...
Run Format

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 five nines is 4.4172 / (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 > 4.4172/(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 TestSelectDuplicateChannel(t *testing.T) {
   627  	// This test makes sure we can queue a G on
   628  	// the same channel multiple times.
   629  	c := make(chan int)
   630  	d := make(chan int)
   631  	e := make(chan int)
   632  
   633  	// goroutine A
   634  	go func() {
   635  		select {
   636  		case <-c:
   637  		case <-c:
   638  		case <-d:
   639  		}
   640  		e <- 9
   641  	}()
   642  	time.Sleep(time.Millisecond) // make sure goroutine A gets queued first on c
   643  
   644  	// goroutine B
   645  	go func() {
   646  		<-c
   647  	}()
   648  	time.Sleep(time.Millisecond) // make sure goroutine B gets queued on c before continuing
   649  
   650  	d <- 7 // wake up A, it dequeues itself from c.  This operation used to corrupt c.recvq.
   651  	<-e    // A tells us it's done
   652  	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)
   653  }
   654  
   655  var selectSink interface{}
   656  
   657  func TestSelectStackAdjust(t *testing.T) {
   658  	// Test that channel receive slots that contain local stack
   659  	// pointers are adjusted correctly by stack shrinking.
   660  	c := make(chan *int)
   661  	d := make(chan *int)
   662  	ready1 := make(chan bool)
   663  	ready2 := make(chan bool)
   664  
   665  	f := func(ready chan bool, dup bool) {
   666  		// Temporarily grow the stack to 10K.
   667  		stackGrowthRecursive((10 << 10) / (128 * 8))
   668  
   669  		// We're ready to trigger GC and stack shrink.
   670  		ready <- true
   671  
   672  		val := 42
   673  		var cx *int
   674  		cx = &val
   675  
   676  		var c2 chan *int
   677  		var d2 chan *int
   678  		if dup {
   679  			c2 = c
   680  			d2 = d
   681  		}
   682  
   683  		// Receive from d. cx won't be affected.
   684  		select {
   685  		case cx = <-c:
   686  		case <-c2:
   687  		case <-d:
   688  		case <-d2:
   689  		}
   690  
   691  		// Check that pointer in cx was adjusted correctly.
   692  		if cx != &val {
   693  			t.Error("cx no longer points to val")
   694  		} else if val != 42 {
   695  			t.Error("val changed")
   696  		} else {
   697  			*cx = 43
   698  			if val != 43 {
   699  				t.Error("changing *cx failed to change val")
   700  			}
   701  		}
   702  		ready <- true
   703  	}
   704  
   705  	go f(ready1, false)
   706  	go f(ready2, true)
   707  
   708  	// Let the goroutines get into the select.
   709  	<-ready1
   710  	<-ready2
   711  	time.Sleep(10 * time.Millisecond)
   712  
   713  	// Force concurrent GC a few times.
   714  	var before, after runtime.MemStats
   715  	runtime.ReadMemStats(&before)
   716  	for i := 0; i < 100; i++ {
   717  		selectSink = new([1 << 20]byte)
   718  		runtime.ReadMemStats(&after)
   719  		if after.NumGC-before.NumGC >= 2 {
   720  			goto done
   721  		}
   722  	}
   723  	t.Fatal("failed to trigger concurrent GC")
   724  done:
   725  	selectSink = nil
   726  
   727  	// Wake selects.
   728  	close(d)
   729  	<-ready1
   730  	<-ready2
   731  }
   732  
   733  type struct0 struct{}
   734  
   735  func BenchmarkMakeChan(b *testing.B) {
   736  	b.Run("Byte", func(b *testing.B) {
   737  		var x chan byte
   738  		for i := 0; i < b.N; i++ {
   739  			x = make(chan byte, 8)
   740  		}
   741  		close(x)
   742  	})
   743  	b.Run("Int", func(b *testing.B) {
   744  		var x chan int
   745  		for i := 0; i < b.N; i++ {
   746  			x = make(chan int, 8)
   747  		}
   748  		close(x)
   749  	})
   750  	b.Run("Ptr", func(b *testing.B) {
   751  		var x chan *byte
   752  		for i := 0; i < b.N; i++ {
   753  			x = make(chan *byte, 8)
   754  		}
   755  		close(x)
   756  	})
   757  	b.Run("Struct", func(b *testing.B) {
   758  		b.Run("0", func(b *testing.B) {
   759  			var x chan struct0
   760  			for i := 0; i < b.N; i++ {
   761  				x = make(chan struct0, 8)
   762  			}
   763  			close(x)
   764  		})
   765  		b.Run("32", func(b *testing.B) {
   766  			var x chan struct32
   767  			for i := 0; i < b.N; i++ {
   768  				x = make(chan struct32, 8)
   769  			}
   770  			close(x)
   771  		})
   772  		b.Run("40", func(b *testing.B) {
   773  			var x chan struct40
   774  			for i := 0; i < b.N; i++ {
   775  				x = make(chan struct40, 8)
   776  			}
   777  			close(x)
   778  		})
   779  	})
   780  }
   781  
   782  func BenchmarkChanNonblocking(b *testing.B) {
   783  	myc := make(chan int)
   784  	b.RunParallel(func(pb *testing.PB) {
   785  		for pb.Next() {
   786  			select {
   787  			case <-myc:
   788  			default:
   789  			}
   790  		}
   791  	})
   792  }
   793  
   794  func BenchmarkSelectUncontended(b *testing.B) {
   795  	b.RunParallel(func(pb *testing.PB) {
   796  		myc1 := make(chan int, 1)
   797  		myc2 := make(chan int, 1)
   798  		myc1 <- 0
   799  		for pb.Next() {
   800  			select {
   801  			case <-myc1:
   802  				myc2 <- 0
   803  			case <-myc2:
   804  				myc1 <- 0
   805  			}
   806  		}
   807  	})
   808  }
   809  
   810  func BenchmarkSelectSyncContended(b *testing.B) {
   811  	myc1 := make(chan int)
   812  	myc2 := make(chan int)
   813  	myc3 := make(chan int)
   814  	done := make(chan int)
   815  	b.RunParallel(func(pb *testing.PB) {
   816  		go func() {
   817  			for {
   818  				select {
   819  				case myc1 <- 0:
   820  				case myc2 <- 0:
   821  				case myc3 <- 0:
   822  				case <-done:
   823  					return
   824  				}
   825  			}
   826  		}()
   827  		for pb.Next() {
   828  			select {
   829  			case <-myc1:
   830  			case <-myc2:
   831  			case <-myc3:
   832  			}
   833  		}
   834  	})
   835  	close(done)
   836  }
   837  
   838  func BenchmarkSelectAsyncContended(b *testing.B) {
   839  	procs := runtime.GOMAXPROCS(0)
   840  	myc1 := make(chan int, procs)
   841  	myc2 := make(chan int, procs)
   842  	b.RunParallel(func(pb *testing.PB) {
   843  		myc1 <- 0
   844  		for pb.Next() {
   845  			select {
   846  			case <-myc1:
   847  				myc2 <- 0
   848  			case <-myc2:
   849  				myc1 <- 0
   850  			}
   851  		}
   852  	})
   853  }
   854  
   855  func BenchmarkSelectNonblock(b *testing.B) {
   856  	myc1 := make(chan int)
   857  	myc2 := make(chan int)
   858  	myc3 := make(chan int, 1)
   859  	myc4 := make(chan int, 1)
   860  	b.RunParallel(func(pb *testing.PB) {
   861  		for pb.Next() {
   862  			select {
   863  			case <-myc1:
   864  			default:
   865  			}
   866  			select {
   867  			case myc2 <- 0:
   868  			default:
   869  			}
   870  			select {
   871  			case <-myc3:
   872  			default:
   873  			}
   874  			select {
   875  			case myc4 <- 0:
   876  			default:
   877  			}
   878  		}
   879  	})
   880  }
   881  
   882  func BenchmarkChanUncontended(b *testing.B) {
   883  	const C = 100
   884  	b.RunParallel(func(pb *testing.PB) {
   885  		myc := make(chan int, C)
   886  		for pb.Next() {
   887  			for i := 0; i < C; i++ {
   888  				myc <- 0
   889  			}
   890  			for i := 0; i < C; i++ {
   891  				<-myc
   892  			}
   893  		}
   894  	})
   895  }
   896  
   897  func BenchmarkChanContended(b *testing.B) {
   898  	const C = 100
   899  	myc := make(chan int, C*runtime.GOMAXPROCS(0))
   900  	b.RunParallel(func(pb *testing.PB) {
   901  		for pb.Next() {
   902  			for i := 0; i < C; i++ {
   903  				myc <- 0
   904  			}
   905  			for i := 0; i < C; i++ {
   906  				<-myc
   907  			}
   908  		}
   909  	})
   910  }
   911  
   912  func benchmarkChanSync(b *testing.B, work int) {
   913  	const CallsPerSched = 1000
   914  	procs := 2
   915  	N := int32(b.N / CallsPerSched / procs * procs)
   916  	c := make(chan bool, procs)
   917  	myc := make(chan int)
   918  	for p := 0; p < procs; p++ {
   919  		go func() {
   920  			for {
   921  				i := atomic.AddInt32(&N, -1)
   922  				if i < 0 {
   923  					break
   924  				}
   925  				for g := 0; g < CallsPerSched; g++ {
   926  					if i%2 == 0 {
   927  						<-myc
   928  						localWork(work)
   929  						myc <- 0
   930  						localWork(work)
   931  					} else {
   932  						myc <- 0
   933  						localWork(work)
   934  						<-myc
   935  						localWork(work)
   936  					}
   937  				}
   938  			}
   939  			c <- true
   940  		}()
   941  	}
   942  	for p := 0; p < procs; p++ {
   943  		<-c
   944  	}
   945  }
   946  
   947  func BenchmarkChanSync(b *testing.B) {
   948  	benchmarkChanSync(b, 0)
   949  }
   950  
   951  func BenchmarkChanSyncWork(b *testing.B) {
   952  	benchmarkChanSync(b, 1000)
   953  }
   954  
   955  func benchmarkChanProdCons(b *testing.B, chanSize, localWork int) {
   956  	const CallsPerSched = 1000
   957  	procs := runtime.GOMAXPROCS(-1)
   958  	N := int32(b.N / CallsPerSched)
   959  	c := make(chan bool, 2*procs)
   960  	myc := make(chan int, chanSize)
   961  	for p := 0; p < procs; p++ {
   962  		go func() {
   963  			foo := 0
   964  			for atomic.AddInt32(&N, -1) >= 0 {
   965  				for g := 0; g < CallsPerSched; g++ {
   966  					for i := 0; i < localWork; i++ {
   967  						foo *= 2
   968  						foo /= 2
   969  					}
   970  					myc <- 1
   971  				}
   972  			}
   973  			myc <- 0
   974  			c <- foo == 42
   975  		}()
   976  		go func() {
   977  			foo := 0
   978  			for {
   979  				v := <-myc
   980  				if v == 0 {
   981  					break
   982  				}
   983  				for i := 0; i < localWork; i++ {
   984  					foo *= 2
   985  					foo /= 2
   986  				}
   987  			}
   988  			c <- foo == 42
   989  		}()
   990  	}
   991  	for p := 0; p < procs; p++ {
   992  		<-c
   993  		<-c
   994  	}
   995  }
   996  
   997  func BenchmarkChanProdCons0(b *testing.B) {
   998  	benchmarkChanProdCons(b, 0, 0)
   999  }
  1000  
  1001  func BenchmarkChanProdCons10(b *testing.B) {
  1002  	benchmarkChanProdCons(b, 10, 0)
  1003  }
  1004  
  1005  func BenchmarkChanProdCons100(b *testing.B) {
  1006  	benchmarkChanProdCons(b, 100, 0)
  1007  }
  1008  
  1009  func BenchmarkChanProdConsWork0(b *testing.B) {
  1010  	benchmarkChanProdCons(b, 0, 100)
  1011  }
  1012  
  1013  func BenchmarkChanProdConsWork10(b *testing.B) {
  1014  	benchmarkChanProdCons(b, 10, 100)
  1015  }
  1016  
  1017  func BenchmarkChanProdConsWork100(b *testing.B) {
  1018  	benchmarkChanProdCons(b, 100, 100)
  1019  }
  1020  
  1021  func BenchmarkSelectProdCons(b *testing.B) {
  1022  	const CallsPerSched = 1000
  1023  	procs := runtime.GOMAXPROCS(-1)
  1024  	N := int32(b.N / CallsPerSched)
  1025  	c := make(chan bool, 2*procs)
  1026  	myc := make(chan int, 128)
  1027  	myclose := make(chan bool)
  1028  	for p := 0; p < procs; p++ {
  1029  		go func() {
  1030  			// Producer: sends to myc.
  1031  			foo := 0
  1032  			// Intended to not fire during benchmarking.
  1033  			mytimer := time.After(time.Hour)
  1034  			for atomic.AddInt32(&N, -1) >= 0 {
  1035  				for g := 0; g < CallsPerSched; g++ {
  1036  					// Model some local work.
  1037  					for i := 0; i < 100; i++ {
  1038  						foo *= 2
  1039  						foo /= 2
  1040  					}
  1041  					select {
  1042  					case myc <- 1:
  1043  					case <-mytimer:
  1044  					case <-myclose:
  1045  					}
  1046  				}
  1047  			}
  1048  			myc <- 0
  1049  			c <- foo == 42
  1050  		}()
  1051  		go func() {
  1052  			// Consumer: receives from myc.
  1053  			foo := 0
  1054  			// Intended to not fire during benchmarking.
  1055  			mytimer := time.After(time.Hour)
  1056  		loop:
  1057  			for {
  1058  				select {
  1059  				case v := <-myc:
  1060  					if v == 0 {
  1061  						break loop
  1062  					}
  1063  				case <-mytimer:
  1064  				case <-myclose:
  1065  				}
  1066  				// Model some local work.
  1067  				for i := 0; i < 100; i++ {
  1068  					foo *= 2
  1069  					foo /= 2
  1070  				}
  1071  			}
  1072  			c <- foo == 42
  1073  		}()
  1074  	}
  1075  	for p := 0; p < procs; p++ {
  1076  		<-c
  1077  		<-c
  1078  	}
  1079  }
  1080  
  1081  func BenchmarkChanCreation(b *testing.B) {
  1082  	b.RunParallel(func(pb *testing.PB) {
  1083  		for pb.Next() {
  1084  			myc := make(chan int, 1)
  1085  			myc <- 0
  1086  			<-myc
  1087  		}
  1088  	})
  1089  }
  1090  
  1091  func BenchmarkChanSem(b *testing.B) {
  1092  	type Empty struct{}
  1093  	myc := make(chan Empty, runtime.GOMAXPROCS(0))
  1094  	b.RunParallel(func(pb *testing.PB) {
  1095  		for pb.Next() {
  1096  			myc <- Empty{}
  1097  			<-myc
  1098  		}
  1099  	})
  1100  }
  1101  
  1102  func BenchmarkChanPopular(b *testing.B) {
  1103  	const n = 1000
  1104  	c := make(chan bool)
  1105  	var a []chan bool
  1106  	var wg sync.WaitGroup
  1107  	wg.Add(n)
  1108  	for j := 0; j < n; j++ {
  1109  		d := make(chan bool)
  1110  		a = append(a, d)
  1111  		go func() {
  1112  			for i := 0; i < b.N; i++ {
  1113  				select {
  1114  				case <-c:
  1115  				case <-d:
  1116  				}
  1117  			}
  1118  			wg.Done()
  1119  		}()
  1120  	}
  1121  	for i := 0; i < b.N; i++ {
  1122  		for _, d := range a {
  1123  			d <- true
  1124  		}
  1125  	}
  1126  	wg.Wait()
  1127  }
  1128  
  1129  var (
  1130  	alwaysFalse = false
  1131  	workSink    = 0
  1132  )
  1133  
  1134  func localWork(w int) {
  1135  	foo := 0
  1136  	for i := 0; i < w; i++ {
  1137  		foo /= (foo + 1)
  1138  	}
  1139  	if alwaysFalse {
  1140  		workSink += foo
  1141  	}
  1142  }
  1143  

View as plain text