be less crazy with getrusage

service/endpoint.cc

@@ -660,16 +660,24 @@ void
 EndpointBase::
 doMinLatencyPolling(int threadNum, int numThreads)
 {
+    int epoch = 0;
+
     while (!shutdown_) {
-        // query the kernel for performance metrics
-        rusage now;
-        getrusage(RUSAGE_THREAD, &now);
-
-        // if we're just started, assume we know nothing and don't update the usage
-        long s = now.ru_utime.tv_sec+now.ru_stime.tv_sec;
-        if(s > 1) {
-            std::lock_guard<std::mutex> guard(usageLock);
-            resourceUsage[threadNum] = now;
+        // sync with the loop monitor request
+        int i = resourceEpoch;
+        if(i != epoch) {
+            // query the kernel for performance metrics
+            rusage now;
+            getrusage(RUSAGE_THREAD, &now);
+
+            // if we're just started, assume we know nothing and don't update the usage
+            long s = now.ru_utime.tv_sec+now.ru_stime.tv_sec;
+            if(s > 1) {
+                std::lock_guard<std::mutex> guard(usageLock);
+                resourceUsage[threadNum] = now;
+            }
+
+            epoch = i;
         }
 
         handleEvents(0, 1, handleEvent);

service/endpoint.h

@@ -23,6 +23,7 @@
 #include "soa/service/epoller.h"
 #include <map>
 #include <mutex>
+#include <atomic>
 
 
 namespace Datacratic {
@@ -108,6 +109,7 @@ struct EndpointBase : public Epoller {
      */
     std::vector<double> totalSleepSeconds() const { return totalSleepTime; }
     std::vector<rusage> getResourceUsage() const {
+        resourceEpoch++;
         std::vector<rusage> result;
         std::lock_guard<std::mutex> guard(usageLock);
         result = resourceUsage;
@@ -280,6 +282,7 @@ struct EndpointBase : public Epoller {
     std::vector<double> totalSleepTime;
     std::vector<rusage> resourceUsage;
     mutable std::mutex usageLock;
+    mutable std::atomic<int> resourceEpoch;
 
     /** Run a thread to handle events. */
     void runEventThread(int threadNum, int numThreads);