context: small refactor to always use Context type instead of multiple types (#9705)

cmd/tools/vtest-self.v

@@ -58,6 +58,7 @@ const (
 		'vlib/context/value_test.v' /* the following tests need C casts in `sync` and/or thirdparty/stdatomic */,
 		'vlib/context/empty_test.v',
 		'vlib/context/cancel_test.v',
+		'vlib/context/deadline_test.v',
 		'vlib/sync/array_rlock_test.v',
 		'vlib/sync/atomic2/atomic_test.v',
 		'vlib/sync/channel_2_test.v',

vlib/context/README.md

@@ -10,10 +10,9 @@ with_deadline, with_timeout, or with_value. When a Context is canceled, all Cont
 derived from it are also canceled.
 
 The with_cancel, with_deadline, and with_timeout functions take a Context (the parent)
-and return a derived Context (the child) and a CancelFunc. Calling the CancelFunc
+and return a derived Context (the child). Calling the cancel function
 cancels the child and its children, removes the parent's reference to the child,
-and stops any associated timers. Failing to call the CancelFunc leaks the child
-and its children until the parent is canceled or the timer fires.
+and stops any associated timers.
 
 Programs that use Contexts should follow these rules to keep interfaces consistent
 across different modules.
@@ -40,29 +39,32 @@ fn example_with_cancel() {
 	// The callers of gen need to cancel the context once
 	// they are done consuming generated integers not to leak
 	// the internal routine started by gen.
-	gen := fn (mut ctx context.CancelerContext) chan int {
+	gen := fn (ctx context.Context) chan int {
 		dst := chan int{}
-		go fn (mut ctx context.CancelerContext, dst chan int) {
+		go fn (ctx context.Context, dst chan int) {
+			mut v := 0
 			ch := ctx.done()
-			loop: for i in 0 .. 5 {
+			for {
 				select {
 					_ := <-ch {
 						// returning not to leak the routine
-						break loop
+						return
+					}
+					dst <- v {
+						v++
 					}
-					dst <- i {}
 				}
 			}
-		}(mut ctx, dst)
+		}(ctx, dst)
 		return dst
 	}
 
-	mut ctx := context.with_cancel(context.background())
+	ctx := context.with_cancel(context.background())
 	defer {
-		context.cancel(mut ctx)
+		context.cancel(ctx)
 	}
 
-	ch := gen(mut ctx)
+	ch := gen(ctx)
 	for i in 0 .. 5 {
 		v := <-ch
 		assert i == v
@@ -94,13 +96,13 @@ fn after(dur time.Duration) chan int {
 // function that it should abandon its work as soon as it gets to it.
 fn example_with_deadline() {
 	dur := time.now().add(short_duration)
-	mut ctx := context.with_deadline(context.background(), dur)
+	ctx := context.with_deadline(context.background(), dur)
 
 	defer {
 		// Even though ctx will be expired, it is good practice to call its
 		// cancellation function in any case. Failure to do so may keep the
 		// context and its parent alive longer than necessary.
-		context.cancel(mut ctx)
+		context.cancel(ctx)
 	}
 
 	after_ch := after(1 * time.second)
@@ -141,9 +143,9 @@ fn after(dur time.Duration) chan int {
 fn example_with_timeout() {
 	// Pass a context with a timeout to tell a blocking function that it
 	// should abandon its work after the timeout elapses.
-	mut ctx := context.with_timeout(context.background(), short_duration)
+	ctx := context.with_timeout(context.background(), short_duration)
 	defer {
-		context.cancel(mut ctx)
+		context.cancel(ctx)
 	}
 
 	after_ch := after(1 * time.second)
@@ -169,7 +171,7 @@ type ValueContextKey = string
 // This example demonstrates how a value can be passed to the context
 // and also how to retrieve it if it exists.
 fn example_with_value() {
-	f := fn (ctx context.ValueContext, key ValueContextKey) string {
+	f := fn (ctx context.Context, key ValueContextKey) string {
 		if value := ctx.value(key) {
 			if !isnil(value) {
 				return *(&string(value))

vlib/context/_context.v

@@ -61,7 +61,7 @@ pub interface Context {
 // initialization, and tests, and as the top-level Context for incoming
 // requests.
 pub fn background() Context {
-	return Context(context.background)
+	return context.background
 }
 
 // todo returns an empty Context. Code should use todo when
@@ -69,7 +69,7 @@ pub fn background() Context {
 // surrounding function has not yet been extended to accept a Context
 // parameter).
 pub fn todo() Context {
-	return Context(context.todo)
+	return context.todo
 }
 
 fn context_name(ctx Context) string {

vlib/context/cancel.v

@@ -8,10 +8,9 @@ pub interface Canceler {
 	id string
 	cancel(remove_from_parent bool, err string)
 	done() chan int
-	str() string
 }
 
-pub fn cancel(mut ctx CancelerContext) {
+pub fn cancel(ctx Context) {
 	match mut ctx {
 		CancelContext {
 			ctx.cancel(true, canceled)
@@ -19,65 +18,7 @@ pub fn cancel(mut ctx CancelerContext) {
 		TimerContext {
 			ctx.cancel(true, canceled)
 		}
-	}
-}
-
-// CancelerContext implements the Canceler intarface for both
-// struct types: CancelContext and TimerContext
-pub type CancelerContext = CancelContext | TimerContext
-
-pub fn (mut ctx CancelerContext) done() chan int {
-	match mut ctx {
-		CancelContext {
-			return ctx.done()
-		}
-		TimerContext {
-			return ctx.done()
-		}
-	}
-}
-
-pub fn (mut ctx CancelerContext) err() string {
-	match mut ctx {
-		CancelContext {
-			return ctx.err()
-		}
-		TimerContext {
-			return ctx.err()
-		}
-	}
-}
-
-pub fn (ctx CancelerContext) value(key string) ?voidptr {
-	match ctx {
-		CancelContext {
-			return ctx.value(key)
-		}
-		TimerContext {
-			return ctx.value(key)
-		}
-	}
-}
-
-pub fn (mut ctx CancelerContext) cancel(remove_from_parent bool, err string) {
-	match mut ctx {
-		CancelContext {
-			ctx.cancel(remove_from_parent, err)
-		}
-		TimerContext {
-			ctx.cancel(remove_from_parent, err)
-		}
-	}
-}
-
-pub fn (ctx CancelerContext) str() string {
-	match ctx {
-		CancelContext {
-			return ctx.str()
-		}
-		TimerContext {
-			return ctx.str()
-		}
+		else {}
 	}
 }
 
@@ -93,22 +34,16 @@ mut:
 	err      string
 }
 
-// A CancelFunc tells an operation to abandon its work.
-// A CancelFunc does not wait for the work to stop.
-// A CancelFunc may be called by multiple goroutines simultaneously.
-// After the first call, subsequent calls to a CancelFunc do nothing.
-// pub type CancelFunc = fn (c Canceler)
-
 // with_cancel returns a copy of parent with a new done channel. The returned
 // context's done channel is closed when the returned cancel function is called
 // or when the parent context's done channel is closed, whichever happens first.
 //
 // Canceling this context releases resources associated with it, so code should
 // call cancel as soon as the operations running in this Context complete.
-pub fn with_cancel(parent Context) &CancelerContext {
+pub fn with_cancel(parent Context) Context {
 	mut c := new_cancel_context(parent)
 	propagate_cancel(parent, mut c)
-	return c
+	return Context(c)
 }
 
 // new_cancel_context returns an initialized CancelContext.
@@ -164,6 +99,7 @@ fn (mut ctx CancelContext) cancel(remove_from_parent bool, err string) {
 	ctx.err = err
 
 	if !ctx.done.closed {
+		ctx.done <- 0
 		ctx.done.close()
 	}
 

vlib/context/cancel_test.v

@@ -9,29 +9,32 @@ fn test_with_cancel() {
 	// The callers of gen need to cancel the context once
 	// they are done consuming generated integers not to leak
 	// the internal routine started by gen.
-	gen := fn (mut ctx context.CancelerContext) chan int {
+	gen := fn (ctx context.Context) chan int {
 		dst := chan int{}
-		go fn (mut ctx context.CancelerContext, dst chan int) {
+		go fn (ctx context.Context, dst chan int) {
+			mut v := 0
 			ch := ctx.done()
-			loop: for i in 0 .. 5 {
+			for {
 				select {
 					_ := <-ch {
 						// returning not to leak the routine
-						break loop
+						return
+					}
+					dst <- v {
+						v++
 					}
-					dst <- i {}
 				}
 			}
-		}(mut ctx, dst)
+		}(ctx, dst)
 		return dst
 	}
 
-	mut ctx := context.with_cancel(context.background())
+	ctx := context.with_cancel(context.background())
 	defer {
-		context.cancel(mut ctx)
+		context.cancel(ctx)
 	}
 
-	ch := gen(mut ctx)
+	ch := gen(ctx)
 	for i in 0 .. 5 {
 		v := <-ch
 		assert i == v

vlib/context/deadline.v

@@ -22,7 +22,7 @@ mut:
 //
 // Canceling this context releases resources associated with it, so code should
 // call cancel as soon as the operations running in this Context complete.
-pub fn with_deadline(parent Context, d time.Time) &CancelerContext {
+pub fn with_deadline(parent Context, d time.Time) Context {
 	id := rand.uuid_v4()
 	if cur := parent.deadline() {
 		if cur < d {
@@ -40,25 +40,23 @@ pub fn with_deadline(parent Context, d time.Time) &CancelerContext {
 	dur := d - time.now()
 	if dur.nanoseconds() <= 0 {
 		ctx.cancel(true, deadline_exceeded) // deadline has already passed
-		return ctx
+		return Context(ctx)
 	}
 
 	if ctx.cancel_ctx.err() == '' {
 		go fn (mut ctx TimerContext, dur time.Duration) {
 			time.sleep(dur)
-			ctx_ch := ctx.done()
-			ctx_ch <- 0
 			ctx.cancel(true, deadline_exceeded)
 		}(mut ctx, dur)
 	}
-	return ctx
+	return Context(ctx)
 }
 
 // with_timeout returns with_deadline(parent, time.now().add(timeout)).
 //
 // Canceling this context releases resources associated with it, so code should
 // call cancel as soon as the operations running in this Context complete
-pub fn with_timeout(parent Context, timeout time.Duration) &CancelerContext {
+pub fn with_timeout(parent Context, timeout time.Duration) Context {
 	return with_deadline(parent, time.now().add(timeout))
 }
 

vlib/context/deadline_test.v

@@ -0,0 +1,63 @@
+import context
+import time
+
+const (
+	// a reasonable duration to block in an example
+	short_duration = 1 * time.millisecond
+)
+
+fn after(dur time.Duration) chan int {
+	dst := chan int{}
+	go fn (dur time.Duration, dst chan int) {
+		time.sleep(dur)
+		dst <- 0
+	}(dur, dst)
+	return dst
+}
+
+// This example passes a context with an arbitrary deadline to tell a blocking
+// function that it should abandon its work as soon as it gets to it.
+fn test_with_deadline() {
+	dur := time.now().add(short_duration)
+	ctx := context.with_deadline(context.background(), dur)
+
+	defer {
+		// Even though ctx will be expired, it is good practice to call its
+		// cancellation function in any case. Failure to do so may keep the
+		// context and its parent alive longer than necessary.
+		context.cancel(ctx)
+	}
+
+	after_ch := after(1 * time.second)
+	ctx_ch := ctx.done()
+	select {
+		_ := <-after_ch {
+			assert false
+		}
+		_ := <-ctx_ch {
+			assert true
+		}
+	}
+}
+
+// This example passes a context with a timeout to tell a blocking function that
+// it should abandon its work after the timeout elapses.
+fn test_with_timeout() {
+	// Pass a context with a timeout to tell a blocking function that it
+	// should abandon its work after the timeout elapses.
+	ctx := context.with_timeout(context.background(), short_duration)
+	defer {
+		context.cancel(ctx)
+	}
+
+	after_ch := after(1 * time.second)
+	ctx_ch := ctx.done()
+	select {
+		_ := <-after_ch {
+			assert false
+		}
+		_ := <-ctx_ch {
+			assert true
+		}
+	}
+}

vlib/context/value.v

@@ -21,10 +21,7 @@ mut:
 // string or any other built-in type to avoid collisions between
 // packages using context. Users of with_value should define their own
 // types for keys
-pub fn with_value(parent Context, key string, value voidptr) &ValueContext {
-	if isnil(key) {
-		panic('nil key')
-	}
+pub fn with_value(parent Context, key string, value voidptr) Context {
 	return &ValueContext{
 		context: parent
 		key: key

vlib/context/value_test.v

@@ -5,7 +5,7 @@ type ValueContextKey = string
 // This example demonstrates how a value can be passed to the context
 // and also how to retrieve it if it exists.
 fn test_with_value() {
-	f := fn (ctx context.ValueContext, key ValueContextKey) string {
+	f := fn (ctx context.Context, key ValueContextKey) string {
 		if value := ctx.value(key) {
 			if !isnil(value) {
 				return *(&string(value))