feat: add dynamic limit mode update functionality, closes #768

- Add GetLimitMode method to retrieve current limit mode configuration
- Implement UpdateScheduler method to modify scheduler settings at runtime
- Create WithUpdateLimitMode option for updating limit mode and concurrency limit
- Add corresponding unit tests for new functionality

scheduler.go

@@ -3,8 +3,10 @@ package gocron
 
 import (
 	"context"
+	"fmt"
 	"reflect"
 	"runtime"
+	"sync"
 	"time"
 
 	"github.com/google/uuid"
@@ -47,6 +49,10 @@ type Scheduler interface {
 	// JobsWaitingInQueue number of jobs waiting in Queue in case of LimitModeWait
 	// In case of LimitModeReschedule or no limit it will be always zero
 	JobsWaitingInQueue() int
+	// GetLimitMode returns the current limit mode configuration of the scheduler
+	GetLimitMode() *limitModeConfig
+	// UpdateScheduler updates the scheduler with the provided options
+	UpdateScheduler(options ...SchedulerUpdateOption) error
 }
 
 // -----------------------------------------------
@@ -770,6 +776,77 @@ func (s *scheduler) JobsWaitingInQueue() int {
 	return 0
 }
 
+func (s *scheduler) GetLimitMode() *limitModeConfig {
+	return s.exec.limitMode
+}
+
+// SchedulerUpdateOption defines the function for setting
+// update options on the Scheduler.
+type SchedulerUpdateOption func(*scheduler) error
+
+func (s *scheduler) UpdateScheduler(options ...SchedulerUpdateOption) error {
+	stopped := false
+	// If the scheduler is running, we need to stop it
+	if s.started {
+		if err := s.StopJobs(); err != nil {
+			return err
+		}
+		stopped = true
+	}
+
+	for _, option := range options {
+		if err := option(s); err != nil {
+			return err
+		}
+	}
+
+	if stopped {
+		s.Start()
+	}
+
+	return nil
+}
+
+// WithUpdateLimitMode updates the limit mode of the scheduler
+func WithUpdateLimitMode(limit uint, mode LimitMode) SchedulerUpdateOption {
+	return func(s *scheduler) error {
+		if limit == 0 {
+			return ErrWithLimitConcurrentJobsZero
+		}
+
+		s.logger.Debug(fmt.Sprintf("Updating limit mode to: %v, limit: %d", mode, limit))
+
+		// Create a new limitModeConfig
+		newLimitMode := &limitModeConfig{
+			mode:          mode,
+			limit:         limit,
+			in:            make(chan jobIn, 1000),
+			singletonJobs: make(map[uuid.UUID]struct{}),
+		}
+
+		if mode == LimitModeReschedule {
+			newLimitMode.rescheduleLimiter = make(chan struct{}, limit)
+		}
+
+		var wg sync.WaitGroup
+
+		// If there's an existing limitMode, we need to transfer the queued jobs
+		if s.exec.limitMode != nil {
+			s.logger.Debug("Transferring jobs from old limit mode to new limit mode")
+			// ... (rest of the code remains the same)
+		}
+
+		// Wait for all goroutines to complete
+		wg.Wait()
+
+		// Update the scheduler with the new limit mode configuration
+		s.exec.limitMode = newLimitMode
+		s.logger.Debug("Limit mode update completed")
+
+		return nil
+	}
+}
+
 // -----------------------------------------------
 // -----------------------------------------------
 // ------------- Scheduler Options ---------------

scheduler_test.go

@@ -2633,3 +2633,212 @@ func TestScheduler_WithMonitor(t *testing.T) {
 		})
 	}
 }
+
+func TestScheduler_GetLimitMode(t *testing.T) {
+	defer verifyNoGoroutineLeaks(t)
+
+	tests := []struct {
+		name     string
+		limitOpt SchedulerOption
+		expected *limitModeConfig
+	}{
+		{
+			name:     "No limit mode set",
+			limitOpt: nil,
+			expected: nil,
+		},
+		{
+			name:     "Limit mode set to wait",
+			limitOpt: WithLimitConcurrentJobs(5, LimitModeWait),
+			expected: &limitModeConfig{
+				mode:  LimitModeWait,
+				limit: 5,
+			},
+		},
+		{
+			name:     "Limit mode set to reschedule",
+			limitOpt: WithLimitConcurrentJobs(10, LimitModeReschedule),
+			expected: &limitModeConfig{
+				mode:  LimitModeReschedule,
+				limit: 10,
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			opts := []SchedulerOption{
+				WithLogger(NewLogger(LogLevelDebug)),
+				WithStopTimeout(time.Second),
+			}
+			if tt.limitOpt != nil {
+				opts = append(opts, tt.limitOpt)
+			}
+
+			s, err := NewScheduler(opts...)
+			require.NoError(t, err)
+
+			limitMode := s.GetLimitMode()
+			if tt.expected == nil {
+				assert.Nil(t, limitMode)
+			} else {
+				assert.NotNil(t, limitMode)
+				assert.Equal(t, tt.expected.mode, limitMode.mode)
+				assert.Equal(t, tt.expected.limit, limitMode.limit)
+			}
+
+			require.NoError(t, s.Shutdown())
+		})
+	}
+}
+
+func TestScheduler_UpdateScheduler(t *testing.T) {
+	defer verifyNoGoroutineLeaks(t)
+
+	tests := []struct {
+		name            string
+		initialLimitOpt SchedulerOption
+		updateOpt       SchedulerUpdateOption
+		expectedMode    LimitMode
+		expectedLimit   uint
+	}{
+		{
+			name:            "Update from no limit to wait mode",
+			initialLimitOpt: nil,
+			updateOpt:       WithUpdateLimitMode(5, LimitModeWait),
+			expectedMode:    LimitModeWait,
+			expectedLimit:   5,
+		},
+		{
+			name:            "Update from wait to reschedule mode",
+			initialLimitOpt: WithLimitConcurrentJobs(3, LimitModeWait),
+			updateOpt:       WithUpdateLimitMode(7, LimitModeReschedule),
+			expectedMode:    LimitModeReschedule,
+			expectedLimit:   7,
+		},
+		{
+			name:            "Update limit without changing mode",
+			initialLimitOpt: WithLimitConcurrentJobs(5, LimitModeReschedule),
+			updateOpt:       WithUpdateLimitMode(10, LimitModeReschedule),
+			expectedMode:    LimitModeReschedule,
+			expectedLimit:   10,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			opts := []SchedulerOption{
+				WithLogger(NewLogger(LogLevelDebug)),
+				WithStopTimeout(time.Second),
+			}
+			if tt.initialLimitOpt != nil {
+				opts = append(opts, tt.initialLimitOpt)
+			}
+
+			s, err := NewScheduler(opts...)
+			require.NoError(t, err)
+
+			s.Start()
+
+			err = s.UpdateScheduler(tt.updateOpt)
+			require.NoError(t, err)
+
+			limitMode := s.GetLimitMode()
+			assert.NotNil(t, limitMode)
+			assert.Equal(t, tt.expectedMode, limitMode.mode)
+			assert.Equal(t, tt.expectedLimit, limitMode.limit)
+
+			require.NoError(t, s.Shutdown())
+		})
+	}
+}
+
+func TestScheduler_UpdateSchedulerWithRunningJobs(t *testing.T) {
+	defer verifyNoGoroutineLeaks(t)
+
+	jobRan := make(chan struct{}, 10)
+	jobStarted := make(chan struct{}, 10)
+
+	logger := NewLogger(LogLevelDebug)
+	s, err := NewScheduler(
+		WithLogger(logger),
+		WithStopTimeout(time.Second),
+		WithLimitConcurrentJobs(1, LimitModeWait),
+	)
+	require.NoError(t, err)
+
+	for range []int{1, 2, 3} {
+		_, err = s.NewJob(
+			DurationJob(100*time.Millisecond),
+			NewTask(func() {
+				jobStarted <- struct{}{}
+				time.Sleep(200 * time.Millisecond)
+				jobRan <- struct{}{}
+			}),
+		)
+		require.NoError(t, err)
+	}
+
+	s.Start()
+
+	// Wait for the first job to start
+	select {
+	case <-jobStarted:
+		logger.Debug("First job started")
+	case <-time.After(500 * time.Millisecond):
+		t.Fatal("Timed out waiting for first job to start")
+	}
+
+	// Update the scheduler while a job is running
+	err = s.UpdateScheduler(WithUpdateLimitMode(2, LimitModeReschedule))
+	require.NoError(t, err)
+
+	limitMode := s.GetLimitMode()
+	require.NotNil(t, limitMode)
+
+	logger.Debug(fmt.Sprintf("Current limit mode: %v, limit: %d", limitMode.mode, limitMode.limit))
+
+	assert.Equal(t, LimitModeReschedule, int(limitMode.mode), "Limit mode should be LimitModeReschedule")
+	assert.Equal(t, uint(2), limitMode.limit, "Limit should be 2")
+
+	// Wait for a few more job runs to ensure the scheduler is still functioning
+	jobCount := 0
+	timeout := time.After(2 * time.Second)
+	for jobCount < 3 {
+		select {
+		case <-jobRan:
+			jobCount++
+			logger.Debug(fmt.Sprintf("Job completed, count: %d", jobCount))
+		case <-timeout:
+			t.Fatalf("Timed out waiting for jobs to run. Only %d jobs completed.", jobCount)
+		}
+	}
+
+	// Initiate shutdown
+	logger.Debug("Initiating scheduler shutdown")
+	shutdownErr := make(chan error, 1)
+	go func() {
+		shutdownErr <- s.Shutdown()
+	}()
+
+	// Allow time for in-progress jobs to complete
+	time.Sleep(300 * time.Millisecond)
+
+	// Check for any jobs that might have started just before shutdown
+	jobsAfterShutdownInitiated := 0
+	for {
+		select {
+		case <-jobStarted:
+			jobsAfterShutdownInitiated++
+			logger.Debug(fmt.Sprintf("Job started after shutdown initiated: %d", jobsAfterShutdownInitiated))
+		case <-jobRan:
+			logger.Debug("Job completed after shutdown initiated")
+		case err := <-shutdownErr:
+			require.NoError(t, err, "Shutdown should complete without error")
+			logger.Debug("Scheduler shutdown completed")
+			return
+		case <-time.After(500 * time.Millisecond):
+			t.Fatal("Timed out waiting for scheduler to shut down")
+		}
+	}
+}