src: make ProcessMetrics API thread-safe

Previous calls to Update() or Get() could cause corruption because they
could attempt to write to stor_ from different threads. Put a lock
around all access to stor_ so that doesn't happen.

PR-URL: #86
Reviewed-by: Santiago Gimeno <santiago.gimeno@gmail.com>

src/nsolid.cc

@@ -151,12 +151,19 @@ static int get_cpu_usage(uint64_t* fields, uv_rusage_t* ru = nullptr) {
 ProcessMetrics::ProcessMetrics() : cpu_prev_time_(uv_hrtime()) {
   int er = get_cpu_usage(cpu_prev_);
   CHECK_EQ(er, 0);
+  CHECK_EQ(uv_mutex_init(&stor_lock_), 0);
+}
+
+
+ProcessMetrics::~ProcessMetrics() {
+  uv_mutex_destroy(&stor_lock_);
 }
 
 
 std::string ProcessMetrics::toJSON() {
   std::string metrics_string;
 
+  uv_mutex_lock(&stor_lock_);
   metrics_string += "{";
 #define V(Type, CName, JSName, MType)                                          \
   metrics_string += "\"" #JSName "\":";                                        \
@@ -173,13 +180,17 @@ std::string ProcessMetrics::toJSON() {
   metrics_string += "\"cpu\":";
   metrics_string += std::to_string(stor_.cpu_percent);
   metrics_string += "}";
+  uv_mutex_unlock(&stor_lock_);
 
   return metrics_string;
 }
 
 
 ProcessMetrics::MetricsStor ProcessMetrics::Get() {
-  return stor_;
+  uv_mutex_lock(&stor_lock_);
+  auto stor = stor_;
+  uv_mutex_unlock(&stor_lock_);
+  return stor;
 }
 
 
@@ -223,6 +234,7 @@ int ProcessMetrics::Update() {
   cpu_percent[1] = (cpu[1] - cpu_prev_[1]) * 100.0 * 1000.0 / elapsed;
   cpu_percent[2] = (cpu[2] - cpu_prev_[2]) * 100.0 * 1000.0 / elapsed;
 
+  uv_mutex_lock(&stor_lock_);
   stor_.title = title_buf;
   stor_.user = pwd.username;
   stor_.timestamp = duration_cast<milliseconds>(
@@ -249,6 +261,7 @@ int ProcessMetrics::Update() {
   stor_.cpu_system_percent = cpu_percent[1];
   stor_.cpu_percent = cpu_percent[2];
   stor_.cpu = stor_.cpu_percent;
+  uv_mutex_unlock(&stor_lock_);
 
   cpu_prev_[0] = cpu[0];
   cpu_prev_[1] = cpu[1];

src/nsolid.h

@@ -561,7 +561,7 @@ class NODE_EXTERN ProcessMetrics {
    * @brief Destroy the Process Metrics object
    *
    */
-  ~ProcessMetrics() = default;
+  ~ProcessMetrics();
 
   /**
    * @brief struct to store process metrics data.
@@ -598,6 +598,7 @@ class NODE_EXTERN ProcessMetrics {
   int Update();
 
  private:
+  uv_mutex_t stor_lock_;
   MetricsStor stor_;
   uint64_t cpu_prev_[3];
   uint64_t cpu_prev_time_;

test/addons/nsolid-proc-metrics/binding.cc

@@ -5,11 +5,10 @@
 #include <assert.h>
 
 node::nsolid::ProcessMetrics proc_metrics_;
-node::nsolid::ProcessMetrics::MetricsStor proc_stor;
 
 static void GetMetrics(const v8::FunctionCallbackInfo<v8::Value>& args) {
   assert(0 == proc_metrics_.Update());
-  proc_stor = proc_metrics_.Get();
+  node::nsolid::ProcessMetrics::MetricsStor proc_stor = proc_metrics_.Get();
   assert(proc_stor.system_uptime > 0);
 }