cgen: implement channel `select` block code generation (#6424)

vlib/sync/channel_select_3_test.v

@@ -0,0 +1,97 @@
+import time
+import sync
+
+struct St {
+	a int
+}
+
+fn f1(ch1 chan int, ch2 chan St, ch3 chan int, sem sync.Semaphore) {
+	mut a := 5
+	st := St{}
+	select {
+		a = <-ch3 {
+			a = 0
+		}
+		b := <-ch2 {
+			a = b.a
+		}
+		ch2 <- st {
+			a = 2
+		}
+		> 300 * time.millisecond {
+			a = 3
+		}
+	}
+	assert a == 3
+	sem.post()
+}
+
+fn f2(ch1 chan St, ch2 chan int, sem sync.Semaphore) {
+	mut r := 23
+	for i in 0 .. 2 {
+		select {
+			b := <- ch1 {
+				r = b.a
+			}
+			ch2 <- r {
+				r = 17
+			}
+		}
+		if i == 0 {
+			assert r == 17
+		} else {
+			assert r == 13
+		}
+	}
+	sem.post()
+} 
+
+fn test_select_blocks() {
+	ch1 := chan int{cap: 1}
+	ch2 := chan St{}
+	ch3 := chan int{}
+	sem := sync.new_semaphore()
+	mut r := false
+	t := select {
+		b := <- ch1 {
+			println(b)
+		}
+		else {
+			// no channel ready
+			r = true
+		}
+	}
+	assert r == true
+	assert t == true
+	go f2(ch2, ch3, sem)
+	n := <-ch3
+	assert n == 23
+	ch2 <- St{a: 13}
+	sem.wait()
+	stopwatch := time.new_stopwatch({})
+	go f1(ch1, ch2, ch3, sem)
+	sem.wait()
+	elapsed_ms := f64(stopwatch.elapsed()) / time.millisecond
+	assert elapsed_ms >= 295.0
+
+	ch1.close()
+	ch2.close()
+	mut h := 7
+	u := select {
+		b := <- ch2 {
+			h = 0
+		}
+		ch1 <- h {
+			h = 1
+		}
+		else {
+			h = 2
+		}
+	}
+	// no branch should have run
+	assert h == 7
+	// since all channels are closed `select` should return `false`
+	assert u == false
+}
+
+			

vlib/v/ast/ast.v

@@ -536,9 +536,9 @@ pub struct SelectExpr {
 pub:
 	branches      []SelectBranch
 	pos           token.Position
+	has_exception bool
 pub mut:
 	is_expr       bool // returns a value
-	return_type   table.Type
 	expected_type table.Type // for debugging only
 }
 

vlib/v/checker/checker.v

@@ -2656,8 +2656,7 @@ pub fn (mut c Checker) expr(node ast.Expr) table.Type {
 			return table.void_type
 		}
 		ast.SelectExpr {
-			// TODO: to be implemented
-			return table.void_type
+			return c.select_expr(mut node)
 		}
 		ast.SelectorExpr {
 			return c.selector_expr(mut node)
@@ -3060,6 +3059,16 @@ fn (mut c Checker) match_exprs(mut node ast.MatchExpr, type_sym table.TypeSymbol
 	c.error(err_details, node.pos)
 }
 
+pub fn (mut c Checker) select_expr(mut node ast.SelectExpr) table.Type {
+	node.is_expr = c.expected_type != table.void_type
+	node.expected_type = c.expected_type
+	for branch in node.branches {
+		c.stmt(branch.stmt)
+		c.stmts(branch.stmts)
+	}
+	return table.bool_type
+}
+
 pub fn (mut c Checker) lock_expr(mut node ast.LockExpr) table.Type {
 	for id in node.lockeds {
 		c.ident(mut id)

vlib/v/gen/cgen.v

@@ -2129,7 +2129,7 @@ fn (mut g Gen) expr(node ast.Expr) {
 			// Only used in IndexExpr
 		}
 		ast.SelectExpr {
-			// TODO: to be implemented
+			g.select_expr(node)
 		}
 		ast.SizeOf {
 			if node.is_type {
@@ -2739,6 +2739,142 @@ fn (mut g Gen) match_expr(node ast.MatchExpr) {
 	}
 }
 
+fn (mut g Gen) select_expr(node ast.SelectExpr) {
+	is_expr := node.is_expr || g.inside_ternary > 0
+	cur_line := if is_expr {
+		g.empty_line = true
+		g.go_before_stmt(0)
+	} else {
+		''
+	}
+	n_channels := if node.has_exception { node.branches.len - 1 } else { node.branches.len }
+	mut channels := []ast.Expr{cap: n_channels}
+	mut objs := []ast.Expr{cap: n_channels}
+	mut tmp_objs := []string{cap: n_channels}
+	mut elem_types := []string{cap: n_channels}
+	mut is_push := []bool{cap: n_channels}
+	mut has_else := false
+	mut has_timeout := false
+	mut timeout_expr := ast.Expr{}
+	mut exception_branch := -1
+	for j, branch in node.branches {
+		if branch.is_else {
+			has_else = true
+			exception_branch = j
+		} else if branch.is_timeout {
+			has_timeout = true
+			exception_branch = j
+			timeout_expr = (branch.stmt as ast.ExprStmt).expr
+		} else {
+			match branch.stmt as stmt {
+				ast.ExprStmt {
+					expr := stmt.expr as ast.InfixExpr
+					channels << expr.left
+					objs << expr.right
+					tmp_objs << ''
+					elem_types << ''
+					is_push << true
+				}
+				ast.AssignStmt {
+					rec_expr := stmt.right[0] as ast.PrefixExpr
+					channels << rec_expr.right
+					is_push << false
+					// create tmp unless the object with *exactly* the type we need exists already
+					if stmt.op == .decl_assign || stmt.right_types[0] != stmt.left_types[0] {
+						tmp_obj := g.new_tmp_var()
+						tmp_objs << tmp_obj
+						el_stype := g.typ(stmt.right_types[0])
+						elem_types << if stmt.op == .decl_assign {
+							el_stype + ' '
+						} else {
+							''
+						}
+						g.writeln('$el_stype $tmp_obj;')
+					} else {
+						tmp_objs << ''
+						elem_types << ''
+					}
+					objs << stmt.left[0]
+				}
+				else {}
+			}
+		}
+	}
+	chan_array := g.new_tmp_var()
+	g.write('array_sync__Channel_ptr $chan_array = new_array_from_c_array($n_channels, $n_channels, sizeof(sync__Channel*), _MOV((sync__Channel*[$n_channels]){')
+	for i in 0 .. n_channels {
+		if i > 0 {
+			g.write(', ')
+		}
+		g.write('(sync__Channel*)(')
+		g.expr(channels[i])
+		g.write(')')
+	}
+	g.writeln('}));')
+	directions_array := g.new_tmp_var()
+	g.write('array_sync__Direction $directions_array = new_array_from_c_array($n_channels, $n_channels, sizeof(sync__Direction), _MOV((sync__Direction[$n_channels]){')
+	for i in 0 .. n_channels {
+		if i > 0 {
+			g.write(', ')
+		}
+		if is_push[i] {
+			g.write('sync__Direction_push')
+		} else {
+			g.write('sync__Direction_pop')
+		}
+	}
+	g.writeln('}));')
+	objs_array := g.new_tmp_var()
+	g.write('array_voidptr $objs_array = new_array_from_c_array($n_channels, $n_channels, sizeof(voidptr), _MOV((voidptr[$n_channels]){')
+	for i in 0 .. n_channels {
+		g.write(if i > 0 {
+			', &'
+		} else {
+			'&'
+		})
+		if tmp_objs[i] == '' {
+			g.expr(objs[i])
+		} else {
+			g.write(tmp_objs[i])
+		}
+	}
+	g.writeln('}));')
+	select_result := g.new_tmp_var()
+	g.write('int $select_result = sync__channel_select(&/*arr*/$chan_array, $directions_array, &/*arr*/$objs_array, ')
+	if has_timeout {
+		g.expr(timeout_expr)
+	} else if has_else {
+		g.write('0')
+	} else {
+		g.write('-1')
+	}
+	g.writeln(');')
+	mut i := 0
+	for j in 0 .. node.branches.len {
+		if j > 0 {
+			g.write('} else ')
+		}
+		g.write('if ($select_result == ')
+		if j == exception_branch {
+			g.writeln('-1) {')
+		} else {
+			g.writeln('$i) {')
+			if tmp_objs[i] != '' {
+				g.write('\t${elem_types[i]}')
+				g.expr(objs[i])
+				g.writeln(' = ${tmp_objs[i]};')
+			}
+			i++
+		}
+		g.stmts(node.branches[j].stmts)
+	}
+	g.writeln('}')
+	if is_expr {
+		g.write(cur_line)
+		g.write('($select_result != -2)')
+	}
+}
+
 fn (mut g Gen) ident(node ast.Ident) {
 	if node.name == 'lld' {
 		return

vlib/v/parser/if_match.v

@@ -442,5 +442,6 @@ fn (mut p Parser) select_expr() ast.SelectExpr {
 	return ast.SelectExpr{
 		branches: branches
 		pos: pos
+		has_exception: has_else || has_timeout
 	}
 }