[Profiler] Force waiting for the LibrariesInfoCache service to be fully started (#6338)

Author: gleocadie

profiler/src/ProfilerEngine/Datadog.Profiler.Native.Linux/AutoResetEvent.h

@@ -21,6 +21,14 @@ class AutoResetEvent
     ~AutoResetEvent();
 
     void Set();
+
+    // Wait will block the execution of the thread until a call to Set is made
+    // or until it times out.
+    // [parameter] timeout : time to wait before returning.
+    //   if timeout == InfiniteTimeout, it will wait until Set is called.
+    //   if timeout != InfiniteTimeout, it will wait either for a call to Set either for the timeout.
+    // [Return]
+    //   true if Set was called, false is the call timed out.
     bool Wait(std::chrono::milliseconds timeout = InfiniteTimeout);
 
 private:

profiler/src/ProfilerEngine/Datadog.Profiler.Native.Linux/LibrariesInfoCache.cpp

@@ -33,8 +33,12 @@ bool LibrariesInfoCache::StartImpl()
     _librariesInfo.reserve(100);
     s_instance = this;
     unw_set_iterate_phdr_function(unw_local_addr_space, LibrariesInfoCache::DlIteratePhdr);
-    _worker = std::thread(&LibrariesInfoCache::Work, this);
-    return true;
+    auto startEvent = std::make_shared<AutoResetEvent>(false);
+    _worker = std::thread(&LibrariesInfoCache::Work, this, startEvent);
+    // We must wait for the thread to be fully started and the cache populated
+    // before reporting the service start status.
+    // 2s for CI
+    return startEvent->Wait(2s);
 }
 
 bool LibrariesInfoCache::StopImpl()
@@ -51,7 +55,7 @@ bool LibrariesInfoCache::StopImpl()
     return true;
 }
 
-void LibrariesInfoCache::Work()
+void LibrariesInfoCache::Work(std::shared_ptr<AutoResetEvent> startEvent)
 {
     OpSysTools::SetNativeThreadName(WStr("DD_LibsCache"));
 
@@ -80,6 +84,12 @@ void LibrariesInfoCache::Work()
         }
 
         UpdateCache();
+
+        if (startEvent != nullptr)
+        {
+            startEvent->Set();
+            startEvent.reset();
+        }
     }
 
     Log::Debug("Stopping worker: stop request received.");

profiler/src/ProfilerEngine/Datadog.Profiler.Native.Linux/LibrariesInfoCache.h

@@ -13,6 +13,7 @@
 #include <atomic>
 #include <libunwind.h>
 #include <link.h>
+#include <memory>
 #include <shared_mutex>
 #include <thread>
 #include <vector>
@@ -48,7 +49,7 @@ class LibrariesInfoCache : public ServiceBase
 #ifdef DD_TEST
 private:
 #endif
-    void Work();
+    void Work(std::shared_ptr<AutoResetEvent> startEvent);
 
     static LibrariesInfoCache* s_instance;