avoid data race by calling forceCompState only on commandRuntime.Run

Instead of using the component state to show the error, log it using the component stderr logger

changelog/fragments/1696516399-Avoid-possible-data-race-when-diring-a-component-start-the-Elastic-Agent-fails-to-write-to-the-component's-stdin.yaml

@@ -0,0 +1,32 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: bug
+
+# Change summary; a 80ish characters long description of the change.
+summary: Avoid possible data race when diring a component start the Elastic Agent fails to write to the component's stdin
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+# NOTE: This field will be rendered only for breaking-change and known-issue kinds at the moment.
+#description:
+
+# Affected component; a word indicating the component this changeset affects.
+component: component/runtime
+
+# PR URL; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: https://github.com/owner/repo/1234
+
+# Issue URL; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+#issue: https://github.com/owner/repo/1234

pkg/component/runtime/command.go

@@ -422,7 +422,7 @@ func (c *commandRuntime) startWatcher(info *process.Info, comm Communicator) {
 	go func() {
 		err := comm.WriteConnInfo(info.Stdin)
 		if err != nil {
-			c.forceCompState(client.UnitStateFailed, fmt.Sprintf("Failed: failed to provide connection information to spawned pid '%d': %s", info.PID, err))
+			_, _ = c.logErr.Write([]byte(fmt.Sprintf("Failed: failed to provide connection information to spawned pid '%d': %s", info.PID, err)))
 			// kill instantly
 			_ = info.Kill()
 		} else {

pkg/component/runtime/manager_test.go

@@ -2481,18 +2481,21 @@ func TestManager_FakeInput_RestartsOnMissedCheckins(t *testing.T) {
 				return
 			case state := <-sub.Ch():
 				t.Logf("component state changed: %+v", state)
-				if state.State == client.UnitStateStarting || state.State == client.UnitStateHealthy {
+
+				switch state.State {
+				case client.UnitStateStarting:
+				case client.UnitStateHealthy:
 					// starting and healthy are allowed
-				} else if state.State == client.UnitStateDegraded {
+				case client.UnitStateDegraded:
 					// should go to degraded first
 					wasDegraded = true
-				} else if state.State == client.UnitStateFailed {
+				case client.UnitStateFailed:
 					if wasDegraded {
 						subErrCh <- nil
 					} else {
 						subErrCh <- errors.New("should have been degraded before failed")
 					}
-				} else {
+				default:
 					subErrCh <- fmt.Errorf("unknown component state: %v", state.State)
 				}
 			}

pkg/component/runtime/state.go

@@ -462,7 +462,9 @@ func (s *ComponentState) cleanupStopped() bool {
 	return cleaned
 }
 
-// forceState force updates the state for the entire component, forcing that state on all units.
+// forceState force updates the state for the entire component, forcing that
+// state on all units. It returns true if either the component state or any of
+// the units state changed, false otherwise.
 func (s *ComponentState) forceState(state client.UnitState, msg string) bool {
 	changed := false
 	if s.State != state || s.Message != msg {