Implement parallel health checks

\n\nCommit migrated from f14a45e096

src/HealthChecks/HealthChecks/src/DefaultHealthCheckService.cs

@@ -39,23 +39,8 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
             Func<HealthCheckRegistration, bool> predicate,
             CancellationToken cancellationToken = default)
         {
-            var registrations = _options.Value.Registrations;
+            async Task<(string registrationName, HealthReportEntry result)> RunCheckAsync(IServiceScope scope, HealthCheckRegistration registration)
-
-            using (var scope = _scopeFactory.CreateScope())
             {
-                var context = new HealthCheckContext();
-                var entries = new Dictionary<string, HealthReportEntry>(StringComparer.OrdinalIgnoreCase);
-
-                var totalTime = ValueStopwatch.StartNew();
-                Log.HealthCheckProcessingBegin(_logger);
-
-                foreach (var registration in registrations)
-                {
-                    if (predicate != null && !predicate(registration))
-                    {
-                        continue;
-                    }
-
                 cancellationToken.ThrowIfCancellationRequested();
 
                 var healthCheck = registration.Factory(scope.ServiceProvider);
@@ -65,7 +50,7 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
                 using (_logger.BeginScope(new HealthCheckLogScope(registration.Name)))
                 {
                     var stopwatch = ValueStopwatch.StartNew();
-                        context.Registration = registration;
+                    var context = new HealthCheckContext { Registration = registration };
 
                     Log.HealthCheckBegin(_logger, registration);
 
@@ -100,16 +85,36 @@ namespace Microsoft.Extensions.Diagnostics.HealthChecks
                         Log.HealthCheckError(_logger, registration, ex, duration);
                     }
 
-                        entries[registration.Name] = entry;
+                    return (registration.Name, entry);
                 }
             }
 
+            IEnumerable<HealthCheckRegistration> registrations = _options.Value.Registrations;
+            if (predicate != null)
+            {
+                registrations = registrations.Where(predicate);
+            }
+
+            var totalTime = ValueStopwatch.StartNew();
+            Log.HealthCheckProcessingBegin(_logger);
+
+            (string registrationName, HealthReportEntry result)[] results;
+            using (var scope = _scopeFactory.CreateScope())
+            {
+                results = await Task.WhenAll(registrations.Select(r => RunCheckAsync(scope, r)));
+            }
+
+            var entries = new Dictionary<string, HealthReportEntry>(StringComparer.OrdinalIgnoreCase);
+            foreach (var (registrationName, result) in results)
+            {
+                entries[registrationName] = result;
+            }
+
             var totalElapsedTime = totalTime.GetElapsedTime();
             var report = new HealthReport(entries, totalElapsedTime);
             Log.HealthCheckProcessingEnd(_logger, report.Status, totalElapsedTime);
             return report;
         }
-        }
 
         private static void ValidateRegistrations(IEnumerable<HealthCheckRegistration> registrations)
         {