feat: add job concurrency and basic support for needs job prop

WORKFLOW_SUPPORT.md

@@ -14,7 +14,7 @@ syntax](https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for
 - [x] jobs
   - [ ] jobs.<job_id>.name
   - [ ] jobs.<job_id>.permissions
-  - [ ] jobs.<job_id>.needs
+  - [x] jobs.<job_id>.needs (ordering, not success)
   - [ ] jobs.<job_id>.if
   - [x] jobs.<job_id>.runs-on
   - [ ] jobs.<job_id>.environment
@@ -46,7 +46,7 @@ syntax](https://docs.github.com/en/actions/writing-workflows/workflow-syntax-for
 
 ## Behaviours
 
-- [ ] Job concurrency
+- [x] Job concurrency
 - [ ] Logging to files
 - [ ] Support Actions
 - [ ] Support built-in functions

internal/runner/runner.go

@@ -5,6 +5,7 @@ import (
 	workflow "courgette/internal/workflow"
 	"errors"
 	"fmt"
+	"sync"
 )
 
 type Runner struct {
@@ -61,27 +62,39 @@ func (r *Runner) RunWorkflow(workflow workflow.Workflow) Task {
 	logger.Info("Executing workflow: %s", workflow.SourcePath)
 	task := r.GetTask(r.AddTask())
 
-	for _, job := range workflow.Jobs {
-		jobContext := task.GetJobContext(task.AddJob())
-		jobContext.SetStatus("started")
+	for _, group := range workflow.GetJobsAsGroups() {
+		var groupWait sync.WaitGroup
 
-		runnerImage := r.GetImageUriByLabel(job.RunsOn)
-		containerName := r.GetContainerName(jobContext.Id)
+		for _, job := range group {
+			groupWait.Add(1)
 
-		logger.Info("Using image %s (label: %s)", runnerImage, job.RunsOn)
+			go func() {
+				defer groupWait.Done()
+				jobContext := task.GetJobContext(task.AddJob())
 
-		if pullError := r.Driver.Pull(runnerImage); pullError != nil {
-			jobContext.SetStatus("failed").SetError(pullError)
-			continue
+				jobContext.SetStatus("started")
+
+				runnerImage := r.GetImageUriByLabel(job.RunsOn)
+				containerName := r.GetContainerName(jobContext.Id)
+
+				logger.Info("Using image %s (label: %s)", runnerImage, job.RunsOn)
+
+				if pullError := r.Driver.Pull(runnerImage); pullError != nil {
+					jobContext.SetStatus("failed").SetError(pullError)
+					return
+				}
+
+				if runError := r.RunJobInContainer(runnerImage, containerName, job); runError != nil {
+					jobContext.SetStatus("failed").SetError(runError)
+					return
+				}
+
+				jobContext.SetStatus("success")
+				r.deferred.RunDeferredTasksInScope(fmt.Sprintf("job-%s", containerName))
+			}()
 		}
 
-		if runError := r.RunJobInContainer(runnerImage, containerName, job); runError != nil {
-			jobContext.SetStatus("failed").SetError(runError)
-			continue
-		}
-
-		jobContext.SetStatus("success")
-		r.deferred.RunDeferredTasksInScope("job")
+		groupWait.Wait()
 	}
 
 	r.deferred.RunAllDeferredTasks()
@@ -113,7 +126,7 @@ func (r *Runner) RunCommandInContainer(containerId string, command string) error
 func (r *Runner) RunJobInContainer(imageUri string, containerId string, job workflow.Job) error {
 	r.Driver.Start(imageUri, containerId)
 
-	r.deferred.Queue("job", func() {
+	r.deferred.Queue(fmt.Sprintf("job-%s", containerId), func() {
 		logger.Info("Started cleaning up %s", containerId)
 		r.Driver.Stop(containerId)
 	})

internal/workflow/dependencies.go

@@ -0,0 +1,51 @@
+package workflow
+
+// Splits a flat map representing a graph's parent > children relationships
+// into an ordered slice of levels.
+func SplitFlatTreeIntoGroups(flatTree map[string][]string) [][]string {
+	type TreeNode struct {
+		name  string
+		level int
+	}
+
+	nodes := map[string]TreeNode{}
+
+	deepestLevel := 0
+	next := []string{""}
+
+	for len(next) > 0 {
+		current := next[0]
+		next = next[1:]
+		children := flatTree[current]
+
+		currentNode, found := nodes[current]
+
+		// The negative value represents the graph root.
+		currentLevel := -1
+
+		if found {
+			currentLevel = currentNode.level
+		}
+
+		for _, child := range children {
+			nodes[child] = TreeNode{
+				name:  child,
+				level: currentLevel + 1,
+			}
+		}
+
+		if deepestLevel < currentLevel {
+			deepestLevel = currentLevel
+		}
+
+		next = append(next, children...)
+	}
+
+	levels := make([][]string, deepestLevel+1)
+
+	for _, node := range nodes {
+		levels[node.level] = append(levels[node.level], node.name)
+	}
+
+	return levels
+}

internal/workflow/dependencies_test.go

@@ -0,0 +1,48 @@
+package workflow
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestSplitFlatTreeIntoGroupsProducesListOfLevels(t *testing.T) {
+	flatTree := map[string][]string{
+		"":  []string{"a"},
+		"a": []string{"b"},
+		"b": []string{"c"},
+		"c": []string{},
+	}
+
+	levels := SplitFlatTreeIntoGroups(flatTree)
+
+	expectedLevels := [][]string{
+		[]string{"a"},
+		[]string{"b"},
+		[]string{"c"},
+	}
+
+	if !reflect.DeepEqual(levels, expectedLevels) {
+		t.Errorf("Expected levels to be %+v, got %+v instead.", expectedLevels, levels)
+	}
+}
+
+func TestSplitFlatTreeIntoGroupsProducesListOfLevelsIfMultiparent(t *testing.T) {
+	flatTree := map[string][]string{
+		"":  []string{"a"},
+		"a": []string{"b", "c"},
+		"b": []string{"c"},
+		"c": []string{},
+	}
+
+	levels := SplitFlatTreeIntoGroups(flatTree)
+
+	expectedLevels := [][]string{
+		[]string{"a"},
+		[]string{"b"},
+		[]string{"c"},
+	}
+
+	if !reflect.DeepEqual(levels, expectedLevels) {
+		t.Errorf("Expected levels to be %+v, got %+v instead.", expectedLevels, levels)
+	}
+}

internal/workflow/models.go

@@ -5,8 +5,9 @@ import (
 )
 
 type Job struct {
-	RunsOn string `yaml:"runs-on"`
-	Steps  []Step `yaml:"steps"`
+	RunsOn string   `yaml:"runs-on"`
+	Steps  []Step   `yaml:"steps"`
+	Needs  []string `yaml:"needs"`
 }
 
 func (j Job) Validate() []error {
@@ -59,3 +60,35 @@ func (w Workflow) Validate() []error {
 
 	return validationErrors
 }
+
+// Creates a deterministic, ordered collection of jobs that respects
+// the jobs's dependencies.
+func (w Workflow) GetJobsAsGroups() [][]Job {
+	dependenciesMap := map[string][]string{}
+
+	for jobLabel, job := range w.Jobs {
+		if len(job.Needs) == 0 {
+			dependenciesMap[""] = append(dependenciesMap[""], jobLabel)
+		}
+
+		for _, need := range job.Needs {
+			dependenciesMap[need] = append(dependenciesMap[need], jobLabel)
+		}
+	}
+
+	levels := SplitFlatTreeIntoGroups(dependenciesMap)
+
+	groups := [][]Job{}
+
+	for _, jobLabels := range levels {
+		jobs := []Job{}
+
+		for _, jobLabel := range jobLabels {
+			jobs = append(jobs, w.Jobs[jobLabel])
+		}
+
+		groups = append(groups, jobs)
+	}
+
+	return groups
+}