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Refactor process state management (#70) (#73)

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* add isValidStateTransition helper function
* Replace Process.setState() with Process.swapState()
* Refactor locking logic in Process
This commit is contained in:
Benson Wong
2025-03-15 17:14:03 -07:00
committed by GitHub
parent a3f82c140b
commit d625ab8d92
2 changed files with 123 additions and 132 deletions
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182
proxy/process.go
View File

@@ -34,7 +34,9 @@ type Process struct {
config ModelConfig
cmd *exec.Cmd
logMonitor *LogMonitor
healthCheckTimeout int
healthCheckLoopInterval time.Duration
lastRequestHandled time.Time
@@ -59,46 +61,52 @@ func NewProcess(ID string, healthCheckTimeout int, config ModelConfig, logMonito
cmd: nil,
logMonitor: logMonitor,
healthCheckTimeout: healthCheckTimeout,
healthCheckLoopInterval: 5 * time.Second, /* default, can not be set by user - used for testing */
state: StateStopped,
shutdownCtx: ctx,
shutdownCancel: cancel,
}
}
func (p *Process) setState(newState ProcessState) error {
// enforce valid state transitions
invalidTransition := false
if p.state == StateStopped {
// stopped -> starting
if newState != StateStarting {
invalidTransition = true
}
} else if p.state == StateStarting {
// starting -> ready | failed | stopping
if newState != StateReady && newState != StateFailed && newState != StateStopping {
invalidTransition = true
}
} else if p.state == StateReady {
// ready -> stopping
if newState != StateStopping {
invalidTransition = true
}
} else if p.state == StateStopping {
// stopping -> stopped | shutdown
if newState != StateStopped && newState != StateShutdown {
invalidTransition = true
}
} else if p.state == StateFailed || p.state == StateShutdown {
invalidTransition = true
// custom error types for swapping state
var (
ErrExpectedStateMismatch = errors.New("expected state mismatch")
ErrInvalidStateTransition = errors.New("invalid state transition")
)
// swapState performs a compare and swap of the state atomically. It returns the current state
// and an error if the swap failed.
func (p *Process) swapState(expectedState, newState ProcessState) (ProcessState, error) {
p.stateMutex.Lock()
defer p.stateMutex.Unlock()
if p.state != expectedState {
return p.state, ErrExpectedStateMismatch
}
if invalidTransition {
//panic(fmt.Sprintf("Invalid state transition from %s to %s", p.state, newState))
return fmt.Errorf("invalid state transition from %s to %s", p.state, newState)
if !isValidTransition(p.state, newState) {
return p.state, ErrInvalidStateTransition
}
p.state = newState
return nil
return p.state, nil
}
// Helper function to encapsulate transition rules
func isValidTransition(from, to ProcessState) bool {
switch from {
case StateStopped:
return to == StateStarting
case StateStarting:
return to == StateReady || to == StateFailed || to == StateStopping
case StateReady:
return to == StateStopping
case StateStopping:
return to == StateStopped || to == StateShutdown
case StateFailed, StateShutdown:
return false // No transitions allowed from these states
}
return false
}
func (p *Process) CurrentState() ProcessState {
@@ -116,56 +124,33 @@ func (p *Process) start() error {
return fmt.Errorf("can not start(), upstream proxy missing")
}
// multiple start() calls will wait for the one that is actually starting to
// complete before proceeding.
// ===========
curState := p.CurrentState()
if curState == StateReady {
return nil
}
if curState == StateStarting {
p.waitStarting.Wait()
if state := p.CurrentState(); state != StateReady {
return fmt.Errorf("start() failed current state: %v", state)
}
return nil
}
// ===========
// There is the possibility of a hard to replicate race condition where
// curState *WAS* StateStopped but by the time we get to the p.stateMutex.Lock()
// below, it's value has changed!
p.stateMutex.Lock()
defer p.stateMutex.Unlock()
// with the exclusive lock, check if p.state is StateStopped, which is the only valid state
// to transition from to StateReady
if p.state != StateStopped {
if p.state == StateReady {
return nil
} else {
return fmt.Errorf("start() can not proceed expected StateReady but process is in %v", p.state)
}
}
if err := p.setState(StateStarting); err != nil {
return err
}
p.waitStarting.Add(1)
defer p.waitStarting.Done()
args, err := p.config.SanitizedCommand()
if err != nil {
return fmt.Errorf("unable to get sanitized command: %v", err)
}
if curState, err := p.swapState(StateStopped, StateStarting); err != nil {
if err == ErrExpectedStateMismatch {
// already starting, just wait for it to complete and expect
// it to be be in the Ready start after. If not, return an error
if curState == StateStarting {
p.waitStarting.Wait()
if state := p.CurrentState(); state == StateReady {
return nil
} else {
return fmt.Errorf("process was already starting but wound up in state %v", state)
}
} else {
return fmt.Errorf("processes was in state %v when start() was called", curState)
}
} else {
return fmt.Errorf("failed to set Process state to starting: current state: %v, error: %v", curState, err)
}
}
p.waitStarting.Add(1)
defer p.waitStarting.Done()
p.cmd = exec.Command(args[0], args[1:]...)
p.cmd.Stdout = p.logMonitor
p.cmd.Stderr = p.logMonitor
@@ -173,8 +158,14 @@ func (p *Process) start() error {
err = p.cmd.Start()
// Set process state to failed
if err != nil {
p.setState(StateFailed)
if curState, swapErr := p.swapState(StateStarting, StateFailed); err != nil {
return fmt.Errorf(
"failed to start command and state swap failed. command error: %v, current state: %v, state swap error: %v",
err, curState, swapErr,
)
}
return fmt.Errorf("start() failed: %v", err)
}
@@ -209,13 +200,16 @@ func (p *Process) start() error {
)
defer cancelHealthCheck()
// Health check loop
loop:
// Ready Check loop
for {
select {
case <-checkDeadline.Done():
p.setState(StateFailed)
return fmt.Errorf("health check failed after %vs", maxDuration.Seconds())
if curState, err := p.swapState(StateStarting, StateFailed); err != nil {
return fmt.Errorf("health check timed out after %vs AND state swap failed: %v, current state: %v", maxDuration.Seconds(), err, curState)
} else {
return fmt.Errorf("health check timed out after %vs", maxDuration.Seconds())
}
case <-p.shutdownCtx.Done():
return errors.New("health check interrupted due to shutdown")
default:
@@ -233,7 +227,7 @@ func (p *Process) start() error {
}
}
<-time.After(5 * time.Second)
<-time.After(p.healthCheckLoopInterval)
}
}
@@ -244,7 +238,7 @@ func (p *Process) start() error {
maxDuration := time.Duration(p.config.UnloadAfter) * time.Second
for range time.Tick(time.Second) {
if p.state != StateReady {
if p.CurrentState() != StateReady {
return
}
@@ -260,26 +254,28 @@ func (p *Process) start() error {
}()
}
return p.setState(StateReady)
if curState, err := p.swapState(StateStarting, StateReady); err != nil {
return fmt.Errorf("failed to set Process state to ready: current state: %v, error: %v", curState, err)
} else {
return nil
}
}
func (p *Process) Stop() {
// wait for any inflight requests before proceeding
p.inFlightRequests.Wait()
p.stateMutex.Lock()
defer p.stateMutex.Unlock()
// calling Stop() when state is invalid is a no-op
if err := p.setState(StateStopping); err != nil {
fmt.Fprintf(p.logMonitor, "!!! Info - Stop() err: %v\n", err)
if curState, err := p.swapState(StateReady, StateStopping); err != nil {
fmt.Fprintf(p.logMonitor, "!!! Info - Stop() Ready -> StateStopping err: %v, current state: %v\n", err, curState)
return
}
// stop the process with a graceful exit timeout
p.stopCommand(5 * time.Second)
if err := p.setState(StateStopped); err != nil {
panic(fmt.Sprintf("Stop() failed to set state to stopped: %v", err))
if curState, err := p.swapState(StateStopping, StateStopped); err != nil {
fmt.Fprintf(p.logMonitor, "!!! Info - Stop() StateStopping -> StateStopped err: %v, current state: %v\n", err, curState)
}
}
@@ -287,19 +283,9 @@ func (p *Process) Stop() {
// of time for any inflight requests to complete before shutting down. If the Process
// is in the state of starting, it will cancel it and shut it down
func (p *Process) Shutdown() {
// cancel anything that can be interrupted by a shutdown (ie: healthcheck)
p.shutdownCancel()
p.stateMutex.Lock()
defer p.stateMutex.Unlock()
p.setState(StateStopping)
// 5 seconds to stop the process
p.stopCommand(5 * time.Second)
if err := p.setState(StateShutdown); err != nil {
fmt.Printf("!!! Shutdown() failed to set state to shutdown: %v", err)
}
p.setState(StateShutdown)
p.state = StateShutdown
}
// stopCommand will send a SIGTERM to the process and wait for it to exit.

47
proxy/process_test.go
View File

@@ -225,30 +225,32 @@ func TestProcess_HTTPRequestsHaveTimeToFinish(t *testing.T) {
}
}
func TestSetState(t *testing.T) {
func TestProcess_SwapState(t *testing.T) {
tests := []struct {
name string
currentState ProcessState
expectedState ProcessState
newState ProcessState
expectedError error
expectedResult ProcessState
}{
{"Stopped to Starting", StateStopped, StateStarting, nil, StateStarting},
{"Starting to Ready", StateStarting, StateReady, nil, StateReady},
{"Starting to Failed", StateStarting, StateFailed, nil, StateFailed},
{"Starting to Stopping", StateStarting, StateStopping, nil, StateStopping},
{"Ready to Stopping", StateReady, StateStopping, nil, StateStopping},
{"Stopping to Stopped", StateStopping, StateStopped, nil, StateStopped},
{"Stopping to Shutdown", StateStopping, StateShutdown, nil, StateShutdown},
{"Stopped to Ready", StateStopped, StateReady, fmt.Errorf("invalid state transition from stopped to ready"), StateStopped},
{"Starting to Stopped", StateStarting, StateStopped, fmt.Errorf("invalid state transition from starting to stopped"), StateStarting},
{"Ready to Starting", StateReady, StateStarting, fmt.Errorf("invalid state transition from ready to starting"), StateReady},
{"Ready to Failed", StateReady, StateFailed, fmt.Errorf("invalid state transition from ready to failed"), StateReady},
{"Stopping to Ready", StateStopping, StateReady, fmt.Errorf("invalid state transition from stopping to ready"), StateStopping},
{"Failed to Stopped", StateFailed, StateStopped, fmt.Errorf("invalid state transition from failed to stopped"), StateFailed},
{"Failed to Starting", StateFailed, StateStarting, fmt.Errorf("invalid state transition from failed to starting"), StateFailed},
{"Shutdown to Stopped", StateShutdown, StateStopped, fmt.Errorf("invalid state transition from shutdown to stopped"), StateShutdown},
{"Shutdown to Starting", StateShutdown, StateStarting, fmt.Errorf("invalid state transition from shutdown to starting"), StateShutdown},
{"Stopped to Starting", StateStopped, StateStopped, StateStarting, nil, StateStarting},
{"Starting to Ready", StateStarting, StateStarting, StateReady, nil, StateReady},
{"Starting to Failed", StateStarting, StateStarting, StateFailed, nil, StateFailed},
{"Starting to Stopping", StateStarting, StateStarting, StateStopping, nil, StateStopping},
{"Ready to Stopping", StateReady, StateReady, StateStopping, nil, StateStopping},
{"Stopping to Stopped", StateStopping, StateStopping, StateStopped, nil, StateStopped},
{"Stopping to Shutdown", StateStopping, StateStopping, StateShutdown, nil, StateShutdown},
{"Stopped to Ready", StateStopped, StateStopped, StateReady, ErrInvalidStateTransition, StateStopped},
{"Starting to Stopped", StateStarting, StateStarting, StateStopped, ErrInvalidStateTransition, StateStarting},
{"Ready to Starting", StateReady, StateReady, StateStarting, ErrInvalidStateTransition, StateReady},
{"Ready to Failed", StateReady, StateReady, StateFailed, ErrInvalidStateTransition, StateReady},
{"Stopping to Ready", StateStopping, StateStopping, StateReady, ErrInvalidStateTransition, StateStopping},
{"Failed to Stopped", StateFailed, StateFailed, StateStopped, ErrInvalidStateTransition, StateFailed},
{"Failed to Starting", StateFailed, StateFailed, StateStarting, ErrInvalidStateTransition, StateFailed},
{"Shutdown to Stopped", StateShutdown, StateShutdown, StateStopped, ErrInvalidStateTransition, StateShutdown},
{"Shutdown to Starting", StateShutdown, StateShutdown, StateStarting, ErrInvalidStateTransition, StateShutdown},
{"Expected state mismatch", StateStopped, StateStarting, StateStarting, ErrExpectedStateMismatch, StateStopped},
}
for _, test := range tests {
@@ -257,7 +259,7 @@ func TestSetState(t *testing.T) {
state: test.currentState,
}
err := p.setState(test.newState)
resultState, err := p.swapState(test.expectedState, test.newState)
if err != nil && test.expectedError == nil {
t.Errorf("Unexpected error: %v", err)
} else if err == nil && test.expectedError != nil {
@@ -268,8 +270,8 @@ func TestSetState(t *testing.T) {
}
}
if p.state != test.expectedResult {
t.Errorf("Expected state: %v, got: %v", test.expectedResult, p.state)
if resultState != test.expectedResult {
t.Errorf("Expected state: %v, got: %v", test.expectedResult, resultState)
}
})
}
@@ -290,11 +292,14 @@ func TestProcess_ShutdownInterruptsHealthCheck(t *testing.T) {
healthCheckTTLSeconds := 30
process := NewProcess("test-process", healthCheckTTLSeconds, config, logMonitor)
// make it a lot faster
process.healthCheckLoopInterval = time.Second
// start a goroutine to simulate a shutdown
var wg sync.WaitGroup
go func() {
defer wg.Done()
<-time.After(time.Second * 2)
<-time.After(time.Millisecond * 500)
process.Shutdown()
}()
wg.Add(1)