add worker_limit option for server code generation (#3376)

* add property in exec

* add semaphore for goroutine limitation in template

* generation test with worker_limit option

* add comment

* update init-template

* misc

api/generate_test.go

@@ -34,6 +34,10 @@ func TestGenerate(t *testing.T) {
 			name:    "federation2",
 			workDir: filepath.Join(wd, "testdata", "federation2"),
 		},
+		{
+			name:    "worker_limit",
+			workDir: filepath.Join(wd, "testdata", "workerlimit"),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {

api/testdata/workerlimit/gqlgen.yml

@@ -0,0 +1,70 @@
+# Where are all the schema files located? globs are supported eg  src/**/*.graphqls
+schema:
+  - graph/*.graphqls
+
+# Where should the generated server code go?
+exec:
+  filename: graph/generated.go
+  package: graph
+  worker_limit: 1
+
+# Uncomment to enable federation
+# federation:
+#   filename: graph/federation.go
+#   package: graph
+
+# Where should any generated models go?
+model:
+  filename: graph/model/models_gen.go
+  package: model
+
+# Where should the resolver implementations go?
+resolver:
+  layout: follow-schema
+  dir: graph
+  package: graph
+
+# Optional: turn on use `gqlgen:"fieldName"` tags in your models
+# struct_tag: json
+
+# Optional: turn on to use []Thing instead of []*Thing
+# omit_slice_element_pointers: false
+
+# Optional: turn off to make struct-type struct fields not use pointers
+# e.g. type Thing struct { FieldA OtherThing } instead of { FieldA *OtherThing }
+# struct_fields_always_pointers: true
+
+# Optional: turn off to make resolvers return values instead of pointers for structs
+# resolvers_always_return_pointers: true
+
+# Optional: turn on to return pointers instead of values in unmarshalInput
+# return_pointers_in_unmarshalinput: false
+
+# Optional: wrap nullable input fields with Omittable
+# nullable_input_omittable: true
+
+# Optional: set to speed up generation time by not performing a final validation pass.
+# skip_validation: true
+
+# gqlgen will search for any type names in the schema in these go packages
+# if they match it will use them, otherwise it will generate them.
+autobind:
+  - "github.com/99designs/gqlgen/api/testdata/default/graph/model"
+
+# This section declares type mapping between the GraphQL and go type systems
+#
+# The first line in each type will be used as defaults for resolver arguments and
+# modelgen, the others will be allowed when binding to fields. Configure them to
+# your liking
+models:
+  ID:
+    model:
+      - github.com/99designs/gqlgen/graphql.ID
+      - github.com/99designs/gqlgen/graphql.Int
+      - github.com/99designs/gqlgen/graphql.Int64
+      - github.com/99designs/gqlgen/graphql.Int32
+  Int:
+    model:
+      - github.com/99designs/gqlgen/graphql.Int
+      - github.com/99designs/gqlgen/graphql.Int64
+      - github.com/99designs/gqlgen/graphql.Int32

api/testdata/workerlimit/graph/model/doc.go

@@ -0,0 +1 @@
+package model

api/testdata/workerlimit/graph/schema.graphqls

@@ -0,0 +1,28 @@
+# GraphQL schema example
+#
+# https://gqlgen.com/getting-started/
+
+type Todo {
+  id: ID!
+  text: String!
+  done: Boolean!
+  user: User!
+}
+
+type User {
+  id: ID!
+  name: String!
+}
+
+type Query {
+  todos: [Todo!]!
+}
+
+input NewTodo {
+  text: String!
+  userId: String!
+}
+
+type Mutation {
+  createTodo(input: NewTodo!): Todo!
+}

codegen/config/exec.go

@@ -20,6 +20,12 @@ type ExecConfig struct {
 	// Only for follow-schema layout:
 	FilenameTemplate string `yaml:"filename_template,omitempty"` // String template with {name} as placeholder for base name.
 	DirName          string `yaml:"dir"`
+
+	// Maximum number of goroutines in concurrency to use when running multiple child resolvers
+	// Suppressing the number of goroutines generated can reduce memory consumption per request,
+	// but processing time may increase due to the reduced number of concurrences
+	// Default: 0 (unlimited)
+	WorkerLimit uint `yaml:"worker_limit"`
 }
 
 type ExecLayout string

codegen/generated!.gotpl

@@ -10,6 +10,7 @@
 {{ reserveImport "bytes"  }}
 {{ reserveImport "embed"  }}
 
+{{ reserveImport "golang.org/x/sync/semaphore"}}
 {{ reserveImport "github.com/vektah/gqlparser/v2" "gqlparser" }}
 {{ reserveImport "github.com/vektah/gqlparser/v2/ast" }}
 {{ reserveImport "github.com/99designs/gqlgen/graphql" }}

codegen/type.gotpl

@@ -101,6 +101,9 @@
 				ret := make(graphql.Array, len(v))
 				{{- if not $type.IsScalar }}
 					var wg sync.WaitGroup
+					{{- if gt $.Config.Exec.WorkerLimit 0 }}
+						sm := semaphore.NewWeighted({{ $.Config.Exec.WorkerLimit }})
+					{{- end }}
 					isLen1 := len(v) == 1
 					if !isLen1 {
 						wg.Add(len(v))
@@ -124,14 +127,29 @@
 							}()
 							{{- end }}
 							if !isLen1 {
-								defer wg.Done()
+								{{- if gt $.Config.Exec.WorkerLimit 0 }}
+									defer func(){
+										sm.Release(1)
+										wg.Done()
+									}()
+								{{- else }}
+									defer wg.Done()
+								{{- end }}
 							}
 							ret[i] = ec.{{ $type.Elem.MarshalFunc }}(ctx, sel, v[i])
 						}
 						if isLen1 {
 							f(i)
 						} else {
-							go f(i)
+							{{- if gt $.Config.Exec.WorkerLimit 0 }}
+								if err := sm.Acquire(ctx, 1); err != nil {
+									ec.Error(ctx, ctx.Err())
+								} else {
+									go f(i)
+								}
+							{{- else }}
+								go f(i)
+							{{- end }}
 						}
 					{{ else }}
 						ret[i] = ec.{{ $type.Elem.MarshalFunc }}(ctx, sel, v[i])

init-templates/gqlgen.yml.gotmpl

@@ -6,6 +6,8 @@ schema:
 exec:
   filename: graph/generated.go
   package: graph
+  # Optional: Maximum number of goroutines in concurrency to use per child resolvers(default: unlimited)
+  # worker_limit: 1000
 
 # Uncomment to enable federation
 # federation: