		stackGrowthRecursive((10 << 10) / (128 * 8))
   722  
   723  		// We're ready to trigger GC and stack shrink.
   724  		ready <- true
   725  
   726  		val := 42
   727  		var cx *int
   728  		cx = &val
   729  
   730  		var c2 chan *int
   731  		var d2 chan *int
   732  		if dup {
   733  			c2 = c
   734  			d2 = d
   735  		}
   736  
   737  		// Receive from d. cx won't be affected.
   738  		select {
   739  		case cx = <-c:
   740  		case <-c2:
   741  		case <-d:
   742  		case <-d2:
   743  		}
   744  
   745  		// Check that pointer in cx was adjusted correctly.
   746  		if cx != &val {
   747  			t.Error("cx no longer points to val")
   748  		} else if val != 42 {
   749  			t.Error("val changed")
   750  		} else {
   751  			*cx = 43
   752  			if val != 43 {
   753  				t.Error("changing *cx failed to change val")
   754  			}
   755  		}
   756  		ready <- true
   757  	}
   758  
   759  	go f(ready1, false)
   760  	go f(ready2, true)
   761  
   762  	// Let the goroutines get into the select.
   763  	<-ready1
   764  	<-ready2
   765  	time.Sleep(10 * time.Millisecond)
   766  
   767  	// Force concurrent GC to shrink the stacks.
   768  	runtime.GC()
   769  
   770  	// Wake selects.
   771  	close(d)
   772  	<-ready1
   773  	<-ready2
   774  }
   775  
   776  type struct0 struct{}
   777  
   778  func BenchmarkMakeChan(b *testing.B) {
   779  	b.Run("Byte", func(b *testing.B) {
   780  		var x chan byte
   781  		for i := 0; i < b.N; i++ {
   782  			x = make(chan byte, 8)
   783  		}
   784  		close(x)
   785  	})
   786  	b.Run("Int", func(b *testing.B) {
   787  		var x chan int
   788  		for i := 0; i < b.N; i++ {
   789  			x = make(chan int, 8)
   790  		}
   791  		close(x)
   792  	})
   793  	b.Run("Ptr", func(b *testing.B) {
   794  		var x chan *byte
   795  		for i := 0; i < b.N; i++ {
   796  			x = make(chan *byte, 8)
   797  		}
   798  		close(x)
   799  	})
   800  	b.Run("Struct", func(b *testing.B) {
   801  		b.Run("0", func(b *testing.B) {
   802  			var x chan struct0
   803  			for i := 0; i < b.N; i++ {
   804  				x = make(chan struct0, 8)
   805  			}
   806  			close(x)
   807  		})
   808  		b.Run("32", func(b *testing.B) {
   809  			var x chan struct32
   810  			for i := 0; i < b.N; i++ {
   811  				x = make(chan struct32, 8)
   812  			}
   813  			close(x)
   814  		})
   815  		b.Run("40", func(b *testing.B) {
   816  			var x chan struct40
   817  			for i := 0; i < b.N; i++ {
   818  				x = make(chan struct40, 8)
   819  			}
   820  			close(x)
   821  		})
   822  	})
   823  }
   824  
   825  func BenchmarkChanNonblocking(b *testing.B) {
   826  	myc := make(chan int)
   827  	b.RunParallel(func(pb *testing.PB) {
   828  		for pb.Next() {
   829  			select {
   830  			case <-myc:
   831  			default:
   832  			}
   833  		}
   834  	})
   835  }
   836  
   837  func BenchmarkSelectUncontended(b *testing.B) {
   838  	b.RunParallel(func(pb *testing.PB) {
   839  		myc1 := make(chan int, 1)
   840  		myc2 := make(chan int, 1)
   841  		myc1 <- 0
   842  		for pb.Next() {
   843  			select {
   844  			case <-myc1:
   845  				myc2 <- 0
   846  			case <-myc2:
   847  				myc1 <- 0
   848  			}
   849  		}
   850  	})
   851  }
   852  
   853  func BenchmarkSelectSyncContended(b *testing.B) {
   854  	myc1 := make(chan int)
   855  	myc2 := make(chan int)
   856  	myc3 := make(chan int)
   857  	done := make(chan int)
   858  	b.RunParallel(func(pb *testing.PB) {
   859  		go func() {
   860  			for {
   861  				select {
   862  				case myc1 <- 0:
   863  				case myc2 <- 0:
   864  				case myc3 <- 0:
   865  				case <-done:
   866  					return
   867  				}
   868  			}
   869  		}()
   870  		for pb.Next() {
   871  			select {
   872  			case <-myc1:
   873  			case <-myc2:
   874  			case <-myc3:
   875  			}
   876  		}
   877  	})
   878  	close(done)
   879  }
   880  
   881  func BenchmarkSelectAsyncContended(b *testing.B) {
   882  	procs := runtime.GOMAXPROCS(0)
   883  	myc1 := make(chan int, procs)
   884  	myc2 := make(chan int, procs)
   885  	b.RunParallel(func(pb *testing.PB) {
   886  		myc1 <- 0
   887  		for pb.Next() {
   888  			select {
   889  			case <-myc1:
   890  				myc2 <- 0
   891  			case <-myc2:
   892  				myc1 <- 0
   893  			}
   894  		}
   895  	})
   896  }
   897  
   898  func BenchmarkSelectNonblock(b *testing.B) {
   899  	myc1 := make(chan int)
   900  	myc2 := make(chan int)
   901  	myc3 := make(chan int, 1)
   902  	myc4 := make(chan int, 1)
   903  	b.RunParallel(func(pb *testing.PB) {
   904  		for pb.Next() {
   905  			select {
   906  			case <-myc1:
   907  			default:
   908  			}
   909  			select {
   910  			case myc2 <- 0:
   911  			default:
   912  			}
   913  			select {
   914  			case <-myc3:
   915  			default:
   916  			}
   917  			select {
   918  			case myc4 <- 0:
   919  			default:
   920  			}
   921  		}
   922  	})
   923  }
   924  
   925  func BenchmarkChanUncontended(b *testing.B) {
   926  	const C = 100
   927  	b.RunParallel(func(pb *testing.PB) {
   928  		myc := make(chan int, C)
   929  		for pb.Next() {
   930  			for i := 0; i < C; i++ {
   931  				myc <- 0
   932  			}
   933  			for i := 0; i < C; i++ {
   934  				<-myc
   935  			}
   936  		}
   937  	})
   938  }
   939  
   940  func BenchmarkChanContended(b *testing.B) {
   941  	const C = 100
   942  	myc := make(chan int, C*runtime.GOMAXPROCS(0))
   943  	b.RunParallel(func(pb *testing.PB) {
   944  		for pb.Next() {
   945  			for i := 0; i < C; i++ {
   946  				myc <- 0
   947  			}
   948  			for i := 0; i < C; i++ {
   949  				<-myc
   950  			}
   951  		}
   952  	})
   953  }
   954  
   955  func benchmarkChanSync(b *testing.B, work int) {
   956  	const CallsPerSched = 1000
   957  	procs := 2
   958  	N := int32(b.N / CallsPerSched / procs * procs)
   959  	c := make(chan bool, procs)
   960  	myc := make(chan int)
   961  	for p := 0; p < procs; p++ {
   962  		go func() {
   963  			for {
   964  				i := atomic.AddInt32(&N, -1)
   965  				if i < 0 {
   966  					break
   967  				}
   968  				for g := 0; g < CallsPerSched; g++ {
   969  					if i%2 == 0 {
   970  						<-myc
   971  						localWork(work)
   972  						myc <- 0
   973  						localWork(work)
   974  					} else {
   975  						myc <- 0
   976  						localWork(work)
   977  						<-myc
   978  						localWork(work)
   979  					}
   980  				}
   981  			}
   982  			c <- true
   983  		}()
   984  	}
   985  	for p := 0; p < procs; p++ {
   986  		<-c
   987  	}
   988  }
   989  
   990  func BenchmarkChanSync(b *testing.B) {
   991  	benchmarkChanSync(b, 0)
   992  }
   993  
   994  func BenchmarkChanSyncWork(b *testing.B) {
   995  	benchmarkChanSync(b, 1000)
   996  }
   997  
   998  func benchmarkChanProdCons(b *testing.B, chanSize, localWork int) {
   999  	const CallsPerSched = 1000
  1000  	procs := runtime.GOMAXPROCS(-1)
  1001  	N := int32(b.N / CallsPerSched)
  1002  	c := make(chan bool, 2*procs)
  1003  	myc := make(chan int, chanSize)
  1004  	for p := 0; p < procs; p++ {
  1005  		go func() {
  1006  			foo := 0
  1007  			for atomic.AddInt32(&N, -1) >= 0 {
  1008  				for g := 0; g < CallsPerSched; g++ {
  1009  					for i := 0; i < localWork; i++ {
  1010  						foo *= 2
  1011  						foo /= 2
  1012  					}
  1013  					myc <- 1
  1014  				}
  1015  			}
  1016  			myc <- 0
  1017  			c <- foo == 42
  1018  		}()
  1019  		go func() {
  1020  			foo := 0
  1021  			for {
  1022  				v := <-myc
  1023  				if v == 0 {
  1024  					break
  1025  				}
  1026  				for i := 0; i < localWork; i++ {
  1027  					foo *= 2
  1028  					foo /= 2
  1029  				}
  1030  			}
  1031  			c <- foo == 42
  1032  		}()
  1033  	}
  1034  	for p := 0; p < procs; p++ {
  1035  		<-c
  1036  		<-c
  1037  	}
  1038  }
  1039  
  1040  func BenchmarkChanProdCons0(b *testing.B) {
  1041  	benchmarkChanProdCons(b, 0, 0)
  1042  }
  1043  
  1044  func BenchmarkChanProdCons10(b *testing.B) {
  1045  	benchmarkChanProdCons(b, 10, 0)
  1046  }
  1047  
  1048  func BenchmarkChanProdCons100(b *testing.B) {
  1049  	benchmarkChanProdCons(b, 100, 0)
  1050  }
  1051  
  1052  func BenchmarkChanProdConsWork0(b *testing.B) {
  1053  	benchmarkChanProdCons(b, 0, 100)
  1054  }
  1055  
  1056  func BenchmarkChanProdConsWork10(b *testing.B) {
  1057  	benchmarkChanProdCons(b, 10, 100)
  1058  }
  1059  
  1060  func BenchmarkChanProdConsWork100(b *testing.B) {
  1061  	benchmarkChanProdCons(b, 100, 100)
  1062  }
  1063  
  1064  func BenchmarkSelectProdCons(b *testing.B) {
  1065  	const CallsPerSched = 1000
  1066  	procs := runtime.GOMAXPROCS(-1)
  1067  	N := int32(b.N / CallsPerSched)
  1068  	c := make(chan bool, 2*procs)
  1069  	myc := make(chan int, 128)
  1070  	myclose := make(chan bool)
  1071  	for p := 0; p < procs; p++ {
  1072  		go func() {
  1073  			// Producer: sends to myc.
  1074  			foo := 0
  1075  			// Intended to not fire during benchmarking.
  1076  			mytimer := time.After(time.Hour)
  1077  			for atomic.AddInt32(&N, -1) >= 0 {
  1078  				for g := 0; g < CallsPerSched; g++ {
  1079  					// Model some local work.
  1080  					for i := 0; i < 100; i++ {
  1081  						foo *= 2
  1082  						foo /= 2
  1083  					}
  1084  					select {
  1085  					case myc <- 1:
  1086  					case <-mytimer:
  1087  					case <-myclose:
  1088  					}
  1089  				}
  1090  			}
  1091  			myc <- 0
  1092  			c <- foo == 42
  1093  		}()
  1094  		go func() {
  1095  			// Consumer: receives from myc.
  1096  			foo := 0
  1097  			// Intended to not fire during benchmarking.
  1098  			mytimer := time.After(time.Hour)
  1099  		loop:
  1100  			for {
  1101  				select {
  1102  				case v := <-myc:
  1103  					if v == 0 {
  1104  						break loop
  1105  					}
  1106  				case <-mytimer:
  1107  				case <-myclose:
  1108  				}
  1109  				// Model some local work.
  1110  				for i := 0; i < 100; i++ {
  1111  					foo *= 2
  1112  					foo /= 2
  1113  				}
  1114  			}
  1115  			c <- foo == 42
  1116  		}()
  1117  	}
  1118  	for p := 0; p < procs; p++ {
  1119  		<-c
  1120  		<-c
  1121  	}
  1122  }
  1123  
  1124  func BenchmarkChanCreation(b *testing.B) {
  1125  	b.RunParallel(func(pb *testing.PB) {
  1126  		for pb.Next() {
  1127  			myc := make(chan int, 1)
  1128  			myc <- 0
  1129  			<-myc
  1130  		}
  1131  	})
  1132  }
  1133  
  1134  func BenchmarkChanSem(b *testing.B) {
  1135  	type Empty struct{}
  1136  	myc := make(chan Empty, runtime.GOMAXPROCS(0))
  1137  	b.RunParallel(func(pb *testing.PB) {
  1138  		for pb.Next() {
  1139  			myc <- Empty{}
  1140  			<-myc
  1141  		}
  1142  	})
  1143  }
  1144  
  1145  func BenchmarkChanPopular(b *testing.B) {
  1146  	const n = 1000
  1147  	c := make(chan bool)
  1148  	var a []chan bool
  1149  	var wg sync.WaitGroup
  1150  	wg.Add(n)
  1151  	for j := 0; j < n; j++ {
  1152  		d := make(chan bool)
  1153  		a = append(a, d)
  1154  		go func() {
  1155  			for i := 0; i < b.N; i++ {
  1156  				select {
  1157  				case <-c:
  1158  				case <-d:
  1159  				}
  1160  			}
  1161  			wg.Done()
  1162  		}()
  1163  	}
  1164  	for i := 0; i < b.N; i++ {
  1165  		for _, d := range a {
  1166  			d <- true
  1167  		}
  1168  	}
  1169  	wg.Wait()
  1170  }
  1171  
  1172  func BenchmarkChanClosed(b *testing.B) {
  1173  	c := make(chan struct{})
  1174  	close(c)
  1175  	b.RunParallel(func(pb *testing.PB) {
  1176  		for pb.Next() {
  1177  			select {
  1178  			case <-c:
  1179  			default:
  1180  				b.Error("Unreachable")
  1181  			}
  1182  		}
  1183  	})
  1184  }
  1185  
  1186  var (
  1187  	alwaysFalse = false
  1188  	workSink    = 0
  1189  )
  1190  
  1191  func localWork(w int) {
  1192  	foo := 0
  1193  	for i := 0; i < w; i++ {
  1194  		foo /= (foo + 1)
  1195  	}
  1196  	if alwaysFalse {
  1197  		workSink += foo
  1198  	}
  1199  }
  1200  

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