chore: vendor

vendor/google.golang.org/grpc/internal/idle/idle.go

@@ -0,0 +1,278 @@
+/*
+ *
+ * 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 idle contains a component for managing idleness (entering and exiting)
+// based on RPC activity.
+package idle
+
+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)
+}
+
+// Enforcer is the functionality provided by grpc.ClientConn to enter
+// and exit from idle mode.
+type Enforcer interface {
+	ExitIdleMode() error
+	EnterIdleMode()
+}
+
+// Manager implements idleness detection and calls the configured Enforcer to
+// enter/exit idle mode when appropriate.  Must be created by NewManager.
+type Manager 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 Enforcer // Functionality provided by grpc.ClientConn.
+	timeout  time.Duration
+
+	// 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
+}
+
+// NewManager creates a new idleness manager implementation for the
+// given idle timeout.  It begins in idle mode.
+func NewManager(enforcer Enforcer, timeout time.Duration) *Manager {
+	return &Manager{
+		enforcer:         enforcer,
+		timeout:          timeout,
+		actuallyIdle:     true,
+		activeCallsCount: -math.MaxInt32,
+	}
+}
+
+// resetIdleTimerLocked resets the idle timer to the given duration.  Called
+// when exiting idle mode or when the timer fires and we need to reset it.
+func (m *Manager) resetIdleTimerLocked(d time.Duration) {
+	if m.isClosed() || m.timeout == 0 || m.actuallyIdle {
+		return
+	}
+
+	// It is safe to ignore the return value from Reset() because this method is
+	// only ever called from the timer callback or when exiting idle mode.
+	if m.timer != nil {
+		m.timer.Stop()
+	}
+	m.timer = timeAfterFunc(d, m.handleIdleTimeout)
+}
+
+func (m *Manager) resetIdleTimer(d time.Duration) {
+	m.idleMu.Lock()
+	defer m.idleMu.Unlock()
+	m.resetIdleTimerLocked(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 (m *Manager) handleIdleTimeout() {
+	if m.isClosed() {
+		return
+	}
+
+	if atomic.LoadInt32(&m.activeCallsCount) > 0 {
+		m.resetIdleTimer(m.timeout)
+		return
+	}
+
+	// There has been activity on the channel since we last got here. Reset the
+	// timer and return.
+	if atomic.LoadInt32(&m.activeSinceLastTimerCheck) == 1 {
+		// Set the timer to fire after a duration of idle timeout, calculated
+		// from the time the most recent RPC completed.
+		atomic.StoreInt32(&m.activeSinceLastTimerCheck, 0)
+		m.resetIdleTimer(time.Duration(atomic.LoadInt64(&m.lastCallEndTime)-time.Now().UnixNano()) + m.timeout)
+		return
+	}
+
+	// Now that we've checked that there has been no activity, attempt to enter
+	// idle mode, which is very likely to succeed.
+	if m.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.
+	m.resetIdleTimer(m.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 (m *Manager) tryEnterIdleMode() bool {
+	// 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(&m.activeCallsCount, 0, -math.MaxInt32) {
+		// This CAS operation can fail if an RPC started after we checked for
+		// activity in the timer handler, or one was ongoing from before the
+		// last time the timer fired, or if a test is attempting to enter idle
+		// mode without checking.  In all cases, abort going into idle mode.
+		return false
+	}
+	// N.B. if we fail to enter idle mode after this, we must re-add
+	// math.MaxInt32 to m.activeCallsCount.
+
+	m.idleMu.Lock()
+	defer m.idleMu.Unlock()
+
+	if atomic.LoadInt32(&m.activeCallsCount) != -math.MaxInt32 {
+		// We raced and lost to a new RPC. Very rare, but stop entering idle.
+		atomic.AddInt32(&m.activeCallsCount, math.MaxInt32)
+		return false
+	}
+	if atomic.LoadInt32(&m.activeSinceLastTimerCheck) == 1 {
+		// A 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.
+		atomic.AddInt32(&m.activeCallsCount, math.MaxInt32)
+		return false
+	}
+
+	// No new RPCs have come in since we set the active calls count value to
+	// -math.MaxInt32. And since we have the lock, it is safe to enter idle mode
+	// unconditionally now.
+	m.enforcer.EnterIdleMode()
+	m.actuallyIdle = true
+	return true
+}
+
+func (m *Manager) EnterIdleModeForTesting() {
+	m.tryEnterIdleMode()
+}
+
+// OnCallBegin is invoked at the start of every RPC.
+func (m *Manager) OnCallBegin() error {
+	if m.isClosed() {
+		return nil
+	}
+
+	if atomic.AddInt32(&m.activeCallsCount, 1) > 0 {
+		// Channel is not idle now. Set the activity bit and allow the call.
+		atomic.StoreInt32(&m.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 := m.ExitIdleMode(); err != nil {
+		// Undo the increment to calls count, and return an error causing the
+		// RPC to fail.
+		atomic.AddInt32(&m.activeCallsCount, -1)
+		return err
+	}
+
+	atomic.StoreInt32(&m.activeSinceLastTimerCheck, 1)
+	return nil
+}
+
+// ExitIdleMode instructs m to call the enforcer's ExitIdleMode and update m's
+// internal state.
+func (m *Manager) ExitIdleMode() error {
+	// Holds idleMu which ensures mutual exclusion with tryEnterIdleMode.
+	m.idleMu.Lock()
+	defer m.idleMu.Unlock()
+
+	if m.isClosed() || !m.actuallyIdle {
+		// This can happen in three 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.
+		// - Channel is not in idle mode, and the user calls Connect which calls
+		//   m.ExitIdleMode.
+		//
+		// In any case, there is nothing to do here.
+		return nil
+	}
+
+	if err := m.enforcer.ExitIdleMode(); err != nil {
+		return fmt.Errorf("failed to exit idle mode: %w", err)
+	}
+
+	// Undo the idle entry process. This also respects any new RPC attempts.
+	atomic.AddInt32(&m.activeCallsCount, math.MaxInt32)
+	m.actuallyIdle = false
+
+	// Start a new timer to fire after the configured idle timeout.
+	m.resetIdleTimerLocked(m.timeout)
+	return nil
+}
+
+// OnCallEnd is invoked at the end of every RPC.
+func (m *Manager) OnCallEnd() {
+	if m.isClosed() {
+		return
+	}
+
+	// Record the time at which the most recent call finished.
+	atomic.StoreInt64(&m.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(&m.activeCallsCount, -1)
+}
+
+func (m *Manager) isClosed() bool {
+	return atomic.LoadInt32(&m.closed) == 1
+}
+
+func (m *Manager) Close() {
+	atomic.StoreInt32(&m.closed, 1)
+
+	m.idleMu.Lock()
+	if m.timer != nil {
+		m.timer.Stop()
+		m.timer = nil
+	}
+	m.idleMu.Unlock()
+}