test: add test for effect of UV_THREADPOOL_SIZE

This (not particularly elegant) native addon tests the effect of
UV_THREADPOOL_SIZE on node-api. The test fails if Node.js allows more
than UV_THREADPOOL_SIZE async tasks to run concurrently, or if it limits
the number of concurrent async tasks to anything less than
UV_THREADPOOL_SIZE.

test/node-api/test_uv_threadpool_size/binding.gyp

@@ -0,0 +1,8 @@
+{
+  "targets": [
+    {
+      "target_name": "test_uv_threadpool_size",
+      "sources": [ "test_uv_threadpool_size.c" ]
+    }
+  ]
+}

test/node-api/test_uv_threadpool_size/test.js

@@ -0,0 +1,7 @@
+'use strict';
+const common = require('../../common');
+const { test } = require(`./build/${common.buildType}/test_uv_threadpool_size`);
+
+const uvThreadpoolSize = parseInt(process.env.EXPECTED_UV_THREADPOOL_SIZE ||
+                                  process.env.UV_THREADPOOL_SIZE, 10) || 4;
+test(uvThreadpoolSize);

test/node-api/test_uv_threadpool_size/test_uv_threadpool_size.c

@@ -0,0 +1,178 @@
+#undef NDEBUG
+#include <assert.h>
+#include <node_api.h>
+#include <stdlib.h>
+#include <uv.h>
+#include "../../js-native-api/common.h"
+
+typedef struct {
+  uv_mutex_t mutex;
+  uint32_t threadpool_size;
+  uint32_t n_tasks_started;
+  uint32_t n_tasks_exited;
+  uint32_t n_tasks_finalized;
+  bool observed_saturation;
+} async_shared_data;
+
+typedef struct {
+  uint32_t task_id;
+  async_shared_data* shared_data;
+  napi_async_work request;
+} async_carrier;
+
+static inline bool all_tasks_started(async_shared_data* d) {
+  assert(d->n_tasks_started <= d->threadpool_size + 1);
+  return d->n_tasks_started == d->threadpool_size + 1;
+}
+
+static inline bool all_tasks_exited(async_shared_data* d) {
+  assert(d->n_tasks_exited <= d->n_tasks_started);
+  return all_tasks_started(d) && d->n_tasks_exited == d->n_tasks_started;
+}
+
+static inline bool all_tasks_finalized(async_shared_data* d) {
+  assert(d->n_tasks_finalized <= d->n_tasks_exited);
+  return all_tasks_exited(d) && d->n_tasks_finalized == d->n_tasks_exited;
+}
+
+static inline bool still_saturating(async_shared_data* d) {
+  return d->n_tasks_started < d->threadpool_size;
+}
+
+static inline bool threadpool_saturated(async_shared_data* d) {
+  return d->n_tasks_started == d->threadpool_size && d->n_tasks_exited == 0;
+}
+
+static inline bool threadpool_desaturating(async_shared_data* d) {
+  return d->n_tasks_started >= d->threadpool_size && d->n_tasks_exited != 0;
+}
+
+static inline void print_info(const char* label, async_carrier* c) {
+  async_shared_data* d = c->shared_data;
+  printf("%s task_id=%u n_tasks_started=%u n_tasks_exited=%u "
+         "n_tasks_finalized=%u observed_saturation=%d\n",
+         label, c->task_id, d->n_tasks_started, d->n_tasks_exited,
+         d->n_tasks_finalized, d->observed_saturation);
+}
+
+static void Execute(napi_env env, void* data) {
+  async_carrier* c = (async_carrier*) data;
+  async_shared_data* d = c->shared_data;
+
+  // As long as fewer than threadpool_size async tasks have been started, more
+  // should be started (eventually). Only once that happens should scheduled
+  // async tasks remain queued.
+  uv_mutex_lock(&d->mutex);
+  bool should_be_concurrent = still_saturating(d);
+  d->n_tasks_started++;
+  assert(d->n_tasks_started <= d->threadpool_size + 1);
+
+  print_info("start", c);
+
+  if (should_be_concurrent) {
+    // Wait for the thread pool to be saturated. This is not an elegant way of
+    // doing so, but it really does not matter much here.
+    while (still_saturating(d)) {
+      print_info("waiting", c);
+      uv_mutex_unlock(&d->mutex);
+      uv_sleep(100);
+      uv_mutex_lock(&d->mutex);
+    }
+
+    // One async task will observe that the threadpool is saturated, that is,
+    // that threadpool_size tasks have been started and none have exited yet.
+    // That task will be the first to exit.
+    if (!d->observed_saturation) {
+      assert(threadpool_saturated(d));
+      d->observed_saturation = true;
+    } else {
+      assert(threadpool_saturated(d) || threadpool_desaturating(d));
+    }
+  } else {
+    // If this task is not among the first threadpool_size tasks, it should not
+    // have been started unless other tasks have already finished.
+    assert(threadpool_desaturating(d));
+  }
+
+  print_info("exit", c);
+
+  // Allow other tasks to access the shared data. If the thread pool is actually
+  // larger than threadpool_size, this allows an extraneous task to start, which
+  // will lead to an assertion error.
+  uv_mutex_unlock(&d->mutex);
+  uv_sleep(1000);
+  uv_mutex_lock(&d->mutex);
+
+  d->n_tasks_exited++;
+  uv_mutex_unlock(&d->mutex);
+}
+
+static void Complete(napi_env env, napi_status status, void* data) {
+  async_carrier* c = (async_carrier*) data;
+  async_shared_data* d = c->shared_data;
+
+  if (status != napi_ok) {
+    napi_throw_type_error(env, NULL, "Execute callback failed.");
+    return;
+  }
+
+  uv_mutex_lock(&d->mutex);
+  assert(threadpool_desaturating(d));
+  d->n_tasks_finalized++;
+  print_info("finalize", c);
+  if (all_tasks_finalized(d)) {
+    uv_mutex_unlock(&d->mutex);
+    uv_mutex_destroy(&d->mutex);
+    free(d);
+  } else {
+    uv_mutex_unlock(&d->mutex);
+  }
+
+  NODE_API_CALL_RETURN_VOID(env, napi_delete_async_work(env, c->request));
+  free(c);
+}
+
+static napi_value Test(napi_env env, napi_callback_info info) {
+  size_t argc = 1;
+  napi_value argv[1];
+  napi_value this;
+  void* data;
+  NODE_API_CALL(env, napi_get_cb_info(env, info, &argc, argv, &this, &data));
+  NODE_API_ASSERT(env, argc >= 1, "Not enough arguments, expected 1.");
+
+  async_shared_data* shared_data = calloc(1, sizeof(async_shared_data));
+  assert(shared_data != NULL);
+  int ret = uv_mutex_init(&shared_data->mutex);
+  assert(ret == 0);
+
+  napi_valuetype t;
+  NODE_API_CALL(env, napi_typeof(env, argv[0], &t));
+  NODE_API_ASSERT(env, t == napi_number,
+      "Wrong first argument, integer expected.");
+  NODE_API_CALL(env,
+      napi_get_value_uint32(env, argv[0], &shared_data->threadpool_size));
+
+  napi_value resource_name;
+  NODE_API_CALL(env, napi_create_string_utf8(
+      env, "TestResource", NAPI_AUTO_LENGTH, &resource_name));
+
+  for (uint32_t i = 0; i <= shared_data->threadpool_size; i++) {
+    async_carrier* carrier = malloc(sizeof(async_carrier));
+    assert(carrier != NULL);
+    carrier->task_id = i;
+    carrier->shared_data = shared_data;
+    NODE_API_CALL(env, napi_create_async_work(env, NULL, resource_name,
+        Execute, Complete, carrier, &carrier->request));
+    NODE_API_CALL(env, napi_queue_async_work(env, carrier->request));
+  }
+
+  return NULL;
+}
+
+static napi_value Init(napi_env env, napi_value exports) {
+  napi_property_descriptor desc = DECLARE_NODE_API_PROPERTY("test", Test);
+  NODE_API_CALL(env, napi_define_properties(env, exports, 1, &desc));
+  return exports;
+}
+
+NAPI_MODULE(NODE_GYP_MODULE_NAME, Init)