Runtime: Refactor conformance cache initialization to include installation of the dyld callbacks.

This more cleanly groups together the initialization steps needed to warm up the conformance cache, so redundant work doesn't need to be done by other interested parties (such as the type-by-name lookup @lhoward's working on).

Author: jckarter

stdlib/public/runtime/Casting.cpp

@@ -2397,6 +2397,8 @@ namespace {
 
 // Conformance Cache.
 
+static void _initializeCallbacksToInspectDylib();
+
 struct ConformanceState {
   ConcurrentMap<size_t, ConformanceCacheEntry> Cache;
   std::vector<ConformanceSection> SectionsToScan;
@@ -2405,24 +2407,18 @@ struct ConformanceState {
   ConformanceState() {
     SectionsToScan.reserve(16);
     pthread_mutex_init(&SectionsToScanLock, nullptr);
+    _initializeCallbacksToInspectDylib();
   }
 };
 
 static Lazy<ConformanceState> Conformances;
 
-// This variable is used to signal when a cache was generated and
-// it is correct to avoid a new scan.
-static unsigned ConformanceCacheGeneration = 0;
-
-void
-swift::swift_registerProtocolConformances(const ProtocolConformanceRecord *begin,
-                                          const ProtocolConformanceRecord *end){
-  auto &C = Conformances.get();
-
+static void
+_registerProtocolConformances(ConformanceState &C,
+                              const ProtocolConformanceRecord *begin,
+                              const ProtocolConformanceRecord *end) {
   pthread_mutex_lock(&C.SectionsToScanLock);
-
   C.SectionsToScan.push_back(ConformanceSection{begin, end});
-
   pthread_mutex_unlock(&C.SectionsToScanLock);
 }
 
@@ -2437,7 +2433,10 @@ static void _addImageProtocolConformancesBlock(const uint8_t *conformances,
   auto recordsEnd
     = reinterpret_cast<const ProtocolConformanceRecord*>
                                             (conformances + conformancesSize);
-  swift_registerProtocolConformances(recordsBegin, recordsEnd);
+  
+  // Conformance cache should always be sufficiently initialized by this point.
+  _registerProtocolConformances(Conformances.unsafeGetAlreadyInitialized(),
+                                recordsBegin, recordsEnd);
 }
 
 #if defined(__APPLE__) && defined(__MACH__)
@@ -2490,26 +2489,32 @@ static int _addImageProtocolConformances(struct dl_phdr_info *info,
 }
 #endif
 
-static void installCallbacksToInspectDylib() {
-  static OnceToken_t token;
-  auto callback = [](void*) {
-  #if defined(__APPLE__) && defined(__MACH__)
-    // Install our dyld callback if we haven't already.
-    // Dyld will invoke this on our behalf for all images that have already
-    // been loaded.
-    _dyld_register_func_for_add_image(_addImageProtocolConformances);
-  #elif defined(__ELF__)
-    // Search the loaded dls. Unlike the above, this only searches the already
-    // loaded ones.
-    // FIXME: Find a way to have this continue to happen after.
-    // rdar://problem/19045112
-    dl_iterate_phdr(_addImageProtocolConformances, nullptr);
-  #else
-  # error No known mechanism to inspect dynamic libraries on this platform.
-  #endif
-  };
-  
-  SWIFT_ONCE_F(token, callback, nullptr);
+static void _initializeCallbacksToInspectDylib() {
+#if defined(__APPLE__) && defined(__MACH__)
+  // Install our dyld callback.
+  // Dyld will invoke this on our behalf for all images that have already
+  // been loaded.
+  _dyld_register_func_for_add_image(_addImageProtocolConformances);
+#elif defined(__ELF__)
+  // Search the loaded dls. Unlike the above, this only searches the already
+  // loaded ones.
+  // FIXME: Find a way to have this continue to happen after.
+  // rdar://problem/19045112
+  dl_iterate_phdr(_addImageProtocolConformances, nullptr);
+#else
+# error No known mechanism to inspect dynamic libraries on this platform.
+#endif
+}
+
+// This variable is used to signal when a cache was generated and
+// it is correct to avoid a new scan.
+static unsigned ConformanceCacheGeneration = 0;
+
+void
+swift::swift_registerProtocolConformances(const ProtocolConformanceRecord *begin,
+                                          const ProtocolConformanceRecord *end){
+  auto &C = Conformances.get();
+  _registerProtocolConformances(C, begin, end);
 }
 
 static size_t hashTypeProtocolPair(const void *type,
@@ -2630,7 +2635,6 @@ swift::swift_conformsToProtocol(const Metadata *type,
 
   // Install callbacks for tracking when a new dylib is loaded so we can
   // scan it.
-  installCallbacksToInspectDylib();
   auto origType = type;
 
   unsigned numSections = 0;