wings/server/power.go

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package server
import (
"context"
"github.com/pkg/errors"
"golang.org/x/sync/semaphore"
"os"
"time"
)
type PowerAction string
// The power actions that can be performed for a given server. This taps into the given server
// environment and performs them in a way that prevents a race condition from occurring. For
// example, sending two "start" actions back to back will not process the second action until
// the first action has been completed.
//
// This utilizes a workerpool with a limit of one worker so that all of the actions execute
// in a sync manner.
const (
PowerActionStart = "start"
PowerActionStop = "stop"
PowerActionRestart = "restart"
PowerActionTerminate = "kill"
)
// Checks if the power action being received is valid.
func (pa PowerAction) IsValid() bool {
return pa == PowerActionStart ||
pa == PowerActionStop ||
pa == PowerActionTerminate ||
pa == PowerActionRestart
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}
func (pa PowerAction) IsStart() bool {
return pa == PowerActionStart || pa == PowerActionRestart
}
// Helper function that can receive a power action and then process the actions that need
// to occur for it. This guards against someone calling Start() twice at the same time, or
// trying to restart while another restart process is currently running.
//
// However, the code design for the daemon does depend on the user correctly calling this
// function rather than making direct calls to the start/stop/restart functions on the
// environment struct.
func (s *Server) HandlePowerAction(action PowerAction, waitSeconds ...int) error {
if s.powerLock == nil {
s.powerLock = semaphore.NewWeighted(1)
}
// Only attempt to acquire a lock on the process if this is not a termination event. We want to
// just allow those events to pass right through for good reason. If a server is currently trying
// to process a power action but has gotten stuck you still should be able to pass through the
// terminate event. The good news here is that doing that oftentimes will get the stuck process to
// move again, and naturally continue through the process.
if action != PowerActionTerminate {
// Determines if we should wait for the lock or not. If a value greater than 0 is passed
// into this function we will wait that long for a lock to be acquired.
if len(waitSeconds) > 0 && waitSeconds[0] != 0 {
ctx, _ := context.WithTimeout(context.Background(), time.Second*time.Duration(waitSeconds[0]))
// Attempt to acquire a lock on the power action lock for up to 30 seconds. If more
// time than that passes an error will be propagated back up the chain and this
// request will be aborted.
if err := s.powerLock.Acquire(ctx, 1); err != nil {
return errors.Wrap(err, "could not acquire lock on power state")
}
} else {
// If no wait duration was provided we will attempt to immediately acquire the lock
// and bail out with a context deadline error if it is not acquired immediately.
if ok := s.powerLock.TryAcquire(1); !ok {
return errors.Wrap(context.DeadlineExceeded, "could not acquire lock on power state")
}
}
// Release the lock once the process being requested has finished executing.
defer s.powerLock.Release(1)
} else {
// Still try to acquire the lock if terminating and it is available, just so that other power
// actions are blocked until it has completed. However, if it is unavailable we won't stop
// the entire process.
if ok := s.powerLock.TryAcquire(1); ok {
// If we managed to acquire the lock be sure to released it once this process is completed.
defer s.powerLock.Release(1)
}
}
switch action {
case PowerActionStart:
// Run the pre-boot logic for the server before processing the environment start.
if err := s.onBeforeStart(); err != nil {
return err
}
return s.Environment.Start()
case PowerActionStop:
// We're specificially waiting for the process to be stopped here, otherwise the lock is released
// too soon, and you can rack up all sorts of issues.
return s.Environment.WaitForStop(10*60, true)
case PowerActionRestart:
if err := s.Environment.WaitForStop(10*60, true); err != nil {
// Even timeout errors should be bubbled back up the stack. If the process didn't stop
// nicely, but the terminate argument was passed then the server is stopped without an
// error being returned.
//
// However, if terminate is not passed you'll get a context deadline error. We could
// probably handle that nicely here, but I'd rather just pass it back up the stack for now.
// Either way, any type of error indicates we should not attempt to start the server back
// up.
return err
}
// Now actually try to start the process by executing the normal pre-boot logic.
if err := s.onBeforeStart(); err != nil {
return err
}
return s.Environment.Start()
case PowerActionTerminate:
return s.Environment.Terminate(os.Kill)
}
return errors.New("attempting to handle unknown power action")
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}
// Execute a few functions before actually calling the environment start commands. This ensures
// that everything is ready to go for environment booting, and that the server can even be started.
func (s *Server) onBeforeStart() error {
// Disallow start & restart if the server is suspended.
if s.IsSuspended() {
return new(suspendedError)
}
s.Log().Info("syncing server configuration with panel")
if err := s.Sync(); err != nil {
return errors.Wrap(err, "unable to sync server data from Panel instance")
}
if !s.Filesystem.HasSpaceAvailable() {
return errors.New("cannot start server, not enough disk space available")
}
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// Update the configuration files defined for the server before beginning the boot process.
// This process executes a bunch of parallel updates, so we just block until that process
// is completee. Any errors as a result of this will just be bubbled out in the logger,
// we don't need to actively do anything about it at this point, worst comes to worst the
// server starts in a weird state and the user can manually adjust.
s.PublishConsoleOutputFromDaemon("Updating process configuration files...")
s.UpdateConfigurationFiles()
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s.PublishConsoleOutputFromDaemon("Ensuring file permissions are set correctly, this could take a few seconds...")
// Ensure all of the server file permissions are set correctly before booting the process.
if err := s.Filesystem.Chown("/"); err != nil {
return errors.Wrap(err, "failed to chown root server directory during pre-boot process")
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}
return nil
}