MojoLPM: Remove re-entrancy and use of RunUntilIdle.

The existing example fuzzer code used RunUntilIdle to avoid runloop
recursion issues caused by re-entrancy in the scheduling of fuzzer
tasks. This change removes the re-entrancy and refactors out the use
of RunUntilIdle, working towards refactoring out the common code
duplication between fuzzers that's currently necessary.

Bug: 1076336
Change-Id: I3729d20264638c00c14c3a8149395e3f22e90089
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2329531
Commit-Queue: Mark Brand <markbrand@google.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799545}

content/test/data/fuzzer_corpus/code_cache_host_mojolpm_fuzzer/did_generate_cacheable_metadata_origin_a.textproto

@@ -6,7 +6,7 @@ actions {
   }
 }
 actions {
-  code_cache_host_call {
+  code_cache_host_remote_action {
     id: 1
     m_did_generate_cacheable_metadata {
       m_cache_type: CodeCacheType_kJavascript

content/test/data/fuzzer_corpus/code_cache_host_mojolpm_fuzzer/did_generate_cacheable_metadata_origin_b.textproto

@@ -6,7 +6,7 @@ actions {
   }
 }
 actions {
-  code_cache_host_call {
+  code_cache_host_remote_action {
     id: 1
     m_did_generate_cacheable_metadata {
       m_cache_type: CodeCacheType_kJavascript

content/test/fuzzer/code_cache_host_mojolpm_fuzzer.proto

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Message format for the MojoLPM fuzzer for the CodeCacheHost interface.
+
 syntax = "proto2";
 
 package content.fuzzing.code_cache_host.proto;
 
 import "third_party/blink/public/mojom/loader/code_cache.mojom.mojolpm.proto";
 
-message NewCodeCacheHost {
+// Bind a new CodeCacheHost remote
+message NewCodeCacheHostAction {
   enum OriginId {
     ORIGIN_A = 0;
     ORIGIN_B = 1;
@@ -17,7 +24,10 @@ message NewCodeCacheHost {
   required OriginId origin_id = 3;
 }
 
-message RunUntilIdle {
+// Run the specific sequence for (an indeterminate) period. This is not
+// intended to create a specific ordering, but to allow the fuzzer to delay a
+// later task until previous tasks have completed.
+message RunThreadAction {
   enum ThreadId {
     IO = 0;
     UI = 1;
@@ -26,18 +36,23 @@ message RunUntilIdle {
   required ThreadId id = 1;
 }
 
+// Actions that can be performed by the fuzzer.
 message Action {
   oneof action {
-    NewCodeCacheHost new_code_cache_host = 1;
-    RunUntilIdle run_until_idle = 2;
-    mojolpm.blink.mojom.CodeCacheHost.RemoteCall code_cache_host_call = 3;
+    NewCodeCacheHostAction new_code_cache_host = 1;
+    RunThreadAction run_thread = 2;
+    mojolpm.blink.mojom.CodeCacheHost.RemoteAction
+        code_cache_host_remote_action = 3;
   }
 }
 
+// Sequence provides a level of indirection which allows Testcase to compactly
+// express repeated sequences of actions.
 message Sequence {
   repeated uint32 action_indexes = 1 [packed = true];
 }
 
+// Testcase is the top-level message type interpreted by the fuzzer.
 message Testcase {
   repeated Action actions = 1;
   repeated Sequence sequences = 2;

mojo/public/tools/bindings/generators/mojolpm_templates/mojolpm.cc.tmpl

@@ -93,7 +93,6 @@ class {{interface.name}}Impl : public {{mojom_type}} {
 {%-       if method.response_parameters != None %}
     mojolpm::GetContext()->AddInstance<{{mojom_type}}::{{method.name}}Callback>(std::move(callback));
 {%-       endif %}
-    mojolpm::GetContext()->NextAction();
   }
 {%-   endfor %}
 };
@@ -251,16 +250,16 @@ bool ToProto(::mojo::PendingAssociatedReceiver<{{mojom_type}}>&& input,
 {%-   set mojom_type = interface|get_qualified_name_for_kind(flatten_nested_kind=True) %}
 {%-   set proto_type = "::mojolpm" ~ (interface|get_qualified_name_for_kind(flatten_nested_kind=True)) %}
 {%-   if interface.methods %}
-bool HandleRemoteCall(const {{proto_type}}::RemoteCall& input) {
+bool HandleRemoteAction(const {{proto_type}}::RemoteAction& input) {
   bool result = true;
 
   switch (input.method_case()) {
 {%-     for method in interface.methods %}
-    case {{proto_type}}::RemoteCall::k{{("m_" ~ method.name)|under_to_camel(digits_split=True)}}: {
+    case {{proto_type}}::RemoteAction::k{{("m_" ~ method.name)|under_to_camel(digits_split=True)}}: {
       result = HandleRemoteCall(input.id(), input.{{("m" ~ method.name)|camel_to_under}}());
     } break;
 {%-     endfor %}
-    case {{proto_type}}::RemoteCall::kReset: {
+    case {{proto_type}}::RemoteAction::kReset: {
       mojolpm::GetContext()->GetAndRemoveInstance<::mojo::Remote<{{mojom_type}}>>(input.id());
     } break;
 
@@ -272,16 +271,16 @@ bool HandleRemoteCall(const {{proto_type}}::RemoteCall& input) {
   return result;
 }
 
-bool HandleAssociatedRemoteCall(const {{proto_type}}::AssociatedRemoteCall& input) {
+bool HandleAssociatedRemoteAction(const {{proto_type}}::AssociatedRemoteAction& input) {
   bool result = true;
 
   switch (input.method_case()) {
 {%-     for method in interface.methods %}
-    case {{proto_type}}::AssociatedRemoteCall::k{{("m_" ~ method.name)|under_to_camel(digits_split=True)}}: {
+    case {{proto_type}}::AssociatedRemoteAction::k{{("m_" ~ method.name)|under_to_camel(digits_split=True)}}: {
       result = HandleAssociatedRemoteCall(input.id(), input.{{("m" ~ method.name)|camel_to_under}}());
     } break;
 {%-     endfor %}
-    case {{proto_type}}::AssociatedRemoteCall::kReset: {
+    case {{proto_type}}::AssociatedRemoteAction::kReset: {
       mojolpm::GetContext()->GetAndRemoveInstance<::mojo::AssociatedRemote<{{mojom_type}}>>(input.id());
     } break;
 
@@ -293,12 +292,12 @@ bool HandleAssociatedRemoteCall(const {{proto_type}}::AssociatedRemoteCall& inpu
   return result;
 }
 
-bool HandleResponse(
-    const {{proto_type}}::ReceiverResponse& input) {
+bool HandleReceiverAction(
+    const {{proto_type}}::ReceiverAction& input) {
   bool result = true;
   switch (input.response_case()) {
 {%-     for method in interface.methods %}
-    case {{proto_type}}::ReceiverResponse::k{{("m_" ~ method.name ~ "_response")|under_to_camel(digits_split=True)}}: {
+    case {{proto_type}}::ReceiverAction::k{{("m_" ~ method.name ~ "_response")|under_to_camel(digits_split=True)}}: {
       result = HandleResponse(input.id(), input.{{("m" ~ method.name ~ "_response")|camel_to_under}}());
     } break;
 {%-     endfor %}
@@ -326,7 +325,6 @@ static void {{interface.name}}_{{method.name}}Callback(
 {{ util.add_instance(kind, 'param_' ~ name, False) }}
 {%-         endfor %}
   mojolpmdbg("{{interface.name}}.{{method.name}}Callback\n");
-  mojolpm::GetContext()->NextAction();
 }{{"\n"-}}
 {%-       endif %}
 template <typename T>

mojo/public/tools/bindings/generators/mojolpm_templates/mojolpm.h.tmpl

@@ -177,14 +177,14 @@ bool ToProto(
 {%-   set mojom_type = interface|get_qualified_name_for_kind(flatten_nested_kind=True) %}
 {%-   set proto_type = "::mojolpm" ~ (interface|get_qualified_name_for_kind(flatten_nested_kind=True)) %}
 {%-   if interface.methods %}
-bool HandleRemoteCall(
-  const {{proto_type}}::RemoteCall& input);
+bool HandleRemoteAction(
+  const {{proto_type}}::RemoteAction& input);
 
-bool HandleAssociatedRemoteCall(
-  const {{proto_type}}::AssociatedRemoteCall& input);
+bool HandleAssociatedRemoteAction(
+  const {{proto_type}}::AssociatedRemoteAction& input);
 
-bool HandleResponse(
-  const {{proto_type}}::ReceiverResponse& response);{{"\n"-}}
+bool HandleReceiverAction(
+  const {{proto_type}}::ReceiverAction& input);{{"\n"-}}
 {%-     for method in interface.methods %}
 bool HandleRemoteCall(
   uint32_t instance_id,

mojo/public/tools/bindings/generators/mojolpm_templates/mojolpm.proto.tmpl

@@ -316,7 +316,7 @@ message {{interface.name}} {
 {%-   endfor%}
 
 {%-   if interface.methods|length %}
-  message RemoteCall {
+  message RemoteAction {
     required uint32 id = 1;
 
     oneof method {
@@ -327,7 +327,7 @@ message {{interface.name}} {
     }
   }
 
-  message AssociatedRemoteCall {
+  message AssociatedRemoteAction {
     required uint32 id = 1;
 
     oneof method {
@@ -338,7 +338,7 @@ message {{interface.name}} {
     }
   }
 
-  message ReceiverResponse {
+  message ReceiverAction {
     required uint32 id = 1;
 
     oneof response {