| 1 | package calendar |
| 2 | |
| 3 | import ( |
| 4 | "context" |
| 5 | "errors" |
| 6 | "net/http" |
| 7 | "sync" |
| 8 | "time" |
| 9 | |
| 10 | "amadan.net/rastrillo/rastrillo/carlos" |
| 11 | ) |
| 12 | |
| 13 | const scheduledWorkName = "calendar-next-due" |
| 14 | |
| 15 | type scheduledWork struct { |
| 16 | mu sync.Mutex |
| 17 | lifeMu sync.Mutex |
| 18 | started, closed bool |
| 19 | finishOnce sync.Once |
| 20 | ctx context.Context |
| 21 | cancel context.CancelFunc |
| 22 | done chan struct{} |
| 23 | wake chan struct{} |
| 24 | query func(context.Context) (time.Time, error) |
| 25 | put func(context.Context, string, time.Time, string) error |
| 26 | remove func(context.Context, string) error |
| 27 | capability func(context.Context) error |
| 28 | armed func(context.Context) (remoteSchedule, error) |
| 29 | now func() time.Time |
| 30 | report func(error) |
| 31 | development bool |
| 32 | known bool |
| 33 | registered time.Time |
| 34 | registeredAt time.Time |
| 35 | rawDue time.Time |
| 36 | observed time.Time |
| 37 | force bool |
| 38 | allowRestore bool |
| 39 | failures int |
| 40 | notBefore time.Time |
| 41 | checked time.Time |
| 42 | retryDelay time.Duration |
| 43 | reconcileEvery time.Duration |
| 44 | } |
| 45 | |
| 46 | func newScheduledWork(query func(context.Context) (time.Time, error), development bool, report func(error)) *scheduledWork { |
| 47 | ctx, cancel := context.WithCancel(context.Background()) |
| 48 | return &scheduledWork{ctx: ctx, cancel: cancel, done: make(chan struct{}), wake: make(chan struct{}, 1), query: query, |
| 49 | put: carlos.ScheduleAt, remove: carlos.ScheduleCancel, capability: scheduleCapability, armed: scheduleArmed, now: time.Now, |
| 50 | report: report, development: development, retryDelay: time.Second, reconcileEvery: time.Minute, allowRestore: true} |
| 51 | } |
| 52 | |
| 53 | func (s *scheduledWork) start() error { |
| 54 | s.lifeMu.Lock() |
| 55 | defer s.lifeMu.Unlock() |
| 56 | if s.closed { |
| 57 | return context.Canceled |
| 58 | } |
| 59 | if s.started { |
| 60 | return nil |
| 61 | } |
| 62 | s.started = true |
| 63 | if _, err := s.sync(true); err != nil && permanentScheduleError(err) { |
| 64 | s.cancel() |
| 65 | s.finishOnce.Do(func() { close(s.done) }) |
| 66 | return err |
| 67 | } |
| 68 | go s.retry() |
| 69 | return nil |
| 70 | } |
| 71 | |
| 72 | func (s *scheduledWork) close() { |
| 73 | s.cancel() |
| 74 | s.lifeMu.Lock() |
| 75 | s.closed = true |
| 76 | if !s.started { |
| 77 | s.finishOnce.Do(func() { close(s.done) }) |
| 78 | } |
| 79 | s.lifeMu.Unlock() |
| 80 | <-s.done |
| 81 | s.mu.Lock() |
| 82 | s.mu.Unlock() |
| 83 | } |
| 84 | |
| 85 | func (s *scheduledWork) request() { |
| 86 | select { |
| 87 | case s.wake <- struct{}{}: |
| 88 | default: |
| 89 | } |
| 90 | } |
| 91 | |
| 92 | func (s *scheduledWork) sync(force bool) (time.Time, error) { |
| 93 | due, err := s.synchronize(force, false) |
| 94 | if err != nil { |
| 95 | s.request() |
| 96 | } |
| 97 | return due, err |
| 98 | } |
| 99 | |
| 100 | func (s *scheduledWork) finishDrain(start time.Time, progress int, drainErr error) error { |
| 101 | s.mu.Lock() |
| 102 | s.allowRestore = false |
| 103 | ctx, cancel := context.WithTimeout(s.ctx, 2*time.Second) |
| 104 | due, queryErr := s.query(ctx) |
| 105 | cancel() |
| 106 | if queryErr != nil { |
| 107 | due = s.rawDue |
| 108 | } |
| 109 | failed := drainErr != nil || queryErr != nil || (progress == 0 && !due.IsZero() && !due.After(start)) |
| 110 | if !failed { |
| 111 | s.failures = 0 |
| 112 | s.notBefore = time.Time{} |
| 113 | } else { |
| 114 | s.failures = min(s.failures+1, 5) |
| 115 | delay := min(time.Minute<<(s.failures-1), 15*time.Minute) |
| 116 | if !due.IsZero() { |
| 117 | delay = max(delay, min(max(s.now().Sub(due)/4, time.Minute), 15*time.Minute)) |
| 118 | } |
| 119 | s.notBefore = s.now().Add(delay) |
| 120 | } |
| 121 | s.mu.Unlock() |
| 122 | _, err := s.sync(true) |
| 123 | if queryErr != nil { |
| 124 | return queryErr |
| 125 | } |
| 126 | return err |
| 127 | } |
| 128 | |
| 129 | func (s *scheduledWork) synchronize(force, inspect bool) (due time.Time, err error) { |
| 130 | s.mu.Lock() |
| 131 | defer s.mu.Unlock() |
| 132 | ctx, cancel := context.WithTimeout(s.ctx, 4*time.Second) |
| 133 | defer cancel() |
| 134 | return s.synchronizeLocked(ctx, force, inspect) |
| 135 | } |
| 136 | |
| 137 | func (s *scheduledWork) synchronizeLocked(ctx context.Context, force, inspect bool) (due time.Time, err error) { |
| 138 | if err := ctx.Err(); err != nil { |
| 139 | return s.observed, err |
| 140 | } |
| 141 | s.force = s.force || force |
| 142 | attempted := false |
| 143 | defer func() { |
| 144 | if err != nil { |
| 145 | s.force = s.force || attempted |
| 146 | if s.report != nil { |
| 147 | s.report(err) |
| 148 | } |
| 149 | } |
| 150 | }() |
| 151 | queryCtx, cancel := context.WithTimeout(ctx, 2*time.Second) |
| 152 | due, err = s.query(queryCtx) |
| 153 | cancel() |
| 154 | if err != nil { |
| 155 | return s.observed, err |
| 156 | } |
| 157 | s.rawDue = due |
| 158 | if !s.known && s.allowRestore { |
| 159 | if restored, restoreErr := s.restore(ctx, due); restoreErr != nil { |
| 160 | return due, restoreErr |
| 161 | } else if restored { |
| 162 | return s.observed, nil |
| 163 | } |
| 164 | } |
| 165 | if !s.notBefore.IsZero() && (due.IsZero() || due.Before(s.notBefore)) { |
| 166 | due = s.notBefore |
| 167 | } |
| 168 | s.observed = due |
| 169 | if s.known && !s.force && due.Equal(s.registered) { |
| 170 | if !inspect && s.now().Sub(s.checked) < s.reconcileEvery { |
| 171 | return due, nil |
| 172 | } |
| 173 | controlCtx, cancel := context.WithTimeout(ctx, 2*time.Second) |
| 174 | var armed remoteSchedule |
| 175 | armed, err = s.armed(controlCtx) |
| 176 | cancel() |
| 177 | if errors.Is(err, carlos.ErrNotOnCarlos) && s.development { |
| 178 | err = nil |
| 179 | armed = remoteSchedule{NextAt: s.registeredAt.Unix(), DueAt: s.registeredAt.Unix(), Path: "/jobs/reminders", Kind: "once"} |
| 180 | } |
| 181 | if err != nil { |
| 182 | return due, err |
| 183 | } |
| 184 | s.checked = s.now() |
| 185 | if due.IsZero() || s.matches(armed) { |
| 186 | return due, nil |
| 187 | } |
| 188 | s.force = true |
| 189 | } |
| 190 | capabilityCtx, cancel := context.WithTimeout(ctx, 2*time.Second) |
| 191 | err = s.capability(capabilityCtx) |
| 192 | cancel() |
| 193 | if errors.Is(err, carlos.ErrNotOnCarlos) && s.development { |
| 194 | err = nil |
| 195 | } else if err != nil { |
| 196 | return due, err |
| 197 | } |
| 198 | controlCtx, cancel := context.WithTimeout(ctx, 2*time.Second) |
| 199 | defer cancel() |
| 200 | attempted = true |
| 201 | if due.IsZero() { |
| 202 | err = s.remove(controlCtx, scheduledWorkName) |
| 203 | } else { |
| 204 | at := due |
| 205 | now := s.now() |
| 206 | if at.Before(now) || at.Unix() <= 0 { |
| 207 | at = now |
| 208 | } |
| 209 | if latest := now.Add(carlos.MaxAhead - time.Minute); at.After(latest) { |
| 210 | at = latest |
| 211 | } |
| 212 | err = s.put(controlCtx, scheduledWorkName, at, "/jobs/reminders") |
| 213 | if err == nil { |
| 214 | s.registeredAt = time.Unix(at.Unix(), 0) |
| 215 | } |
| 216 | } |
| 217 | if errors.Is(err, carlos.ErrNotOnCarlos) && s.development { |
| 218 | err = nil |
| 219 | } |
| 220 | if err == nil { |
| 221 | s.known, s.force = true, false |
| 222 | s.registered = due |
| 223 | s.checked = s.now() |
| 224 | } |
| 225 | return due, err |
| 226 | } |
| 227 | |
| 228 | func (s *scheduledWork) retry() { |
| 229 | defer s.finishOnce.Do(func() { close(s.done) }) |
| 230 | timer := time.NewTimer(s.reconcileEvery) |
| 231 | defer timer.Stop() |
| 232 | retrying := false |
| 233 | delay := s.retryDelay |
| 234 | for { |
| 235 | inspect := false |
| 236 | select { |
| 237 | case <-s.ctx.Done(): |
| 238 | return |
| 239 | case <-s.wake: |
| 240 | if retrying { |
| 241 | continue |
| 242 | } |
| 243 | case <-timer.C: |
| 244 | inspect = !retrying |
| 245 | } |
| 246 | _, err := s.synchronize(false, inspect) |
| 247 | if err != nil { |
| 248 | retrying = true |
| 249 | timer.Reset(delay) |
| 250 | delay = min(delay*2, 30*time.Second) |
| 251 | } else { |
| 252 | retrying = false |
| 253 | delay = s.retryDelay |
| 254 | timer.Reset(s.reconcileEvery) |
| 255 | } |
| 256 | } |
| 257 | } |
| 258 | |
| 259 | func (s *scheduledWork) middleware(next http.Handler) http.Handler { |
| 260 | return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { |
| 261 | defer s.request() |
| 262 | next.ServeHTTP(w, r) |
| 263 | }) |
| 264 | } |
| 265 | |
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