runtime: add cap and len support for chans

Author: cornelk

compiler/compiler.go

@@ -1201,9 +1201,7 @@ func (b *builder) createBuiltin(args []ssa.Value, callName string, pos token.Pos
 		var llvmCap llvm.Value
 		switch args[0].Type().(type) {
 		case *types.Chan:
-			// Channel. Buffered channels haven't been implemented yet so always
-			// return 0.
-			llvmCap = llvm.ConstInt(b.intType, 0, false)
+			llvmCap = b.createRuntimeCall("chanCap", []llvm.Value{value}, "cap")
 		case *types.Slice:
 			llvmCap = b.CreateExtractValue(value, 2, "cap")
 		default:
@@ -1259,9 +1257,7 @@ func (b *builder) createBuiltin(args []ssa.Value, callName string, pos token.Pos
 			// string or slice
 			llvmLen = b.CreateExtractValue(value, 1, "len")
 		case *types.Chan:
-			// Channel. Buffered channels haven't been implemented yet so always
-			// return 0.
-			llvmLen = llvm.ConstInt(b.intType, 0, false)
+			llvmLen = b.createRuntimeCall("chanLen", []llvm.Value{value}, "len")
 		case *types.Map:
 			llvmLen = b.createRuntimeCall("hashmapLen", []llvm.Value{value}, "len")
 		default:

src/runtime/chan.go

@@ -136,6 +136,38 @@ func chanMake(elementSize uintptr, bufSize uintptr) *channel {
 	}
 }
 
+// Return the number of entries in this chan, called from the len builtin.
+// A nil chan is defined as having length 0.
+//go:inline
+func chanLen(c *channel) int {
+	if c == nil {
+		return 0
+	}
+	return int(c.bufUsed)
+}
+
+// wrapper for use in reflect
+func chanLenUnsafePointer(p unsafe.Pointer) int {
+	c := (*channel)(p)
+	return chanLen(c)
+}
+
+// Return the capacity of this chan, called from the cap builtin.
+// A nil chan is defined as having capacity 0.
+//go:inline
+func chanCap(c *channel) int {
+	if c == nil {
+		return 0
+	}
+	return int(c.bufSize)
+}
+
+// wrapper for use in reflect
+func chanCapUnsafePointer(p unsafe.Pointer) int {
+	c := (*channel)(p)
+	return chanCap(c)
+}
+
 // resumeRX resumes the next receiver and returns the destination pointer.
 // If the ok value is true, then the caller is expected to store a value into this pointer.
 func (ch *channel) resumeRX(ok bool) unsafe.Pointer {

testdata/channel.go

@@ -9,7 +9,11 @@ import (
 var wg sync.WaitGroup
 
 func main() {
-	ch := make(chan int)
+	ch := make(chan int, 2)
+	ch <- 1
+	println("len, cap of channel:", len(ch), cap(ch), ch == nil)
+
+	ch = make(chan int)
 	println("len, cap of channel:", len(ch), cap(ch), ch == nil)
 
 	wg.Add(1)

testdata/channel.txt

@@ -1,3 +1,4 @@
+len, cap of channel: 1 2 false
 len, cap of channel: 0 0 false
 recv from open channel: 1 true
 received num: 2