diff options
Diffstat (limited to 'vendor/google.golang.org/grpc/idle.go')
| -rw-r--r-- | vendor/google.golang.org/grpc/idle.go | 287 |
1 files changed, 287 insertions, 0 deletions
diff --git a/vendor/google.golang.org/grpc/idle.go b/vendor/google.golang.org/grpc/idle.go new file mode 100644 index 000000000..dc3dc72f6 --- /dev/null +++ b/vendor/google.golang.org/grpc/idle.go @@ -0,0 +1,287 @@ +/* + * + * Copyright 2023 gRPC authors. + * + * Licensed under the Apache License, Version 2.0 (the "License"); + * you may not use this file except in compliance with the License. + * You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + * + */ + +package grpc + +import ( + "fmt" + "math" + "sync" + "sync/atomic" + "time" +) + +// For overriding in unit tests. +var timeAfterFunc = func(d time.Duration, f func()) *time.Timer { + return time.AfterFunc(d, f) +} + +// idlenessEnforcer is the functionality provided by grpc.ClientConn to enter +// and exit from idle mode. +type idlenessEnforcer interface { + exitIdleMode() error + enterIdleMode() error +} + +// idlenessManager defines the functionality required to track RPC activity on a +// channel. +type idlenessManager interface { + onCallBegin() error + onCallEnd() + close() +} + +type noopIdlenessManager struct{} + +func (noopIdlenessManager) onCallBegin() error { return nil } +func (noopIdlenessManager) onCallEnd() {} +func (noopIdlenessManager) close() {} + +// idlenessManagerImpl implements the idlenessManager interface. It uses atomic +// operations to synchronize access to shared state and a mutex to guarantee +// mutual exclusion in a critical section. +type idlenessManagerImpl struct { + // State accessed atomically. + lastCallEndTime int64 // Unix timestamp in nanos; time when the most recent RPC completed. + activeCallsCount int32 // Count of active RPCs; -math.MaxInt32 means channel is idle or is trying to get there. + activeSinceLastTimerCheck int32 // Boolean; True if there was an RPC since the last timer callback. + closed int32 // Boolean; True when the manager is closed. + + // Can be accessed without atomics or mutex since these are set at creation + // time and read-only after that. + enforcer idlenessEnforcer // Functionality provided by grpc.ClientConn. + timeout int64 // Idle timeout duration nanos stored as an int64. + + // idleMu is used to guarantee mutual exclusion in two scenarios: + // - Opposing intentions: + // - a: Idle timeout has fired and handleIdleTimeout() is trying to put + // the channel in idle mode because the channel has been inactive. + // - b: At the same time an RPC is made on the channel, and onCallBegin() + // is trying to prevent the channel from going idle. + // - Competing intentions: + // - The channel is in idle mode and there are multiple RPCs starting at + // the same time, all trying to move the channel out of idle. Only one + // of them should succeed in doing so, while the other RPCs should + // piggyback on the first one and be successfully handled. + idleMu sync.RWMutex + actuallyIdle bool + timer *time.Timer +} + +// newIdlenessManager creates a new idleness manager implementation for the +// given idle timeout. +func newIdlenessManager(enforcer idlenessEnforcer, idleTimeout time.Duration) idlenessManager { + if idleTimeout == 0 { + return noopIdlenessManager{} + } + + i := &idlenessManagerImpl{ + enforcer: enforcer, + timeout: int64(idleTimeout), + } + i.timer = timeAfterFunc(idleTimeout, i.handleIdleTimeout) + return i +} + +// resetIdleTimer resets the idle timer to the given duration. This method +// should only be called from the timer callback. +func (i *idlenessManagerImpl) resetIdleTimer(d time.Duration) { + i.idleMu.Lock() + defer i.idleMu.Unlock() + + if i.timer == nil { + // Only close sets timer to nil. We are done. + return + } + + // It is safe to ignore the return value from Reset() because this method is + // only ever called from the timer callback, which means the timer has + // already fired. + i.timer.Reset(d) +} + +// handleIdleTimeout is the timer callback that is invoked upon expiry of the +// configured idle timeout. The channel is considered inactive if there are no +// ongoing calls and no RPC activity since the last time the timer fired. +func (i *idlenessManagerImpl) handleIdleTimeout() { + if i.isClosed() { + return + } + + if atomic.LoadInt32(&i.activeCallsCount) > 0 { + i.resetIdleTimer(time.Duration(i.timeout)) + return + } + + // There has been activity on the channel since we last got here. Reset the + // timer and return. + if atomic.LoadInt32(&i.activeSinceLastTimerCheck) == 1 { + // Set the timer to fire after a duration of idle timeout, calculated + // from the time the most recent RPC completed. + atomic.StoreInt32(&i.activeSinceLastTimerCheck, 0) + i.resetIdleTimer(time.Duration(atomic.LoadInt64(&i.lastCallEndTime) + i.timeout - time.Now().UnixNano())) + return + } + + // This CAS operation is extremely likely to succeed given that there has + // been no activity since the last time we were here. Setting the + // activeCallsCount to -math.MaxInt32 indicates to onCallBegin() that the + // channel is either in idle mode or is trying to get there. + if !atomic.CompareAndSwapInt32(&i.activeCallsCount, 0, -math.MaxInt32) { + // This CAS operation can fail if an RPC started after we checked for + // activity at the top of this method, or one was ongoing from before + // the last time we were here. In both case, reset the timer and return. + i.resetIdleTimer(time.Duration(i.timeout)) + return + } + + // Now that we've set the active calls count to -math.MaxInt32, it's time to + // actually move to idle mode. + if i.tryEnterIdleMode() { + // Successfully entered idle mode. No timer needed until we exit idle. + return + } + + // Failed to enter idle mode due to a concurrent RPC that kept the channel + // active, or because of an error from the channel. Undo the attempt to + // enter idle, and reset the timer to try again later. + atomic.AddInt32(&i.activeCallsCount, math.MaxInt32) + i.resetIdleTimer(time.Duration(i.timeout)) +} + +// tryEnterIdleMode instructs the channel to enter idle mode. But before +// that, it performs a last minute check to ensure that no new RPC has come in, +// making the channel active. +// +// Return value indicates whether or not the channel moved to idle mode. +// +// Holds idleMu which ensures mutual exclusion with exitIdleMode. +func (i *idlenessManagerImpl) tryEnterIdleMode() bool { + i.idleMu.Lock() + defer i.idleMu.Unlock() + + if atomic.LoadInt32(&i.activeCallsCount) != -math.MaxInt32 { + // We raced and lost to a new RPC. Very rare, but stop entering idle. + return false + } + if atomic.LoadInt32(&i.activeSinceLastTimerCheck) == 1 { + // An very short RPC could have come in (and also finished) after we + // checked for calls count and activity in handleIdleTimeout(), but + // before the CAS operation. So, we need to check for activity again. + return false + } + + // No new RPCs have come in since we last set the active calls count value + // -math.MaxInt32 in the timer callback. And since we have the lock, it is + // safe to enter idle mode now. + if err := i.enforcer.enterIdleMode(); err != nil { + logger.Errorf("Failed to enter idle mode: %v", err) + return false + } + + // Successfully entered idle mode. + i.actuallyIdle = true + return true +} + +// onCallBegin is invoked at the start of every RPC. +func (i *idlenessManagerImpl) onCallBegin() error { + if i.isClosed() { + return nil + } + + if atomic.AddInt32(&i.activeCallsCount, 1) > 0 { + // Channel is not idle now. Set the activity bit and allow the call. + atomic.StoreInt32(&i.activeSinceLastTimerCheck, 1) + return nil + } + + // Channel is either in idle mode or is in the process of moving to idle + // mode. Attempt to exit idle mode to allow this RPC. + if err := i.exitIdleMode(); err != nil { + // Undo the increment to calls count, and return an error causing the + // RPC to fail. + atomic.AddInt32(&i.activeCallsCount, -1) + return err + } + + atomic.StoreInt32(&i.activeSinceLastTimerCheck, 1) + return nil +} + +// exitIdleMode instructs the channel to exit idle mode. +// +// Holds idleMu which ensures mutual exclusion with tryEnterIdleMode. +func (i *idlenessManagerImpl) exitIdleMode() error { + i.idleMu.Lock() + defer i.idleMu.Unlock() + + if !i.actuallyIdle { + // This can happen in two scenarios: + // - handleIdleTimeout() set the calls count to -math.MaxInt32 and called + // tryEnterIdleMode(). But before the latter could grab the lock, an RPC + // came in and onCallBegin() noticed that the calls count is negative. + // - Channel is in idle mode, and multiple new RPCs come in at the same + // time, all of them notice a negative calls count in onCallBegin and get + // here. The first one to get the lock would got the channel to exit idle. + // + // Either way, nothing to do here. + return nil + } + + if err := i.enforcer.exitIdleMode(); err != nil { + return fmt.Errorf("channel failed to exit idle mode: %v", err) + } + + // Undo the idle entry process. This also respects any new RPC attempts. + atomic.AddInt32(&i.activeCallsCount, math.MaxInt32) + i.actuallyIdle = false + + // Start a new timer to fire after the configured idle timeout. + i.timer = timeAfterFunc(time.Duration(i.timeout), i.handleIdleTimeout) + return nil +} + +// onCallEnd is invoked at the end of every RPC. +func (i *idlenessManagerImpl) onCallEnd() { + if i.isClosed() { + return + } + + // Record the time at which the most recent call finished. + atomic.StoreInt64(&i.lastCallEndTime, time.Now().UnixNano()) + + // Decrement the active calls count. This count can temporarily go negative + // when the timer callback is in the process of moving the channel to idle + // mode, but one or more RPCs come in and complete before the timer callback + // can get done with the process of moving to idle mode. + atomic.AddInt32(&i.activeCallsCount, -1) +} + +func (i *idlenessManagerImpl) isClosed() bool { + return atomic.LoadInt32(&i.closed) == 1 +} + +func (i *idlenessManagerImpl) close() { + atomic.StoreInt32(&i.closed, 1) + + i.idleMu.Lock() + i.timer.Stop() + i.timer = nil + i.idleMu.Unlock() +} |