Cache method signatures in EDOObject.

This change introduces a thread-safe cache within `EDOObject` to store method signatures. When `methodSignatureForSelector:` is called, it first checks the cache. If the signature is not found, a remote request is made, and the result is then added to the cache for future use. This reduces redundant remote calls for method signature lookups.

This should improve overall edo performance.

PiperOrigin-RevId: 822643324

Author: Dave MacLachlan

Service/Sources/EDOObject+Invocation.m

@@ -29,6 +29,7 @@
 #import "Service/Sources/EDOParameter.h"
 #import "Service/Sources/EDORemoteException.h"
 #import "Service/Sources/EDOServicePort.h"
+#import "Service/Sources/EDOServiceRequest.h"
 
 static EDORemoteException *RemoteExceptionWithLocalInformation(EDORemoteException *remoteException,
                                                                EDOObject *target,
@@ -66,6 +67,46 @@
                                  callStackSymbols:fullStackTraces];
 }
 
+// The cache of the instance method signatures.
+static NSCache<NSString *, NSMethodSignature *> *gEDOInstanceMethodSignatureCache;
+
+/**
+ * Builds the key for the instance method signature cache.
+ *
+ * @param selector The selector.
+ * @param className The class name.
+ * @return The key.
+ */
+static NSString *EDOCreateMethodSignatureCacheKey(SEL selector, NSString *className) {
+  return [NSString stringWithFormat:@"%@-%@", className, NSStringFromSelector(selector)];
+}
+
+/**
+ * Gets the instance method signature for the given selector and class name from the cache.
+ *
+ * @param selector The selector.
+ * @param className The class name.
+ * @return The instance method signature.
+ */
+static NSMethodSignature *EDOInstanceMethodSignatureForSelector(SEL selector, NSString *className) {
+  NSString *key = EDOCreateMethodSignatureCacheKey(selector, className);
+  NSMethodSignature *methodSignature = [gEDOInstanceMethodSignatureCache objectForKey:key];
+  return methodSignature;
+}
+
+/**
+ * Adds the instance method signature for the given selector and class name to the cache.
+ *
+ * @param methodSignature The method signature.
+ * @param selector The selector.
+ * @param className The class name.
+ */
+static void EDOAddInstanceMethodSignature(NSMethodSignature *methodSignature, SEL selector,
+                                          NSString *className) {
+  NSString *key = EDOCreateMethodSignatureCacheKey(selector, className);
+  [gEDOInstanceMethodSignatureCache setObject:methodSignature forKey:key];
+}
+
 /**
  * The extension of EDOObject to handle the message forwarding.
  *
@@ -81,6 +122,12 @@
  */
 @implementation EDOObject (Invocation)
 
++ (void)initialize {
+  if (self == [EDOObject class]) {
+    gEDOInstanceMethodSignatureCache = [[NSCache alloc] init];
+  }
+}
+
 /**
  * Get an instance method signature for the @c EDOObject
  *
@@ -91,15 +138,23 @@ @implementation EDOObject (Invocation)
  * @return         The instance method signature.
  */
 - (NSMethodSignature *)methodSignatureForSelector:(SEL)selector {
-  // TODO(haowoo): Cache the signature.
+  NSString *className = self.className;
+  NSMethodSignature *signature = EDOInstanceMethodSignatureForSelector(selector, className);
+  if (signature) {
+    return signature;
+  }
   EDOServiceRequest *request = [EDOMethodSignatureRequest requestWithObject:self.remoteAddress
                                                                        port:self.servicePort
                                                                    selector:selector];
   EDOMethodSignatureResponse *response = (EDOMethodSignatureResponse *)[EDOClientService
       sendSynchronousRequest:request
                       onPort:self.servicePort.hostPort];
-  NSString *signature = response.signature;
-  return signature ? [NSMethodSignature signatureWithObjCTypes:signature.UTF8String] : nil;
+  NSString *signatureString = response.signature;
+  if (signatureString) {
+    signature = [NSMethodSignature signatureWithObjCTypes:signatureString.UTF8String];
+    EDOAddInstanceMethodSignature(signature, selector, className);
+  }
+  return signature;
 }
 
 /** Forwards the invocation to the remote. */