Check if watchdogs are closed before operating on them

src/watchdog.toit

@@ -123,6 +123,7 @@ class Watchdog extends ServiceResourceProxy:
     reacted upon.
   */
   start --s/int -> none:
+    if is-closed: throw "ALREADY_CLOSED"
     is-stopped_ = false
     client := (client_ as WatchdogServiceClient)
     client.start_ handle_ s
@@ -133,6 +134,7 @@ class Watchdog extends ServiceResourceProxy:
   Does nothing if the watchdog is not started.
   */
   feed -> none:
+    if is-closed: throw "ALREADY_CLOSED"
     client := (client_ as WatchdogServiceClient)
     client.feed_ handle_
 
@@ -142,6 +144,7 @@ class Watchdog extends ServiceResourceProxy:
   Does nothing if the watchdog is not started.
   */
   stop -> none:
+    if is-closed: throw "ALREADY_CLOSED"
     is-stopped_ = true
     client := (client_ as WatchdogServiceClient)
     client.stop_ handle_
@@ -152,4 +155,8 @@ class Watchdog extends ServiceResourceProxy:
   close -> none:
     super
     if not is-stopped_:
-      throw "WATCHDOG_NOT_STOPPED"
+      // Produce a stack trace to draw attention to the
+      // fact that a closed, non-stopped watchdog will
+      // eventually lead to problems, because it cannot
+      // be fed anymore.
+      catch --trace: throw "WATCHDOG_NOT_STOPPED"

tests/throw-close-test.toit

@@ -4,12 +4,40 @@
 
 import expect show *
 import watchdog show WatchdogServiceClient
+import system.services show ServiceProvider ServiceHandler
+import system.api.trace show TraceService
 
 import .util
 
 main:
+  service := TraceServiceProvider
+  service.install
   run-test: | client/WatchdogServiceClient ms/int system-dog/FakeSystemWatchdog |
     dog := client.create "toit.io/test/throw-close"
     dog.start --s=1
-    expect-throw "WATCHDOG_NOT_STOPPED":
-      dog.close
+    expect-equals 0 service.traces.size
+    dog.close
+    expect-equals 1 service.traces.size
+  service.uninstall
+
+class TraceServiceProvider extends ServiceProvider
+    implements TraceService ServiceHandler:
+  traces_/List := []
+
+  constructor:
+    super "system/trace/test" --major=1 --minor=2
+    provides TraceService.SELECTOR --handler=this
+
+  handle index/int arguments/any --gid/int --client/int -> any:
+    if index == TraceService.HANDLE-TRACE-INDEX:
+      return handle-trace arguments
+    unreachable
+
+  traces -> List:
+    result := traces_
+    traces_ = []
+    return result
+
+  handle-trace message/ByteArray -> ByteArray?:
+    traces_.add message
+    return null