reflect: add Select
R=r, iant, rogpeppe, bradfitz
CC=golang-dev
https://golang.org/cl/6498078
diff --git a/src/pkg/reflect/all_test.go b/src/pkg/reflect/all_test.go
index ad7e134..fe16087 100644
--- a/src/pkg/reflect/all_test.go
+++ b/src/pkg/reflect/all_test.go
@@ -9,10 +9,13 @@
"encoding/base64"
"fmt"
"io"
+ "math/rand"
"os"
. "reflect"
"runtime"
+ "sync"
"testing"
+ "time"
"unsafe"
)
@@ -1055,6 +1058,336 @@
}
}
+// caseInfo describes a single case in a select test.
+type caseInfo struct {
+ desc string
+ canSelect bool
+ recv Value
+ closed bool
+ helper func()
+ panic bool
+}
+
+func TestSelect(t *testing.T) {
+ selectWatch.once.Do(func() { go selectWatcher() })
+
+ var x exhaustive
+ nch := 0
+ newop := func(n int, cap int) (ch, val Value) {
+ nch++
+ if nch%101%2 == 1 {
+ c := make(chan int, cap)
+ ch = ValueOf(c)
+ val = ValueOf(n)
+ } else {
+ c := make(chan string, cap)
+ ch = ValueOf(c)
+ val = ValueOf(fmt.Sprint(n))
+ }
+ return
+ }
+
+ for n := 0; x.Next(); n++ {
+ if testing.Short() && n >= 1000 {
+ break
+ }
+ if n%100000 == 0 && testing.Verbose() {
+ println("TestSelect", n)
+ }
+ var cases []SelectCase
+ var info []caseInfo
+
+ // Ready send.
+ if x.Maybe() {
+ ch, val := newop(len(cases), 1)
+ cases = append(cases, SelectCase{
+ Dir: SelectSend,
+ Chan: ch,
+ Send: val,
+ })
+ info = append(info, caseInfo{desc: "ready send", canSelect: true})
+ }
+
+ // Ready recv.
+ if x.Maybe() {
+ ch, val := newop(len(cases), 1)
+ ch.Send(val)
+ cases = append(cases, SelectCase{
+ Dir: SelectRecv,
+ Chan: ch,
+ })
+ info = append(info, caseInfo{desc: "ready recv", canSelect: true, recv: val})
+ }
+
+ // Blocking send.
+ if x.Maybe() {
+ ch, val := newop(len(cases), 0)
+ cases = append(cases, SelectCase{
+ Dir: SelectSend,
+ Chan: ch,
+ Send: val,
+ })
+ // Let it execute?
+ if x.Maybe() {
+ f := func() { ch.Recv() }
+ info = append(info, caseInfo{desc: "blocking send", helper: f})
+ } else {
+ info = append(info, caseInfo{desc: "blocking send"})
+ }
+ }
+
+ // Blocking recv.
+ if x.Maybe() {
+ ch, val := newop(len(cases), 0)
+ cases = append(cases, SelectCase{
+ Dir: SelectRecv,
+ Chan: ch,
+ })
+ // Let it execute?
+ if x.Maybe() {
+ f := func() { ch.Send(val) }
+ info = append(info, caseInfo{desc: "blocking recv", recv: val, helper: f})
+ } else {
+ info = append(info, caseInfo{desc: "blocking recv"})
+ }
+ }
+
+ // Zero Chan send.
+ if x.Maybe() {
+ // Maybe include value to send.
+ var val Value
+ if x.Maybe() {
+ val = ValueOf(100)
+ }
+ cases = append(cases, SelectCase{
+ Dir: SelectSend,
+ Send: val,
+ })
+ info = append(info, caseInfo{desc: "zero Chan send"})
+ }
+
+ // Zero Chan receive.
+ if x.Maybe() {
+ cases = append(cases, SelectCase{
+ Dir: SelectRecv,
+ })
+ info = append(info, caseInfo{desc: "zero Chan recv"})
+ }
+
+ // nil Chan send.
+ if x.Maybe() {
+ cases = append(cases, SelectCase{
+ Dir: SelectSend,
+ Chan: ValueOf((chan int)(nil)),
+ Send: ValueOf(101),
+ })
+ info = append(info, caseInfo{desc: "nil Chan send"})
+ }
+
+ // nil Chan recv.
+ if x.Maybe() {
+ cases = append(cases, SelectCase{
+ Dir: SelectRecv,
+ Chan: ValueOf((chan int)(nil)),
+ })
+ info = append(info, caseInfo{desc: "nil Chan recv"})
+ }
+
+ // closed Chan send.
+ if x.Maybe() {
+ ch := make(chan int)
+ close(ch)
+ cases = append(cases, SelectCase{
+ Dir: SelectSend,
+ Chan: ValueOf(ch),
+ Send: ValueOf(101),
+ })
+ info = append(info, caseInfo{desc: "closed Chan send", canSelect: true, panic: true})
+ }
+
+ // closed Chan recv.
+ if x.Maybe() {
+ ch, val := newop(len(cases), 0)
+ ch.Close()
+ val = Zero(val.Type())
+ cases = append(cases, SelectCase{
+ Dir: SelectRecv,
+ Chan: ch,
+ })
+ info = append(info, caseInfo{desc: "closed Chan recv", canSelect: true, closed: true, recv: val})
+ }
+
+ var helper func() // goroutine to help the select complete
+
+ // Add default? Must be last case here, but will permute.
+ // Add the default if the select would otherwise
+ // block forever, and maybe add it anyway.
+ numCanSelect := 0
+ canProceed := false
+ canBlock := true
+ canPanic := false
+ helpers := []int{}
+ for i, c := range info {
+ if c.canSelect {
+ canProceed = true
+ canBlock = false
+ numCanSelect++
+ if c.panic {
+ canPanic = true
+ }
+ } else if c.helper != nil {
+ canProceed = true
+ helpers = append(helpers, i)
+ }
+ }
+ if !canProceed || x.Maybe() {
+ cases = append(cases, SelectCase{
+ Dir: SelectDefault,
+ })
+ info = append(info, caseInfo{desc: "default", canSelect: canBlock})
+ numCanSelect++
+ } else if canBlock {
+ // Select needs to communicate with another goroutine.
+ cas := &info[helpers[x.Choose(len(helpers))]]
+ helper = cas.helper
+ cas.canSelect = true
+ numCanSelect++
+ }
+
+ // Permute cases and case info.
+ // Doing too much here makes the exhaustive loop
+ // too exhausting, so just do two swaps.
+ for loop := 0; loop < 2; loop++ {
+ i := x.Choose(len(cases))
+ j := x.Choose(len(cases))
+ cases[i], cases[j] = cases[j], cases[i]
+ info[i], info[j] = info[j], info[i]
+ }
+
+ if helper != nil {
+ // We wait before kicking off a goroutine to satisfy a blocked select.
+ // The pause needs to be big enough to let the select block before
+ // we run the helper, but if we lose that race once in a while it's okay: the
+ // select will just proceed immediately. Not a big deal.
+ // For short tests we can grow [sic] the timeout a bit without fear of taking too long
+ pause := 10 * time.Microsecond
+ if testing.Short() {
+ pause = 100 * time.Microsecond
+ }
+ time.AfterFunc(pause, helper)
+ }
+
+ // Run select.
+ i, recv, recvOK, panicErr := runSelect(cases, info)
+ if panicErr != nil && !canPanic {
+ t.Fatalf("%s\npanicked unexpectedly: %v", fmtSelect(info), panicErr)
+ }
+ if panicErr == nil && canPanic && numCanSelect == 1 {
+ t.Fatalf("%s\nselected #%d incorrectly (should panic)", fmtSelect(info), i)
+ }
+ if panicErr != nil {
+ continue
+ }
+
+ cas := info[i]
+ if !cas.canSelect {
+ recvStr := ""
+ if recv.IsValid() {
+ recvStr = fmt.Sprintf(", received %v, %v", recv.Interface(), recvOK)
+ }
+ t.Fatalf("%s\nselected #%d incorrectly%s", fmtSelect(info), i, recvStr)
+ continue
+ }
+ if cas.panic {
+ t.Fatalf("%s\nselected #%d incorrectly (case should panic)", fmtSelect(info), i)
+ continue
+ }
+
+ if cases[i].Dir == SelectRecv {
+ if !recv.IsValid() {
+ t.Fatalf("%s\nselected #%d but got %v, %v, want %v, %v", fmtSelect(info), i, recv, recvOK, cas.recv.Interface(), !cas.closed)
+ }
+ if !cas.recv.IsValid() {
+ t.Fatalf("%s\nselected #%d but internal error: missing recv value", fmtSelect(info), i)
+ }
+ if recv.Interface() != cas.recv.Interface() || recvOK != !cas.closed {
+ if recv.Interface() == cas.recv.Interface() && recvOK == !cas.closed {
+ t.Fatalf("%s\nselected #%d, got %#v, %v, and DeepEqual is broken on %T", fmtSelect(info), i, recv.Interface(), recvOK, recv.Interface())
+ }
+ t.Fatalf("%s\nselected #%d but got %#v, %v, want %#v, %v", fmtSelect(info), i, recv.Interface(), recvOK, cas.recv.Interface(), !cas.closed)
+ }
+ } else {
+ if recv.IsValid() || recvOK {
+ t.Fatalf("%s\nselected #%d but got %v, %v, want %v, %v", fmtSelect(info), i, recv, recvOK, Value{}, false)
+ }
+ }
+ }
+}
+
+// selectWatch and the selectWatcher are a watchdog mechanism for running Select.
+// If the selectWatcher notices that the select has been blocked for >1 second, it prints
+// an error describing the select and panics the entire test binary.
+var selectWatch struct {
+ sync.Mutex
+ once sync.Once
+ now time.Time
+ info []caseInfo
+}
+
+func selectWatcher() {
+ for {
+ time.Sleep(1 * time.Second)
+ selectWatch.Lock()
+ if selectWatch.info != nil && time.Since(selectWatch.now) > 1*time.Second {
+ fmt.Fprintf(os.Stderr, "TestSelect:\n%s blocked indefinitely\n", fmtSelect(selectWatch.info))
+ panic("select stuck")
+ }
+ selectWatch.Unlock()
+ }
+}
+
+// runSelect runs a single select test.
+// It returns the values returned by Select but also returns
+// a panic value if the Select panics.
+func runSelect(cases []SelectCase, info []caseInfo) (chosen int, recv Value, recvOK bool, panicErr interface{}) {
+ defer func() {
+ panicErr = recover()
+
+ selectWatch.Lock()
+ selectWatch.info = nil
+ selectWatch.Unlock()
+ }()
+
+ selectWatch.Lock()
+ selectWatch.now = time.Now()
+ selectWatch.info = info
+ selectWatch.Unlock()
+
+ chosen, recv, recvOK = Select(cases)
+ return
+}
+
+// fmtSelect formats the information about a single select test.
+func fmtSelect(info []caseInfo) string {
+ var buf bytes.Buffer
+ fmt.Fprintf(&buf, "\nselect {\n")
+ for i, cas := range info {
+ fmt.Fprintf(&buf, "%d: %s", i, cas.desc)
+ if cas.recv.IsValid() {
+ fmt.Fprintf(&buf, " val=%#v", cas.recv.Interface())
+ }
+ if cas.canSelect {
+ fmt.Fprintf(&buf, " canselect")
+ }
+ if cas.panic {
+ fmt.Fprintf(&buf, " panic")
+ }
+ fmt.Fprintf(&buf, "\n")
+ }
+ fmt.Fprintf(&buf, "}")
+ return buf.String()
+}
+
// Difficult test for function call because of
// implicit padding between arguments.
func dummy(b byte, c int, d byte) (i byte, j int, k byte) {
@@ -1933,3 +2266,94 @@
t.FieldByName("X")
}
}
+
+// An exhaustive is a mechanism for writing exhaustive or stochastic tests.
+// The basic usage is:
+//
+// for x.Next() {
+// ... code using x.Maybe() or x.Choice(n) to create test cases ...
+// }
+//
+// Each iteration of the loop returns a different set of results, until all
+// possible result sets have been explored. It is okay for different code paths
+// to make different method call sequences on x, but there must be no
+// other source of non-determinism in the call sequences.
+//
+// When faced with a new decision, x chooses randomly. Future explorations
+// of that path will choose successive values for the result. Thus, stopping
+// the loop after a fixed number of iterations gives somewhat stochastic
+// testing.
+//
+// Example:
+//
+// for x.Next() {
+// v := make([]bool, x.Choose(4))
+// for i := range v {
+// v[i] = x.Maybe()
+// }
+// fmt.Println(v)
+// }
+//
+// prints (in some order):
+//
+// []
+// [false]
+// [true]
+// [false false]
+// [false true]
+// ...
+// [true true]
+// [false false false]
+// ...
+// [true true true]
+// [false false false false]
+// ...
+// [true true true true]
+//
+type exhaustive struct {
+ r *rand.Rand
+ pos int
+ last []choice
+}
+
+type choice struct {
+ off int
+ n int
+ max int
+}
+
+func (x *exhaustive) Next() bool {
+ if x.r == nil {
+ x.r = rand.New(rand.NewSource(time.Now().UnixNano()))
+ }
+ x.pos = 0
+ if x.last == nil {
+ x.last = []choice{}
+ return true
+ }
+ for i := len(x.last) - 1; i >= 0; i-- {
+ c := &x.last[i]
+ if c.n+1 < c.max {
+ c.n++
+ x.last = x.last[:i+1]
+ return true
+ }
+ }
+ return false
+}
+
+func (x *exhaustive) Choose(max int) int {
+ if x.pos >= len(x.last) {
+ x.last = append(x.last, choice{x.r.Intn(max), 0, max})
+ }
+ c := &x.last[x.pos]
+ x.pos++
+ if c.max != max {
+ panic("inconsistent use of exhaustive tester")
+ }
+ return (c.n + c.off) % max
+}
+
+func (x *exhaustive) Maybe() bool {
+ return x.Choose(2) == 1
+}
diff --git a/src/pkg/reflect/type.go b/src/pkg/reflect/type.go
index 52eac22..dfbd859 100644
--- a/src/pkg/reflect/type.go
+++ b/src/pkg/reflect/type.go
@@ -186,6 +186,12 @@
uncommon() *uncommonType
}
+/*
+ * These data structures are known to the compiler (../../cmd/gc/reflect.c).
+ * A few are known to ../runtime/type.go to convey to debuggers.
+ * They are also known to ../runtime/type.h.
+ */
+
// A Kind represents the specific kind of type that a Type represents.
// The zero Kind is not a valid kind.
type Kind uint
@@ -220,11 +226,6 @@
UnsafePointer
)
-/*
- * These data structures are known to the compiler (../../cmd/gc/reflect.c).
- * A few are known to ../runtime/type.go to convey to debuggers.
- */
-
// The compiler can only construct empty interface values at
// compile time; non-empty interface values get created
// during initialization. Type is an empty interface
diff --git a/src/pkg/reflect/value.go b/src/pkg/reflect/value.go
index c44d408..9b01646 100644
--- a/src/pkg/reflect/value.go
+++ b/src/pkg/reflect/value.go
@@ -1618,6 +1618,140 @@
return n
}
+// A runtimeSelect is a single case passed to rselect.
+// This must match ../runtime/chan.c:/runtimeSelect
+type runtimeSelect struct {
+ dir uintptr // 0, SendDir, or RecvDir
+ typ *runtimeType // channel type
+ ch iword // interface word for channel
+ val iword // interface word for value (for SendDir)
+}
+
+// rselect runs a select. It returns the index of the chosen case,
+// and if the case was a receive, the interface word of the received
+// value and the conventional OK bool to indicate whether the receive
+// corresponds to a sent value.
+func rselect([]runtimeSelect) (chosen int, recv iword, recvOK bool)
+
+// A SelectDir describes the communication direction of a select case.
+type SelectDir int
+
+// NOTE: These values must match ../runtime/chan.c:/SelectDir.
+
+const (
+ _ SelectDir = iota
+ SelectSend // case Chan <- Send
+ SelectRecv // case <-Chan:
+ SelectDefault // default
+)
+
+// A SelectCase describes a single case in a select operation.
+// The kind of case depends on Dir, the communication direction.
+//
+// If Dir is SelectDefault, the case represents a default case.
+// Chan and Send must be zero Values.
+//
+// If Dir is SelectSend, the case represents a send operation.
+// Normally Chan's underlying value must be a channel, and Send's underlying value must be
+// assignable to the channel's element type. As a special case, if Chan is a zero Value,
+// then the case is ignored, and the field Send will also be ignored and may be either zero
+// or non-zero.
+//
+// If Dir is SelectRecv, the case represents a receive operation.
+// Normally Chan's underlying value must be a channel and Send must be a zero Value.
+// If Chan is a zero Value, then the case is ignored, but Send must still be a zero Value.
+// When a receive operation is selected, the received Value is returned by Select.
+//
+type SelectCase struct {
+ Dir SelectDir // direction of case
+ Chan Value // channel to use (for send or receive)
+ Send Value // value to send (for send)
+}
+
+// Select executes a select operation described by the list of cases.
+// Like the Go select statement, it blocks until one of the cases can
+// proceed and then executes that case. It returns the index of the chosen case
+// and, if that case was a receive operation, the value received and a
+// boolean indicating whether the value corresponds to a send on the channel
+// (as opposed to a zero value received because the channel is closed).
+func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool) {
+ // NOTE: Do not trust that caller is not modifying cases data underfoot.
+ // The range is safe because the caller cannot modify our copy of the len
+ // and each iteration makes its own copy of the value c.
+ runcases := make([]runtimeSelect, len(cases))
+ haveDefault := false
+ for i, c := range cases {
+ rc := &runcases[i]
+ rc.dir = uintptr(c.Dir)
+ switch c.Dir {
+ default:
+ panic("reflect.Select: invalid Dir")
+
+ case SelectDefault: // default
+ if haveDefault {
+ panic("reflect.Select: multiple default cases")
+ }
+ haveDefault = true
+ if c.Chan.IsValid() {
+ panic("reflect.Select: default case has Chan value")
+ }
+ if c.Send.IsValid() {
+ panic("reflect.Select: default case has Send value")
+ }
+
+ case SelectSend:
+ ch := c.Chan
+ if !ch.IsValid() {
+ break
+ }
+ ch.mustBe(Chan)
+ ch.mustBeExported()
+ tt := (*chanType)(unsafe.Pointer(ch.typ))
+ if ChanDir(tt.dir)&SendDir == 0 {
+ panic("reflect.Select: SendDir case using recv-only channel")
+ }
+ rc.ch = ch.iword()
+ rc.typ = tt.runtimeType()
+ v := c.Send
+ if !v.IsValid() {
+ panic("reflect.Select: SendDir case missing Send value")
+ }
+ v.mustBeExported()
+ v = v.assignTo("reflect.Select", toCommonType(tt.elem), nil)
+ rc.val = v.iword()
+
+ case SelectRecv:
+ if c.Send.IsValid() {
+ panic("reflect.Select: RecvDir case has Send value")
+ }
+ ch := c.Chan
+ if !ch.IsValid() {
+ break
+ }
+ ch.mustBe(Chan)
+ ch.mustBeExported()
+ tt := (*chanType)(unsafe.Pointer(ch.typ))
+ rc.typ = tt.runtimeType()
+ if ChanDir(tt.dir)&RecvDir == 0 {
+ panic("reflect.Select: RecvDir case using send-only channel")
+ }
+ rc.ch = ch.iword()
+ }
+ }
+
+ chosen, word, recvOK := rselect(runcases)
+ if runcases[chosen].dir == uintptr(SelectRecv) {
+ tt := (*chanType)(unsafe.Pointer(toCommonType(runcases[chosen].typ)))
+ typ := toCommonType(tt.elem)
+ fl := flag(typ.Kind()) << flagKindShift
+ if typ.size > ptrSize {
+ fl |= flagIndir
+ }
+ recv = Value{typ, unsafe.Pointer(word), fl}
+ }
+ return chosen, recv, recvOK
+}
+
/*
* constructors
*/
diff --git a/src/pkg/runtime/chan.c b/src/pkg/runtime/chan.c
index 93408c2..f2e49c6 100644
--- a/src/pkg/runtime/chan.c
+++ b/src/pkg/runtime/chan.c
@@ -999,11 +999,17 @@
runtime·ready(gp);
retc:
- // return to pc corresponding to chosen case
+ // return pc corresponding to chosen case.
+ // Set boolean passed during select creation
+ // (at offset selp + cas->so) to true.
+ // If cas->so == 0, this is a reflect-driven select and we
+ // don't need to update the boolean.
pc = cas->pc;
- as = (byte*)selp + cas->so;
+ if(cas->so > 0) {
+ as = (byte*)selp + cas->so;
+ *as = true;
+ }
runtime·free(sel);
- *as = true;
return pc;
sclose:
@@ -1013,6 +1019,87 @@
return nil; // not reached
}
+// This struct must match ../reflect/value.go:/runtimeSelect.
+typedef struct runtimeSelect runtimeSelect;
+struct runtimeSelect
+{
+ uintptr dir;
+ ChanType *typ;
+ Hchan *ch;
+ uintptr val;
+};
+
+// This enum must match ../reflect/value.go:/SelectDir.
+enum SelectDir {
+ SelectSend = 1,
+ SelectRecv,
+ SelectDefault,
+};
+
+// func rselect(cases []runtimeSelect) (chosen int, word uintptr, recvOK bool)
+void
+reflect·rselect(Slice cases, int32 chosen, uintptr word, bool recvOK)
+{
+ int32 i;
+ Select *sel;
+ runtimeSelect* rcase, *rc;
+ void *elem;
+ void *recvptr;
+ uintptr maxsize;
+
+ chosen = -1;
+ word = 0;
+ recvOK = false;
+
+ maxsize = 0;
+ rcase = (runtimeSelect*)cases.array;
+ for(i=0; i<cases.len; i++) {
+ rc = &rcase[i];
+ if(rc->dir == SelectRecv && rc->ch != nil && maxsize < rc->typ->elem->size)
+ maxsize = rc->typ->elem->size;
+ }
+
+ recvptr = nil;
+ if(maxsize > sizeof(void*))
+ recvptr = runtime·mal(maxsize);
+
+ newselect(cases.len, &sel);
+ for(i=0; i<cases.len; i++) {
+ rc = &rcase[i];
+ switch(rc->dir) {
+ case SelectDefault:
+ selectdefault(sel, (void*)i, 0);
+ break;
+ case SelectSend:
+ if(rc->ch == nil)
+ break;
+ if(rc->typ->elem->size > sizeof(void*))
+ elem = (void*)rc->val;
+ else
+ elem = (void*)&rc->val;
+ selectsend(sel, rc->ch, (void*)i, elem, 0);
+ break;
+ case SelectRecv:
+ if(rc->ch == nil)
+ break;
+ if(rc->typ->elem->size > sizeof(void*))
+ elem = recvptr;
+ else
+ elem = &word;
+ selectrecv(sel, rc->ch, (void*)i, elem, &recvOK, 0);
+ break;
+ }
+ }
+
+ chosen = (int32)(uintptr)selectgo(&sel);
+ if(rcase[chosen].dir == SelectRecv && rcase[chosen].typ->elem->size > sizeof(void*))
+ word = (uintptr)recvptr;
+
+ FLUSH(&chosen);
+ FLUSH(&word);
+ FLUSH(&recvOK);
+}
+
// closechan(sel *byte);
void
runtime·closechan(Hchan *c)
