fix: Max parallel Support for Matrix Jobs and Remote Action Tests (#150)

## Summary

This PR fixes the `max-parallel` strategy configuration for matrix jobs and resolves all failing tests in `step_action_remote_test.go`. The implementation ensures that matrix jobs respect the `max-parallel` setting, preventing resource exhaustion when running GitHub Actions workflows.

## Problem Statement

### Issue 1: max-parallel Not Working Correctly
Matrix jobs were running in parallel regardless of the `max-parallel` setting in the strategy configuration. This caused:
- Resource contention on limited runners
- Unpredictable job execution behavior
- Inability to control concurrency for resource-intensive workflows

### Issue 2: Failing Remote Action Tests
All tests in `step_action_remote_test.go` were failing due to:
- Missing `ActionCacheDir` configuration
- Incorrect mock expectations using fixed strings instead of hash-based paths
- Incompatibility with the hash-based action cache implementation

## Changes

### 1. max-parallel Implementation (`pkg/runner/runner.go`)

#### Robust Initialization
Added fallback logic to ensure `MaxParallel` is always properly initialized:
```go
if job.Strategy.MaxParallel == 0 {
    job.Strategy.MaxParallel = job.Strategy.GetMaxParallel()
}
```

#### Eliminated Unnecessary Nesting
Fixed inefficient nested parallelization when only one pipeline element exists:
```go
if len(pipeline) == 1 {
    // Execute directly without additional wrapper
    log.Debugf("Single pipeline element, executing directly")
    return pipeline[0](ctx)
}
```

#### Enhanced Logging
Added comprehensive debug and info logging:
- Shows which `maxParallel` value is being used
- Logs adjustments based on matrix size
- Reports final parallelization decisions

### 2. Worker Logging (`pkg/common/executor.go`)

Enhanced `NewParallelExecutor` with detailed worker activity logging:
```go
log.Infof("NewParallelExecutor: Creating %d workers for %d executors", parallel, len(executors))

for i := 0; i < parallel; i++ {
    go func(workerID int, work <-chan Executor, errs chan<- error) {
        log.Debugf("Worker %d started", workerID)
        taskCount := 0
        for executor := range work {
            taskCount++
            log.Debugf("Worker %d executing task %d", workerID, taskCount)
            errs <- executor(ctx)
        }
        log.Debugf("Worker %d finished (%d tasks executed)", workerID, taskCount)
    }(i, work, errs)
}
```

**Benefits:**
- Easy verification of correct parallelization
- Better debugging capabilities
- Clear visibility into worker activity

### 3. Documentation (`pkg/model/workflow.go`)

Added clarifying comment to ensure strategy values are always set:
```go
// Always set these values, even if there's an error later
j.Strategy.FailFast = j.Strategy.GetFailFast()
j.Strategy.MaxParallel = j.Strategy.GetMaxParallel()
```

### 4. Test Fixes (`pkg/runner/step_action_remote_test.go`)

#### Added Missing Configuration
All tests now include `ActionCacheDir`:
```go
Config: &Config{
    GitHubInstance: "github.com",
    ActionCacheDir: "/tmp/test-cache",
}
```

#### Hash-Based Suffix Matchers
Updated mocks to use hash-based paths instead of fixed strings:
```go
// Before
sarm.On("readAction", sar.Step, suffixMatcher("org-repo-path@ref"), ...)

// After
sarm.On("readAction", sar.Step, suffixMatcher(sar.Step.UsesHash()), ...)
```

#### Flexible Exec Matcher for Post Tests
Implemented flexible path matching for hash-based action directories:
```go
execMatcher := mock.MatchedBy(func(args []string) bool {
    if len(args) != 2 {
        return false
    }
    return args[0] == "node" && strings.Contains(args[1], "post.js")
})
```

#### Token Test Improvements
- Uses unique cache directory to force cloning
- Validates URL redirection to github.com
- Accepts realistic token behavior

### 5. New Tests

#### Unit Tests (`pkg/runner/max_parallel_test.go`)
Tests various `max-parallel` configurations:
- `max-parallel: 1` → Sequential execution
- `max-parallel: 2` → Max 2 parallel jobs
- `max-parallel: 4` (default) → Max 4 parallel jobs
- `max-parallel: 10` → Max 10 parallel jobs

#### Concurrency Test (`pkg/common/executor_max_parallel_test.go`)
Verifies that `max-parallel: 2` actually limits concurrent execution using atomic counters.

## Expected Behavior

### Before
- ❌ Jobs ran in parallel regardless of `max-parallel` setting
- ❌ Unnecessary nested parallelization (8 workers for 1 element)
- ❌ No logging to debug parallelization issues
- ❌ All `step_action_remote_test.go` tests failing

### After
- ✅ `max-parallel: 1` → Jobs run strictly sequentially
- ✅ `max-parallel: N` → Maximum N jobs run simultaneously
- ✅ Efficient single-level parallelization for matrix jobs
- ✅ Comprehensive logging for debugging
- ✅ All tests passing (10/10)

## Example Log Output

With `max-parallel: 2` and 6 matrix jobs:
```
[DEBUG] Using job.Strategy.MaxParallel: 2
[INFO] Running job with maxParallel=2 for 6 matrix combinations
[DEBUG] Single pipeline element, executing directly
[INFO] NewParallelExecutor: Creating 2 workers for 6 executors
[DEBUG] Worker 0 started
[DEBUG] Worker 1 started
[DEBUG] Worker 0 executing task 1
[DEBUG] Worker 1 executing task 1
...
[DEBUG] Worker 0 finished (3 tasks executed)
[DEBUG] Worker 1 finished (3 tasks executed)
```

## Test Results

All tests pass successfully:
```
✅ TestStepActionRemote (3 sub-tests)
✅ TestStepActionRemotePre
✅ TestStepActionRemotePreThroughAction
✅ TestStepActionRemotePreThroughActionToken
✅ TestStepActionRemotePost (4 sub-tests)
✅ TestMaxParallelStrategy
✅ TestMaxParallel2Quick

Total: 12/12 tests passing
```

## Breaking Changes

None. This PR is fully backward compatible. All changes improve existing behavior without altering the API.

## Impact

- ✅ Fixes resource management for CI/CD pipelines
- ✅ Prevents runner exhaustion on limited infrastructure
- ✅ Enables sequential execution for resource-intensive jobs
- ✅ Improves debugging with detailed logging
- ✅ Ensures test suite reliability

## Files Modified

### Core Implementation
- `pkg/runner/runner.go` - max-parallel fix + logging
- `pkg/common/executor.go` - Worker logging
- `pkg/model/workflow.go` - Documentation

### Tests
- `pkg/runner/step_action_remote_test.go` - Fixed all 10 tests
- `pkg/runner/max_parallel_test.go` - **NEW** - Unit tests
- `pkg/common/executor_max_parallel_test.go` - **NEW** - Concurrency test

## Verification

### Manual Testing
```bash
# Build
go build -o dist/act main.go

# Test with max-parallel: 2
./dist/act -W test-max-parallel-2.yml -v

# Expected: Only 2 jobs run simultaneously
```

### Automated Testing
```bash
# Run all tests
go test ./pkg/runner -run TestStepActionRemote -v
go test ./pkg/runner -run TestMaxParallel -v
go test ./pkg/common -run TestMaxParallel -v
```

## Related Issues

Fixes issues where matrix jobs in Gitea ignored the `max-parallel` strategy setting, causing resource contention and unpredictable behavior.

Reviewed-on: https://gitea.com/gitea/act/pulls/150
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: silverwind <silverwind@noreply.gitea.com>
Co-authored-by: Pascal Zimmermann <pascal.zimmermann@theiotstudio.com>
Co-committed-by: Pascal Zimmermann <pascal.zimmermann@theiotstudio.com>

pkg/common/executor.go

@@ -101,12 +101,19 @@ func NewParallelExecutor(parallel int, executors ...Executor) Executor {
 			parallel = 1
 		}
 
+		log.Infof("NewParallelExecutor: Creating %d workers for %d executors", parallel, len(executors))
+
 		for i := 0; i < parallel; i++ {
-			go func(work <-chan Executor, errs chan<- error) {
+			go func(workerID int, work <-chan Executor, errs chan<- error) {
+				log.Debugf("Worker %d started", workerID)
+				taskCount := 0
 				for executor := range work {
+					taskCount++
+					log.Debugf("Worker %d executing task %d", workerID, taskCount)
 					errs <- executor(ctx)
 				}
-			}(work, errs)
+				log.Debugf("Worker %d finished (%d tasks executed)", workerID, taskCount)
+			}(i, work, errs)
 		}
 
 		for i := 0; i < len(executors); i++ {

pkg/common/executor_max_parallel_test.go

@@ -0,0 +1,86 @@
+package common
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// Simple fast test that verifies max-parallel: 2 limits concurrency
+func TestMaxParallel2Quick(t *testing.T) {
+	ctx := context.Background()
+
+	var currentRunning int32
+	var maxSimultaneous int32
+
+	executors := make([]Executor, 4)
+	for i := 0; i < 4; i++ {
+		executors[i] = func(ctx context.Context) error {
+			current := atomic.AddInt32(&currentRunning, 1)
+
+			// Update max if needed
+			for {
+				maxValue := atomic.LoadInt32(&maxSimultaneous)
+				if current <= maxValue || atomic.CompareAndSwapInt32(&maxSimultaneous, maxValue, current) {
+					break
+				}
+			}
+
+			time.Sleep(10 * time.Millisecond)
+			atomic.AddInt32(&currentRunning, -1)
+			return nil
+		}
+	}
+
+	err := NewParallelExecutor(2, executors...)(ctx)
+
+	assert.NoError(t, err)
+	assert.LessOrEqual(t, atomic.LoadInt32(&maxSimultaneous), int32(2),
+		"Should not exceed max-parallel: 2")
+}
+
+// Test that verifies max-parallel: 1 enforces sequential execution
+func TestMaxParallel1Sequential(t *testing.T) {
+	ctx := context.Background()
+
+	var currentRunning int32
+	var maxSimultaneous int32
+	var executionOrder []int
+	var orderMutex sync.Mutex
+
+	executors := make([]Executor, 5)
+	for i := 0; i < 5; i++ {
+		taskID := i
+		executors[i] = func(ctx context.Context) error {
+			current := atomic.AddInt32(&currentRunning, 1)
+
+			// Track execution order
+			orderMutex.Lock()
+			executionOrder = append(executionOrder, taskID)
+			orderMutex.Unlock()
+
+			// Update max if needed
+			for {
+				maxValue := atomic.LoadInt32(&maxSimultaneous)
+				if current <= maxValue || atomic.CompareAndSwapInt32(&maxSimultaneous, maxValue, current) {
+					break
+				}
+			}
+
+			time.Sleep(20 * time.Millisecond)
+			atomic.AddInt32(&currentRunning, -1)
+			return nil
+		}
+	}
+
+	err := NewParallelExecutor(1, executors...)(ctx)
+
+	assert.NoError(t, err)
+	assert.Equal(t, int32(1), atomic.LoadInt32(&maxSimultaneous),
+		"max-parallel: 1 should only run 1 task at a time")
+	assert.Len(t, executionOrder, 5, "All 5 tasks should have executed")
+}

pkg/common/executor_parallel_advanced_test.go

@@ -0,0 +1,280 @@
+package common
+
+import (
+	"context"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestMaxParallelJobExecution tests actual job execution with max-parallel
+func TestMaxParallelJobExecution(t *testing.T) {
+	t.Run("MaxParallel=1 Sequential", func(t *testing.T) {
+		var currentRunning int32
+		var maxConcurrent int32
+		var executionOrder []int
+		var mu sync.Mutex
+
+		executors := make([]Executor, 5)
+		for i := 0; i < 5; i++ {
+			taskID := i
+			executors[i] = func(ctx context.Context) error {
+				current := atomic.AddInt32(&currentRunning, 1)
+
+				// Track max concurrent
+				for {
+					max := atomic.LoadInt32(&maxConcurrent)
+					if current <= max || atomic.CompareAndSwapInt32(&maxConcurrent, max, current) {
+						break
+					}
+				}
+
+				mu.Lock()
+				executionOrder = append(executionOrder, taskID)
+				mu.Unlock()
+
+				time.Sleep(10 * time.Millisecond)
+				atomic.AddInt32(&currentRunning, -1)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		err := NewParallelExecutor(1, executors...)(ctx)
+		assert.NoError(t, err)
+
+		assert.Equal(t, int32(1), maxConcurrent, "Should never exceed 1 concurrent execution")
+		assert.Len(t, executionOrder, 5, "All tasks should execute")
+	})
+
+	t.Run("MaxParallel=3 Limited", func(t *testing.T) {
+		var currentRunning int32
+		var maxConcurrent int32
+
+		executors := make([]Executor, 10)
+		for i := 0; i < 10; i++ {
+			executors[i] = func(ctx context.Context) error {
+				current := atomic.AddInt32(&currentRunning, 1)
+
+				for {
+					max := atomic.LoadInt32(&maxConcurrent)
+					if current <= max || atomic.CompareAndSwapInt32(&maxConcurrent, max, current) {
+						break
+					}
+				}
+
+				time.Sleep(20 * time.Millisecond)
+				atomic.AddInt32(&currentRunning, -1)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		err := NewParallelExecutor(3, executors...)(ctx)
+		assert.NoError(t, err)
+
+		assert.LessOrEqual(t, int(maxConcurrent), 3, "Should never exceed 3 concurrent executions")
+		assert.GreaterOrEqual(t, int(maxConcurrent), 1, "Should have at least 1 concurrent execution")
+	})
+
+	t.Run("MaxParallel=0 Uses1Worker", func(t *testing.T) {
+		var maxConcurrent int32
+		var currentRunning int32
+
+		executors := make([]Executor, 5)
+		for i := 0; i < 5; i++ {
+			executors[i] = func(ctx context.Context) error {
+				current := atomic.AddInt32(&currentRunning, 1)
+
+				for {
+					max := atomic.LoadInt32(&maxConcurrent)
+					if current <= max || atomic.CompareAndSwapInt32(&maxConcurrent, max, current) {
+						break
+					}
+				}
+
+				time.Sleep(10 * time.Millisecond)
+				atomic.AddInt32(&currentRunning, -1)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		// When maxParallel is 0 or negative, it defaults to 1
+		err := NewParallelExecutor(0, executors...)(ctx)
+		assert.NoError(t, err)
+
+		assert.Equal(t, int32(1), maxConcurrent, "Should use 1 worker when max-parallel is 0")
+	})
+}
+
+// TestMaxParallelWithErrors tests error handling with max-parallel
+func TestMaxParallelWithErrors(t *testing.T) {
+	t.Run("OneTaskFailsOthersContinue", func(t *testing.T) {
+		var successCount int32
+
+		executors := make([]Executor, 5)
+		for i := 0; i < 5; i++ {
+			taskID := i
+			executors[i] = func(ctx context.Context) error {
+				if taskID == 2 {
+					return assert.AnError
+				}
+				atomic.AddInt32(&successCount, 1)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		err := NewParallelExecutor(2, executors...)(ctx)
+
+		// Should return the error from task 2
+		assert.Error(t, err)
+
+		// Other tasks should still execute
+		assert.Equal(t, int32(4), successCount, "4 tasks should succeed")
+	})
+
+	t.Run("ContextCancellation", func(t *testing.T) {
+		ctx, cancel := context.WithCancel(context.Background())
+
+		var startedCount int32
+		executors := make([]Executor, 10)
+		for i := 0; i < 10; i++ {
+			executors[i] = func(ctx context.Context) error {
+				atomic.AddInt32(&startedCount, 1)
+				time.Sleep(100 * time.Millisecond)
+				return nil
+			}
+		}
+
+		// Cancel after a short delay
+		go func() {
+			time.Sleep(30 * time.Millisecond)
+			cancel()
+		}()
+
+		err := NewParallelExecutor(3, executors...)(ctx)
+		assert.Error(t, err)
+		assert.ErrorIs(t, err, context.Canceled)
+
+		// Not all tasks should start due to cancellation (but timing may vary)
+		// Just verify cancellation occurred
+		t.Logf("Started %d tasks before cancellation", startedCount)
+	})
+}
+
+// TestMaxParallelPerformance tests performance characteristics
+func TestMaxParallelPerformance(t *testing.T) {
+	if testing.Short() {
+		t.Skip("Skipping performance test in short mode")
+	}
+
+	t.Run("ParallelFasterThanSequential", func(t *testing.T) {
+		executors := make([]Executor, 10)
+		for i := 0; i < 10; i++ {
+			executors[i] = func(ctx context.Context) error {
+				time.Sleep(50 * time.Millisecond)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+
+		// Sequential (max-parallel=1)
+		start := time.Now()
+		err := NewParallelExecutor(1, executors...)(ctx)
+		sequentialDuration := time.Since(start)
+		assert.NoError(t, err)
+
+		// Parallel (max-parallel=5)
+		start = time.Now()
+		err = NewParallelExecutor(5, executors...)(ctx)
+		parallelDuration := time.Since(start)
+		assert.NoError(t, err)
+
+		// Parallel should be significantly faster
+		assert.Less(t, parallelDuration, sequentialDuration/2,
+			"Parallel execution should be at least 2x faster")
+	})
+
+	t.Run("OptimalWorkerCount", func(t *testing.T) {
+		executors := make([]Executor, 20)
+		for i := 0; i < 20; i++ {
+			executors[i] = func(ctx context.Context) error {
+				time.Sleep(10 * time.Millisecond)
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+
+		// Test with different worker counts
+		workerCounts := []int{1, 2, 5, 10, 20}
+		durations := make(map[int]time.Duration)
+
+		for _, count := range workerCounts {
+			start := time.Now()
+			err := NewParallelExecutor(count, executors...)(ctx)
+			durations[count] = time.Since(start)
+			assert.NoError(t, err)
+		}
+
+		// More workers should generally be faster (up to a point)
+		assert.Less(t, durations[5], durations[1], "5 workers should be faster than 1")
+		assert.Less(t, durations[10], durations[2], "10 workers should be faster than 2")
+	})
+}
+
+// TestMaxParallelResourceSharing tests resource sharing scenarios
+func TestMaxParallelResourceSharing(t *testing.T) {
+	t.Run("SharedResourceWithMutex", func(t *testing.T) {
+		var sharedCounter int
+		var mu sync.Mutex
+
+		executors := make([]Executor, 100)
+		for i := 0; i < 100; i++ {
+			executors[i] = func(ctx context.Context) error {
+				mu.Lock()
+				sharedCounter++
+				mu.Unlock()
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		err := NewParallelExecutor(10, executors...)(ctx)
+		assert.NoError(t, err)
+
+		assert.Equal(t, 100, sharedCounter, "All tasks should increment counter")
+	})
+
+	t.Run("ChannelCommunication", func(t *testing.T) {
+		resultChan := make(chan int, 50)
+
+		executors := make([]Executor, 50)
+		for i := 0; i < 50; i++ {
+			taskID := i
+			executors[i] = func(ctx context.Context) error {
+				resultChan <- taskID
+				return nil
+			}
+		}
+
+		ctx := context.Background()
+		err := NewParallelExecutor(5, executors...)(ctx)
+		assert.NoError(t, err)
+
+		close(resultChan)
+
+		results := make(map[int]bool)
+		for result := range resultChan {
+			results[result] = true
+		}
+
+		assert.Len(t, results, 50, "All task IDs should be received")
+	})
+}