Refactor channel pool

src/objective-c/GRPCClient/GRPCCall+ChannelArg.m

@@ -18,7 +18,7 @@
 
 #import "GRPCCall+ChannelArg.h"
 
-#import "private/GRPCChannel.h"
+#import "private/GRPCChannelPool.h"
 #import "private/GRPCHost.h"
 
 #import <grpc/impl/codegen/compression_types.h>
@@ -36,7 +36,7 @@
 }
 
 + (void)closeOpenConnections {
-  [GRPCChannel closeOpenConnections];
+  [GRPCChannelPool closeOpenConnections];
 }
 
 + (void)setDefaultCompressMethod:(GRPCCompressAlgorithm)algorithm forhost:(nonnull NSString *)host {

src/objective-c/GRPCClient/private/GRPCChannel.h

@@ -20,11 +20,37 @@
 
 #include <grpc/grpc.h>
 
+@protocol GRPCChannelFactory;
+
 @class GRPCCompletionQueue;
 @class GRPCCallOptions;
 @class GRPCChannelConfiguration;
 struct grpc_channel_credentials;
 
+NS_ASSUME_NONNULL_BEGIN
+
+/** Caching signature of a channel. */
+@interface GRPCChannelConfiguration : NSObject<NSCopying>
+
+/** The host that this channel is connected to. */
+@property(copy, readonly) NSString *host;
+
+/**
+ * Options of the corresponding call. Note that only the channel-related options are of interest to
+ * this class.
+ */
+@property(strong, readonly) GRPCCallOptions *callOptions;
+
+/** Acquire the factory to generate a new channel with current configurations. */
+@property(readonly) id<GRPCChannelFactory> channelFactory;
+
+/** Acquire the dictionary of channel args with current configurations. */
+@property(copy, readonly) NSDictionary *channelArgs;
+
+- (nullable instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions;
+
+@end
+
 /**
  * Each separate instance of this class represents at least one TCP connection to the provided host.
  */
@@ -35,40 +61,45 @@ struct grpc_channel_credentials;
 + (nullable instancetype) new NS_UNAVAILABLE;
 
 /**
- * Returns a channel connecting to \a host with options as \a callOptions. The channel may be new
- * or a cached channel that is already connected.
+ * Create a channel with remote \a host and signature \a channelConfigurations. Destroy delay is
+ * defaulted to 30 seconds.
  */
-+ (nullable instancetype)channelWithHost:(nonnull NSString *)host
-                             callOptions:(nullable GRPCCallOptions *)callOptions;
+- (nullable instancetype)initWithChannelConfiguration:(GRPCChannelConfiguration *)channelConfiguration;
 
 /**
- * Create a channel object with the signature \a config.
+ * Create a channel with remote \a host, signature \a channelConfigurations, and destroy delay of
+ * \a destroyDelay.
  */
-+ (nullable instancetype)createChannelWithConfiguration:(nonnull GRPCChannelConfiguration *)config;
+- (nullable instancetype)initWithChannelConfiguration:(GRPCChannelConfiguration *)channelConfiguration
+                         destroyDelay:(NSTimeInterval)destroyDelay NS_DESIGNATED_INITIALIZER;
 
 /**
- * Get a grpc core call object from this channel.
+ * Create a grpc core call object from this channel. The channel's refcount is added by 1. If no
+ * call is created, NULL is returned, and if the reason is because the channel is already
+ * disconnected, \a disconnected is set to YES. When the returned call is unreffed, the caller is
+ * obligated to call \a unref method once. \a disconnected may be null.
  */
-- (nullable grpc_call *)unmanagedCallWithPath:(nonnull NSString *)path
-                              completionQueue:(nonnull GRPCCompletionQueue *)queue
-                                  callOptions:(nonnull GRPCCallOptions *)callOptions;
+- (nullable grpc_call *)unmanagedCallWithPath:(NSString *)path
+                              completionQueue:(GRPCCompletionQueue *)queue
+                                  callOptions:(GRPCCallOptions *)callOptions
+                                 disconnected:(BOOL * _Nullable)disconnected;
 
 /**
- * Increase the refcount of the channel. If the channel was timed to be destroyed, cancel the timer.
+ * Unref the channel when a call is done. It also decreases the channel's refcount. If the refcount
+ * of the channel decreases to 0, the channel is destroyed after the destroy delay.
  */
-- (void)ref;
+- (void)unref;
 
 /**
- * Decrease the refcount of the channel. If the refcount of the channel decrease to 0, the channel
- * is destroyed after 30 seconds.
+ * Force the channel to be disconnected and destroyed.
  */
-- (void)unref;
+- (void)disconnect;
 
 /**
- * Force the channel to be disconnected and destroyed immediately.
+ * Return whether the channel is already disconnected.
  */
-- (void)disconnect;
+@property(readonly) BOOL disconnected;
 
-// TODO (mxyan): deprecate with GRPCCall:closeOpenConnections
-+ (void)closeOpenConnections;
 @end
+
+NS_ASSUME_NONNULL_END

src/objective-c/GRPCClient/private/GRPCChannel.m

@@ -28,139 +28,220 @@
 #import "GRPCInsecureChannelFactory.h"
 #import "GRPCSecureChannelFactory.h"
 #import "version.h"
+#import "../internal/GRPCCallOptions+Internal.h"
 
 #import <GRPCClient/GRPCCall+Cronet.h>
 #import <GRPCClient/GRPCCallOptions.h>
 
 /** When all calls of a channel are destroyed, destroy the channel after this much seconds. */
-NSTimeInterval kChannelDestroyDelay = 30;
+NSTimeInterval kDefaultChannelDestroyDelay = 30;
 
-/** Global instance of channel pool. */
-static GRPCChannelPool *gChannelPool;
+@implementation GRPCChannelConfiguration
 
-/**
- * Time the channel destroy when the channel's calls are unreffed. If there's new call, reset the
- * timer.
- */
-@interface GRPCChannelRef : NSObject
-
-- (instancetype)initWithDestroyDelay:(NSTimeInterval)destroyDelay
-              destroyChannelCallback:(void (^)())destroyChannelCallback;
+- (nullable instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions {
+  NSAssert(host.length, @"Host must not be empty.");
+  NSAssert(callOptions, @"callOptions must not be empty.");
+  if ((self = [super init])) {
+    _host = [host copy];
+    _callOptions = [callOptions copy];
+  }
+  return self;
+}
 
-/** Add call ref count to the channel and maybe reset the timer. */
-- (void)refChannel;
+- (id<GRPCChannelFactory>)channelFactory {
+  NSError *error;
+  id<GRPCChannelFactory> factory;
+  GRPCTransportType type = _callOptions.transportType;
+  switch (type) {
+    case GRPCTransportTypeChttp2BoringSSL:
+      // TODO (mxyan): Remove when the API is deprecated
+#ifdef GRPC_COMPILE_WITH_CRONET
+      if (![GRPCCall isUsingCronet]) {
+#endif
+        factory = [GRPCSecureChannelFactory
+                   factoryWithPEMRootCertificates:_callOptions.PEMRootCertificates
+                   privateKey:_callOptions.PEMPrivateKey
+                   certChain:_callOptions.PEMCertChain
+                   error:&error];
+        if (factory == nil) {
+          NSLog(@"Error creating secure channel factory: %@", error);
+        }
+        return factory;
+#ifdef GRPC_COMPILE_WITH_CRONET
+      }
+#endif
+      // fallthrough
+    case GRPCTransportTypeCronet:
+      return [GRPCCronetChannelFactory sharedInstance];
+    case GRPCTransportTypeInsecure:
+      return [GRPCInsecureChannelFactory sharedInstance];
+  }
+}
 
-/** Reduce call ref count to the channel and maybe set the timer. */
-- (void)unrefChannel;
+- (NSDictionary *)channelArgs {
+  NSMutableDictionary *args = [NSMutableDictionary new];
 
-/** Disconnect the channel. Any further ref/unref are discarded. */
-- (void)disconnect;
+  NSString *userAgent = @"grpc-objc/" GRPC_OBJC_VERSION_STRING;
+  NSString *userAgentPrefix = _callOptions.userAgentPrefix;
+  if (userAgentPrefix) {
+    args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] =
+    [_callOptions.userAgentPrefix stringByAppendingFormat:@" %@", userAgent];
+  } else {
+    args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] = userAgent;
+  }
 
-@end
+  NSString *hostNameOverride = _callOptions.hostNameOverride;
+  if (hostNameOverride) {
+    args[@GRPC_SSL_TARGET_NAME_OVERRIDE_ARG] = hostNameOverride;
+  }
 
-@implementation GRPCChannelRef {
-  NSTimeInterval _destroyDelay;
-  void (^_destroyChannelCallback)();
+  if (_callOptions.responseSizeLimit) {
+    args[@GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH] =
+    [NSNumber numberWithUnsignedInteger:_callOptions.responseSizeLimit];
+  }
 
-  NSUInteger _refCount;
-  BOOL _disconnected;
-  dispatch_queue_t _dispatchQueue;
+  if (_callOptions.compressionAlgorithm != GRPC_COMPRESS_NONE) {
+    args[@GRPC_COMPRESSION_CHANNEL_DEFAULT_ALGORITHM] =
+    [NSNumber numberWithInt:_callOptions.compressionAlgorithm];
+  }
 
-  /**
-   * Date and time when last timer is scheduled. If a firing timer's scheduled date is different
-   * from this, it is discarded.
-   */
-  NSDate *_lastDispatch;
-}
+  if (_callOptions.keepaliveInterval != 0) {
+    args[@GRPC_ARG_KEEPALIVE_TIME_MS] =
+    [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.keepaliveInterval * 1000)];
+    args[@GRPC_ARG_KEEPALIVE_TIMEOUT_MS] =
+    [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.keepaliveTimeout * 1000)];
+  }
 
-- (instancetype)initWithDestroyDelay:(NSTimeInterval)destroyDelay
-              destroyChannelCallback:(void (^)())destroyChannelCallback {
-  if ((self = [super init])) {
-    _destroyDelay = destroyDelay;
-    _destroyChannelCallback = destroyChannelCallback;
+  if (_callOptions.retryEnabled == NO) {
+    args[@GRPC_ARG_ENABLE_RETRIES] = [NSNumber numberWithInt:_callOptions.retryEnabled];
+  }
 
-    _refCount = 1;
-    _disconnected = NO;
-    if (@available(iOS 8.0, *)) {
-      _dispatchQueue = dispatch_queue_create(
-          NULL,
-          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
-    } else {
-      _dispatchQueue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
+  if (_callOptions.connectMinTimeout > 0) {
+    args[@GRPC_ARG_MIN_RECONNECT_BACKOFF_MS] =
+    [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectMinTimeout * 1000)];
   }
-    _lastDispatch = nil;
+  if (_callOptions.connectInitialBackoff > 0) {
+    args[@GRPC_ARG_INITIAL_RECONNECT_BACKOFF_MS] = [NSNumber
+                                                    numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectInitialBackoff * 1000)];
   }
-  return self;
-}
-
-- (void)refChannel {
-  dispatch_async(_dispatchQueue, ^{
-    if (!self->_disconnected) {
-      self->_refCount++;
-      self->_lastDispatch = nil;
+  if (_callOptions.connectMaxBackoff > 0) {
+    args[@GRPC_ARG_MAX_RECONNECT_BACKOFF_MS] =
+    [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectMaxBackoff * 1000)];
   }
-  });
-}
 
-- (void)unrefChannel {
-  dispatch_async(_dispatchQueue, ^{
-    if (!self->_disconnected) {
-      self->_refCount--;
-      if (self->_refCount == 0) {
-        NSDate *now = [NSDate date];
-        self->_lastDispatch = now;
-        dispatch_time_t delay =
-            dispatch_time(DISPATCH_TIME_NOW, (int64_t)self->_destroyDelay * NSEC_PER_SEC);
-        dispatch_after(delay, self->_dispatchQueue, ^{
-          [self timedDisconnectWithScheduleDate:now];
-        });
+  if (_callOptions.logContext != nil) {
+    args[@GRPC_ARG_MOBILE_LOG_CONTEXT] = _callOptions.logContext;
   }
+
+  if (_callOptions.channelPoolDomain.length != 0) {
+    args[@GRPC_ARG_CHANNEL_POOL_DOMAIN] = _callOptions.channelPoolDomain;
   }
-  });
+
+  [args addEntriesFromDictionary:_callOptions.additionalChannelArgs];
+
+  return args;
 }
 
-- (void)disconnect {
-  dispatch_async(_dispatchQueue, ^{
-    if (!self->_disconnected) {
-      self->_lastDispatch = nil;
-      self->_disconnected = YES;
-      // Break retain loop
-      self->_destroyChannelCallback = nil;
-    }
-  });
+- (nonnull id)copyWithZone:(nullable NSZone *)zone {
+  GRPCChannelConfiguration *newConfig =
+  [[GRPCChannelConfiguration alloc] initWithHost:_host callOptions:_callOptions];
+
+  return newConfig;
 }
 
-- (void)timedDisconnectWithScheduleDate:(NSDate *)scheduleDate {
-  dispatch_async(_dispatchQueue, ^{
-    if (self->_disconnected || self->_lastDispatch != scheduleDate) {
-      return;
+- (BOOL)isEqual:(id)object {
+  if (![object isKindOfClass:[GRPCChannelConfiguration class]]) {
+    return NO;
   }
-    self->_lastDispatch = nil;
-    self->_disconnected = YES;
-    self->_destroyChannelCallback();
-    // Break retain loop
-    self->_destroyChannelCallback = nil;
-  });
+  GRPCChannelConfiguration *obj = (GRPCChannelConfiguration *)object;
+  if (!(obj.host == _host || (_host != nil && [obj.host isEqualToString:_host]))) return NO;
+  if (!(obj.callOptions == _callOptions || [obj.callOptions hasChannelOptionsEqualTo:_callOptions]))
+    return NO;
+
+  return YES;
+}
+
+- (NSUInteger)hash {
+  NSUInteger result = 0;
+  result ^= _host.hash;
+  result ^= _callOptions.channelOptionsHash;
+
+  return result;
 }
 
 @end
 
+
+
 @implementation GRPCChannel {
   GRPCChannelConfiguration *_configuration;
-  grpc_channel *_unmanagedChannel;
-  GRPCChannelRef *_channelRef;
+
   dispatch_queue_t _dispatchQueue;
+  grpc_channel *_unmanagedChannel;
+  NSTimeInterval _destroyDelay;
+
+  NSUInteger _refcount;
+  NSDate *_lastDispatch;
+}
+@synthesize disconnected = _disconnected;
+
+- (nullable instancetype)initWithChannelConfiguration:(GRPCChannelConfiguration *)channelConfiguration {
+  return [self initWithChannelConfiguration:channelConfiguration
+                               destroyDelay:kDefaultChannelDestroyDelay];
+}
+
+- (nullable instancetype)initWithChannelConfiguration:(GRPCChannelConfiguration *)channelConfiguration
+                                         destroyDelay:(NSTimeInterval)destroyDelay {
+  NSAssert(channelConfiguration, @"channelConfiguration must not be empty.");
+  NSAssert(destroyDelay > 0, @"destroyDelay must be greater than 0.");
+  if ((self = [super init])) {
+    _configuration = [channelConfiguration copy];
+    if (@available(iOS 8.0, *)) {
+      _dispatchQueue = dispatch_queue_create(
+                                             NULL,
+                                             dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
+    } else {
+      _dispatchQueue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
+    }
+
+    // Create gRPC core channel object.
+    NSString *host = channelConfiguration.host;
+    NSAssert(host.length != 0, @"host cannot be nil");
+    NSDictionary *channelArgs;
+    if (channelConfiguration.callOptions.additionalChannelArgs.count != 0) {
+      NSMutableDictionary *args = [channelConfiguration.channelArgs mutableCopy];
+      [args addEntriesFromDictionary:channelConfiguration.callOptions.additionalChannelArgs];
+      channelArgs = args;
+    } else {
+      channelArgs = channelConfiguration.channelArgs;
+    }
+    id<GRPCChannelFactory> factory = channelConfiguration.channelFactory;
+    _unmanagedChannel = [factory createChannelWithHost:host channelArgs:channelArgs];
+    if (_unmanagedChannel == NULL) {
+      NSLog(@"Unable to create channel.");
+      return nil;
+    }
+    _destroyDelay = destroyDelay;
+    _disconnected = NO;
+  }
+  return self;
 }
 
 - (grpc_call *)unmanagedCallWithPath:(NSString *)path
                      completionQueue:(GRPCCompletionQueue *)queue
-                         callOptions:(GRPCCallOptions *)callOptions {
+                         callOptions:(GRPCCallOptions *)callOptions
+                        disconnected:(BOOL *)disconnected {
   NSAssert(path.length, @"path must not be empty.");
   NSAssert(queue, @"completionQueue must not be empty.");
   NSAssert(callOptions, @"callOptions must not be empty.");
-  __block grpc_call *call = nil;
+  __block BOOL isDisconnected = NO;
+  __block grpc_call *call = NULL;
   dispatch_sync(_dispatchQueue, ^{
-    if (self->_unmanagedChannel) {
+    if (self->_disconnected) {
+      isDisconnected = YES;
+    } else {
+      NSAssert(self->_unmanagedChannel != NULL, @"Invalid channel.");
+
       NSString *serverAuthority =
       callOptions.transportType == GRPCTransportTypeCronet ? nil : callOptions.serverAuthority;
       NSTimeInterval timeout = callOptions.timeout;
@@ -182,71 +263,64 @@ static GRPCChannelPool *gChannelPool;
         grpc_slice_unref(host_slice);
       }
       grpc_slice_unref(path_slice);
+      if (call == NULL) {
+        NSLog(@"Unable to create call.");
       } else {
-      NSAssert(self->_unmanagedChannel != nil, @"Invalid channeg.");
+        // Ref the channel;
+        [self ref];
+      }
     }
   });
+  if (disconnected != nil) {
+    *disconnected = isDisconnected;
+  }
   return call;
 }
 
+// This function should be called on _dispatchQueue.
 - (void)ref {
-  dispatch_async(_dispatchQueue, ^{
-    if (self->_unmanagedChannel) {
-      [self->_channelRef refChannel];
+  _refcount++;
+  if (_refcount == 1 && _lastDispatch != nil) {
+    _lastDispatch = nil;
   }
-  });
 }
 
 - (void)unref {
   dispatch_async(_dispatchQueue, ^{
-    if (self->_unmanagedChannel) {
-      [self->_channelRef unrefChannel];
+    self->_refcount--;
+    if (self->_refcount == 0 && !self->_disconnected) {
+      // Start timer.
+      dispatch_time_t delay =
+          dispatch_time(DISPATCH_TIME_NOW, (int64_t)self->_destroyDelay * NSEC_PER_SEC);
+      NSDate *now = [NSDate date];
+      self->_lastDispatch = now;
+      dispatch_after(delay, self->_dispatchQueue, ^{
+        if (self->_lastDispatch == now) {
+          grpc_channel_destroy(self->_unmanagedChannel);
+          self->_unmanagedChannel = NULL;
+          self->_disconnected = YES;
         }
       });
-}
-
-- (void)disconnect {
-  dispatch_async(_dispatchQueue, ^{
-    if (self->_unmanagedChannel) {
-      grpc_channel_destroy(self->_unmanagedChannel);
-      self->_unmanagedChannel = nil;
-      [self->_channelRef disconnect];
     }
   });
 }
 
-- (void)destroyChannel {
+- (void)disconnect {
   dispatch_async(_dispatchQueue, ^{
-    if (self->_unmanagedChannel) {
+    if (!self->_disconnected) {
       grpc_channel_destroy(self->_unmanagedChannel);
       self->_unmanagedChannel = nil;
-      [gChannelPool removeChannel:self];
+      self->_disconnected = YES;
     }
   });
 }
 
-- (nullable instancetype)initWithUnmanagedChannel:(grpc_channel *_Nullable)unmanagedChannel
-                                    configuration:(GRPCChannelConfiguration *)configuration {
-  NSAssert(configuration, @"Configuration must not be empty.");
-  if (!unmanagedChannel) {
-    return nil;
-  }
-  if ((self = [super init])) {
-    _unmanagedChannel = unmanagedChannel;
-    _configuration = [configuration copy];
-    _channelRef = [[GRPCChannelRef alloc] initWithDestroyDelay:kChannelDestroyDelay
-                                        destroyChannelCallback:^{
-                                          [self destroyChannel];
-                                        }];
-    if (@available(iOS 8.0, *)) {
-      _dispatchQueue = dispatch_queue_create(
-          NULL,
-          dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_DEFAULT, -1));
-    } else {
-      _dispatchQueue = dispatch_queue_create(NULL, DISPATCH_QUEUE_SERIAL);
-    }
-  }
-  return self;
+- (BOOL)disconnected {
+  __block BOOL disconnected;
+  dispatch_sync(_dispatchQueue, ^{
+    disconnected = self->_disconnected;
+  });
+  return disconnected;
 }
 
 - (void)dealloc {
@@ -255,47 +329,4 @@ static GRPCChannelPool *gChannelPool;
   }
 }
 
-+ (nullable instancetype)createChannelWithConfiguration:(GRPCChannelConfiguration *)config {
-  NSAssert(config != nil, @"configuration cannot be empty");
-  NSString *host = config.host;
-  NSAssert(host.length != 0, @"host cannot be nil");
-
-  NSDictionary *channelArgs;
-  if (config.callOptions.additionalChannelArgs.count != 0) {
-    NSMutableDictionary *args = [config.channelArgs mutableCopy];
-    [args addEntriesFromDictionary:config.callOptions.additionalChannelArgs];
-    channelArgs = args;
-  } else {
-    channelArgs = config.channelArgs;
-  }
-  id<GRPCChannelFactory> factory = config.channelFactory;
-  grpc_channel *unmanaged_channel = [factory createChannelWithHost:host channelArgs:channelArgs];
-  return [[GRPCChannel alloc] initWithUnmanagedChannel:unmanaged_channel configuration:config];
-}
-
-+ (nullable instancetype)channelWithHost:(NSString *)host
-                             callOptions:(GRPCCallOptions *)callOptions {
-  static dispatch_once_t initChannelPool;
-  dispatch_once(&initChannelPool, ^{
-    gChannelPool = [[GRPCChannelPool alloc] init];
-  });
-
-  NSURL *hostURL = [NSURL URLWithString:[@"https://" stringByAppendingString:host]];
-  if (hostURL.host && !hostURL.port) {
-    host = [hostURL.host stringByAppendingString:@":443"];
-  }
-
-  GRPCChannelConfiguration *channelConfig =
-      [[GRPCChannelConfiguration alloc] initWithHost:host callOptions:callOptions];
-  if (channelConfig == nil) {
-    return nil;
-  }
-
-  return [gChannelPool channelWithConfiguration:channelConfig];
-}
-
-+ (void)closeOpenConnections {
-  [gChannelPool removeAndCloseAllChannels];
-}
-
 @end

src/objective-c/GRPCClient/private/GRPCChannelPool.h

@@ -29,48 +29,45 @@ NS_ASSUME_NONNULL_BEGIN
 
 @class GRPCChannel;
 
-/** Caching signature of a channel. */
-@interface GRPCChannelConfiguration : NSObject<NSCopying>
-
-/** The host that this channel is connected to. */
-@property(copy, readonly) NSString *host;
-
-/**
- * Options of the corresponding call. Note that only the channel-related options are of interest to
- * this class.
- */
-@property(strong, readonly) GRPCCallOptions *callOptions;
-
-/** Acquire the factory to generate a new channel with current configurations. */
-@property(readonly) id<GRPCChannelFactory> channelFactory;
-
-/** Acquire the dictionary of channel args with current configurations. */
-@property(copy, readonly) NSDictionary *channelArgs;
-
-- (nullable instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions;
-
-@end
-
 /**
  * Manage the pool of connected channels. When a channel is no longer referenced by any call,
  * destroy the channel after a certain period of time elapsed.
  */
 @interface GRPCChannelPool : NSObject
 
+/**
+ * Get the singleton instance
+ */
++ (nullable instancetype)sharedInstance;
+
 /**
  * Return a channel with a particular configuration. If the channel does not exist, execute \a
  * createChannel then add it in the pool. If the channel exists, increase its reference count.
  */
-- (GRPCChannel *)channelWithConfiguration:(GRPCChannelConfiguration *)configuration;
+- (GRPCChannel *)channelWithHost:(NSString *)host
+                     callOptions:(GRPCCallOptions *)callOptions;
+
+/**
+ * This method is deprecated.
+ *
+ * Destroy all open channels and close their connections.
+ */
++ (void)closeOpenConnections;
 
-/** Remove a channel from the pool. */
-- (void)removeChannel:(GRPCChannel *)channel;
+// Test-only methods below
 
-/** Clear all channels in the pool. */
-- (void)removeAllChannels;
+/**
+ * Return a channel with a special destroy delay. If \a destroyDelay is 0, use the default destroy
+ * delay.
+ */
+- (GRPCChannel *)channelWithHost:(NSString *)host
+                     callOptions:(GRPCCallOptions *)callOptions
+                    destroyDelay:(NSTimeInterval)destroyDelay;
 
-/** Clear all channels in the pool and destroy the channels. */
-- (void)removeAndCloseAllChannels;
+/**
+ * Simulate a network transition event and destroy all channels.
+ */
+- (void)destroyAllChannels;
 
 @end
 

src/objective-c/GRPCClient/private/GRPCChannelPool.m

@@ -33,145 +33,21 @@
 
 extern const char *kCFStreamVarName;
 
-@implementation GRPCChannelConfiguration
+static GRPCChannelPool *gChannelPool;
+static dispatch_once_t gInitChannelPool;
 
-- (nullable instancetype)initWithHost:(NSString *)host callOptions:(GRPCCallOptions *)callOptions {
-  NSAssert(host.length, @"Host must not be empty.");
-  NSAssert(callOptions, @"callOptions must not be empty.");
-  if ((self = [super init])) {
-    _host = [host copy];
-    _callOptions = [callOptions copy];
-  }
-  return self;
-}
-
-- (id<GRPCChannelFactory>)channelFactory {
-  NSError *error;
-  id<GRPCChannelFactory> factory;
-  GRPCTransportType type = _callOptions.transportType;
-  switch (type) {
-    case GRPCTransportTypeChttp2BoringSSL:
-      // TODO (mxyan): Remove when the API is deprecated
-#ifdef GRPC_COMPILE_WITH_CRONET
-      if (![GRPCCall isUsingCronet]) {
-#endif
-        factory = [GRPCSecureChannelFactory
-            factoryWithPEMRootCertificates:_callOptions.PEMRootCertificates
-                                privateKey:_callOptions.PEMPrivateKey
-                                 certChain:_callOptions.PEMCertChain
-                                     error:&error];
-        if (factory == nil) {
-          NSLog(@"Error creating secure channel factory: %@", error);
-        }
-        return factory;
-#ifdef GRPC_COMPILE_WITH_CRONET
-      }
-#endif
-      // fallthrough
-    case GRPCTransportTypeCronet:
-      return [GRPCCronetChannelFactory sharedInstance];
-    case GRPCTransportTypeInsecure:
-      return [GRPCInsecureChannelFactory sharedInstance];
-  }
-}
-
-- (NSDictionary *)channelArgs {
-  NSMutableDictionary *args = [NSMutableDictionary new];
-
-  NSString *userAgent = @"grpc-objc/" GRPC_OBJC_VERSION_STRING;
-  NSString *userAgentPrefix = _callOptions.userAgentPrefix;
-  if (userAgentPrefix) {
-    args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] =
-        [_callOptions.userAgentPrefix stringByAppendingFormat:@" %@", userAgent];
-  } else {
-    args[@GRPC_ARG_PRIMARY_USER_AGENT_STRING] = userAgent;
-  }
-
-  NSString *hostNameOverride = _callOptions.hostNameOverride;
-  if (hostNameOverride) {
-    args[@GRPC_SSL_TARGET_NAME_OVERRIDE_ARG] = hostNameOverride;
-  }
-
-  if (_callOptions.responseSizeLimit) {
-    args[@GRPC_ARG_MAX_RECEIVE_MESSAGE_LENGTH] =
-        [NSNumber numberWithUnsignedInteger:_callOptions.responseSizeLimit];
-  }
-
-  if (_callOptions.compressionAlgorithm != GRPC_COMPRESS_NONE) {
-    args[@GRPC_COMPRESSION_CHANNEL_DEFAULT_ALGORITHM] =
-        [NSNumber numberWithInt:_callOptions.compressionAlgorithm];
-  }
-
-  if (_callOptions.keepaliveInterval != 0) {
-    args[@GRPC_ARG_KEEPALIVE_TIME_MS] =
-        [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.keepaliveInterval * 1000)];
-    args[@GRPC_ARG_KEEPALIVE_TIMEOUT_MS] =
-        [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.keepaliveTimeout * 1000)];
-  }
-
-  if (_callOptions.retryEnabled == NO) {
-    args[@GRPC_ARG_ENABLE_RETRIES] = [NSNumber numberWithInt:_callOptions.retryEnabled];
-  }
-
-  if (_callOptions.connectMinTimeout > 0) {
-    args[@GRPC_ARG_MIN_RECONNECT_BACKOFF_MS] =
-        [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectMinTimeout * 1000)];
-  }
-  if (_callOptions.connectInitialBackoff > 0) {
-    args[@GRPC_ARG_INITIAL_RECONNECT_BACKOFF_MS] = [NSNumber
-        numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectInitialBackoff * 1000)];
-  }
-  if (_callOptions.connectMaxBackoff > 0) {
-    args[@GRPC_ARG_MAX_RECONNECT_BACKOFF_MS] =
-        [NSNumber numberWithUnsignedInteger:(NSUInteger)(_callOptions.connectMaxBackoff * 1000)];
-  }
-
-  if (_callOptions.logContext != nil) {
-    args[@GRPC_ARG_MOBILE_LOG_CONTEXT] = _callOptions.logContext;
-  }
-
-  if (_callOptions.channelPoolDomain.length != 0) {
-    args[@GRPC_ARG_CHANNEL_POOL_DOMAIN] = _callOptions.channelPoolDomain;
-  }
-
-  [args addEntriesFromDictionary:_callOptions.additionalChannelArgs];
-
-  return args;
-}
-
-- (nonnull id)copyWithZone:(nullable NSZone *)zone {
-  GRPCChannelConfiguration *newConfig =
-      [[GRPCChannelConfiguration alloc] initWithHost:_host callOptions:_callOptions];
-
-  return newConfig;
+@implementation GRPCChannelPool {
+  NSMutableDictionary<GRPCChannelConfiguration *, GRPCChannel *> *_channelPool;
 }
 
-- (BOOL)isEqual:(id)object {
-  if (![object isKindOfClass:[GRPCChannelConfiguration class]]) {
-    return NO;
++ (nullable instancetype)sharedInstance {
+  dispatch_once(&gInitChannelPool, ^{
+    gChannelPool = [[GRPCChannelPool alloc] init];
+    if (gChannelPool == nil) {
+      [NSException raise:NSMallocException format:@"Cannot initialize global channel pool."];
     }
-  GRPCChannelConfiguration *obj = (GRPCChannelConfiguration *)object;
-  if (!(obj.host == _host || (_host != nil && [obj.host isEqualToString:_host]))) return NO;
-  if (!(obj.callOptions == _callOptions || [obj.callOptions hasChannelOptionsEqualTo:_callOptions]))
-    return NO;
-
-  return YES;
-}
-
-- (NSUInteger)hash {
-  NSUInteger result = 0;
-  result ^= _host.hash;
-  result ^= _callOptions.channelOptionsHash;
-
-  return result;
-}
-
-@end
-
-#pragma mark GRPCChannelPool
-
-@implementation GRPCChannelPool {
-  NSMutableDictionary<GRPCChannelConfiguration *, GRPCChannel *> *_channelPool;
+  });
+  return gChannelPool;
 }
 
 - (instancetype)init {
@@ -187,61 +63,56 @@ extern const char *kCFStreamVarName;
   return self;
 }
 
-- (void)dealloc {
-  [GRPCConnectivityMonitor unregisterObserver:self];
+- (GRPCChannel *)channelWithHost:(NSString *)host
+                     callOptions:(GRPCCallOptions *)callOptions {
+  return [self channelWithHost:host
+                   callOptions:callOptions
+                  destroyDelay:0];
 }
 
-- (GRPCChannel *)channelWithConfiguration:(GRPCChannelConfiguration *)configuration {
-  NSAssert(configuration != nil, @"Must has a configuration");
+- (GRPCChannel *)channelWithHost:(NSString *)host
+                     callOptions:(GRPCCallOptions *)callOptions
+                    destroyDelay:(NSTimeInterval)destroyDelay {
+  NSAssert(host.length > 0, @"Host must not be empty.");
+  NSAssert(callOptions != nil, @"callOptions must not be empty.");
   GRPCChannel *channel;
+  GRPCChannelConfiguration *configuration =
+  [[GRPCChannelConfiguration alloc] initWithHost:host callOptions:callOptions];
   @synchronized(self) {
-    if ([_channelPool objectForKey:configuration]) {
     channel = _channelPool[configuration];
-      [channel ref];
+    if (channel == nil || channel.disconnected) {
+      if (destroyDelay == 0) {
+        channel = [[GRPCChannel alloc] initWithChannelConfiguration:configuration];
       } else {
-      channel = [GRPCChannel createChannelWithConfiguration:configuration];
-      if (channel != nil) {
-        _channelPool[configuration] = channel;
+        channel = [[GRPCChannel alloc] initWithChannelConfiguration:configuration destroyDelay:destroyDelay];
       }
+      _channelPool[configuration] = channel;
     }
   }
   return channel;
 }
 
-- (void)removeChannel:(GRPCChannel *)channel {
-  @synchronized(self) {
-    __block GRPCChannelConfiguration *keyToDelete = nil;
-    [_channelPool
-        enumerateKeysAndObjectsUsingBlock:^(GRPCChannelConfiguration *_Nonnull key,
-                                            GRPCChannel *_Nonnull obj, BOOL *_Nonnull stop) {
-          if (obj == channel) {
-            keyToDelete = key;
-            *stop = YES;
-          }
-        }];
-    [self->_channelPool removeObjectForKey:keyToDelete];
-  }
-}
 
-- (void)removeAllChannels {
-  @synchronized(self) {
-    _channelPool = [NSMutableDictionary dictionary];
-  }
+
++ (void)closeOpenConnections {
+  [[GRPCChannelPool sharedInstance] destroyAllChannels];
 }
 
-- (void)removeAndCloseAllChannels {
+- (void)destroyAllChannels {
   @synchronized(self) {
-    [_channelPool
-        enumerateKeysAndObjectsUsingBlock:^(GRPCChannelConfiguration *_Nonnull key,
-                                            GRPCChannel *_Nonnull obj, BOOL *_Nonnull stop) {
-          [obj disconnect];
-        }];
+    for (id key in _channelPool) {
+      [_channelPool[key] disconnect];
+    }
     _channelPool = [NSMutableDictionary dictionary];
   }
 }
 
 - (void)connectivityChange:(NSNotification *)note {
-  [self removeAndCloseAllChannels];
+  [self destroyAllChannels];
+}
+
+- (void)dealloc {
+  [GRPCConnectivityMonitor unregisterObserver:self];
 }
 
 @end

src/objective-c/GRPCClient/private/GRPCWrappedCall.m

@@ -24,6 +24,7 @@
 #include <grpc/support/alloc.h>
 
 #import "GRPCChannel.h"
+#import "GRPCChannelPool.h"
 #import "GRPCCompletionQueue.h"
 #import "GRPCHost.h"
 #import "NSData+GRPC.h"
@@ -256,13 +257,21 @@
     // consuming too many threads and having contention of multiple calls in a single completion
     // queue. Currently we use a singleton queue.
     _queue = [GRPCCompletionQueue completionQueue];
-    _channel = [GRPCChannel channelWithHost:host callOptions:callOptions];
+    BOOL disconnected;
+    do {
+      _channel = [[GRPCChannelPool sharedInstance] channelWithHost:host callOptions:callOptions];
       if (_channel == nil) {
         NSLog(@"Failed to get a channel for the host.");
         return nil;
       }
-    _call = [_channel unmanagedCallWithPath:path completionQueue:_queue callOptions:callOptions];
-    if (_call == NULL) {
+      _call = [_channel unmanagedCallWithPath:path
+                              completionQueue:_queue
+                                  callOptions:callOptions
+                                 disconnected:&disconnected];
+      // Try create another channel if the current channel is disconnected (due to idleness or
+      // connectivity monitor disconnection).
+    } while (_call == NULL && disconnected);
+    if (_call == nil) {
       NSLog(@"Failed to create a call.");
       return nil;
     }
@@ -317,6 +326,7 @@
 - (void)dealloc {
   if (_call) {
     grpc_call_unref(_call);
+    [_channel unref];
   }
   [_channel unref];
   _channel = nil;

src/objective-c/tests/ChannelTests/ChannelPoolTest.m

@@ -20,6 +20,7 @@
 
 #import "../../GRPCClient/private/GRPCChannel.h"
 #import "../../GRPCClient/private/GRPCChannelPool.h"
+#import "../../GRPCClient/private/GRPCCompletionQueue.h"
 
 #define TEST_TIMEOUT 32
 
@@ -35,92 +36,104 @@ NSString *kDummyHost = @"dummy.host";
   grpc_init();
 }
 
-- (void)testCreateChannel {
+- (void)testChannelPooling {
   NSString *kDummyHost = @"dummy.host";
+  NSString *kDummyHost2 = @"dummy.host2";
+
   GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeInsecure;
   GRPCCallOptions *options2 = [options1 copy];
-  GRPCChannelConfiguration *config1 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options1];
-  GRPCChannelConfiguration *config2 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options2];
-  GRPCChannelPool *pool = [[GRPCChannelPool alloc] init];
-
-  GRPCChannel *channel1 = [pool channelWithConfiguration:config1];
-  GRPCChannel *channel2 = [pool channelWithConfiguration:config2];
+  GRPCMutableCallOptions *options3 = [options2 mutableCopy];
+  options3.transportType = GRPCTransportTypeInsecure;
+
+  GRPCChannelPool *pool = [GRPCChannelPool sharedInstance];
+
+  GRPCChannel *channel1 = [pool channelWithHost:kDummyHost
+                                    callOptions:options1];
+  GRPCChannel *channel2 = [pool channelWithHost:kDummyHost
+                                    callOptions:options2];
+  GRPCChannel *channel3 = [pool channelWithHost:kDummyHost2
+                                    callOptions:options1];
+  GRPCChannel *channel4 = [pool channelWithHost:kDummyHost
+                                    callOptions:options3];
   XCTAssertEqual(channel1, channel2);
+  XCTAssertNotEqual(channel1, channel3);
+  XCTAssertNotEqual(channel1, channel4);
+  XCTAssertNotEqual(channel3, channel4);
 }
 
-- (void)testChannelRemove {
-  GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeInsecure;
-  GRPCChannelConfiguration *config1 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options1];
-  GRPCChannelPool *pool = [[GRPCChannelPool alloc] init];
-  GRPCChannel *channel1 = [pool channelWithConfiguration:config1];
-  [pool removeChannel:channel1];
-  GRPCChannel *channel2 = [pool channelWithConfiguration:config1];
-  XCTAssertNotEqual(channel1, channel2);
-}
-
-extern NSTimeInterval kChannelDestroyDelay;
+- (void)testDestroyAllChannels {
+  NSString *kDummyHost = @"dummy.host";
 
-- (void)testChannelTimeoutCancel {
-  NSTimeInterval kOriginalInterval = kChannelDestroyDelay;
-  kChannelDestroyDelay = 3.0;
-  GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeInsecure;
-  GRPCChannelConfiguration *config1 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options1];
-  GRPCChannelPool *pool = [[GRPCChannelPool alloc] init];
-  GRPCChannel *channel1 = [pool channelWithConfiguration:config1];
-  [channel1 unref];
-  sleep(1);
-  GRPCChannel *channel2 = [pool channelWithConfiguration:config1];
-  XCTAssertEqual(channel1, channel2);
-  sleep((int)kChannelDestroyDelay + 2);
-  GRPCChannel *channel3 = [pool channelWithConfiguration:config1];
-  XCTAssertEqual(channel1, channel3);
-  kChannelDestroyDelay = kOriginalInterval;
+  GRPCMutableCallOptions *options = [[GRPCMutableCallOptions alloc] init];
+  GRPCChannelPool *pool = [GRPCChannelPool sharedInstance];
+  GRPCChannel *channel = [pool channelWithHost:kDummyHost
+                                   callOptions:options];
+  grpc_call *call = [channel unmanagedCallWithPath:@"dummy.path"
+                                   completionQueue:[GRPCCompletionQueue completionQueue]
+                                       callOptions:options
+                                      disconnected:nil];
+  [pool destroyAllChannels];
+  XCTAssertTrue(channel.disconnected);
+  GRPCChannel *channel2 = [pool channelWithHost:kDummyHost
+                                    callOptions:options];
+  XCTAssertNotEqual(channel, channel2);
+  grpc_call_unref(call);
 }
 
-- (void)testChannelDisconnect {
+- (void)testGetChannelBeforeChannelTimedDisconnection {
   NSString *kDummyHost = @"dummy.host";
-  GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeInsecure;
-  GRPCCallOptions *options2 = [options1 copy];
-  GRPCChannelConfiguration *config1 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options1];
-  GRPCChannelConfiguration *config2 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options2];
-  GRPCChannelPool *pool = [[GRPCChannelPool alloc] init];
-
-  GRPCChannel *channel1 = [pool channelWithConfiguration:config1];
-  [pool removeAndCloseAllChannels];
-  GRPCChannel *channel2 = [pool channelWithConfiguration:config2];
-  XCTAssertNotEqual(channel1, channel2);
+  const NSTimeInterval kDestroyDelay = 1;
+
+  GRPCMutableCallOptions *options = [[GRPCMutableCallOptions alloc] init];
+  GRPCChannelPool *pool = [GRPCChannelPool sharedInstance];
+  GRPCChannel *channel = [pool channelWithHost:kDummyHost
+                                   callOptions:options
+                                  destroyDelay:kDestroyDelay];
+  grpc_call *call = [channel unmanagedCallWithPath:@"dummy.path"
+                                   completionQueue:[GRPCCompletionQueue completionQueue]
+                                       callOptions:options
+                                      disconnected:nil];
+  grpc_call_unref(call);
+  [channel unref];
+
+  // Test that we can still get the channel at this time
+  GRPCChannel *channel2 = [pool channelWithHost:kDummyHost
+                                    callOptions:options
+                                   destroyDelay:kDestroyDelay];
+  XCTAssertEqual(channel, channel2);
+  call = [channel2 unmanagedCallWithPath:@"dummy.path"
+                         completionQueue:[GRPCCompletionQueue completionQueue]
+                             callOptions:options
+                            disconnected:nil];
+
+  // Test that after the destroy delay, the channel is still alive
+  sleep(kDestroyDelay + 1);
+  XCTAssertFalse(channel.disconnected);
 }
 
-- (void)testClearChannels {
-  GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeInsecure;
-  GRPCMutableCallOptions *options2 = [[GRPCMutableCallOptions alloc] init];
-  options2.transportType = GRPCTransportTypeChttp2BoringSSL;
-  GRPCChannelConfiguration *config1 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options1];
-  GRPCChannelConfiguration *config2 =
-      [[GRPCChannelConfiguration alloc] initWithHost:kDummyHost callOptions:options2];
-  GRPCChannelPool *pool = [[GRPCChannelPool alloc] init];
-
-  GRPCChannel *channel1 = [pool channelWithConfiguration:config1];
-  GRPCChannel *channel2 = [pool channelWithConfiguration:config2];
-  XCTAssertNotEqual(channel1, channel2);
-
-  [pool removeAndCloseAllChannels];
-  GRPCChannel *channel3 = [pool channelWithConfiguration:config1];
-  GRPCChannel *channel4 = [pool channelWithConfiguration:config2];
-  XCTAssertNotEqual(channel1, channel3);
-  XCTAssertNotEqual(channel2, channel4);
+- (void)testGetChannelAfterChannelTimedDisconnection {
+  NSString *kDummyHost = @"dummy.host";
+  const NSTimeInterval kDestroyDelay = 1;
+
+  GRPCMutableCallOptions *options = [[GRPCMutableCallOptions alloc] init];
+  GRPCChannelPool *pool = [GRPCChannelPool sharedInstance];
+  GRPCChannel *channel = [pool channelWithHost:kDummyHost
+                                   callOptions:options
+                                  destroyDelay:kDestroyDelay];
+  grpc_call *call = [channel unmanagedCallWithPath:@"dummy.path"
+                                   completionQueue:[GRPCCompletionQueue completionQueue]
+                                       callOptions:options
+                                      disconnected:nil];
+  grpc_call_unref(call);
+  [channel unref];
+
+  sleep(kDestroyDelay + 1);
+
+  // Test that we get new channel to the same host and with the same callOptions
+  GRPCChannel *channel2 = [pool channelWithHost:kDummyHost
+                                    callOptions:options
+                                   destroyDelay:kDestroyDelay];
+  XCTAssertNotEqual(channel, channel2);
 }
 
 @end

src/objective-c/tests/ChannelTests/ChannelTests.m

@@ -20,6 +20,7 @@
 
 #import "../../GRPCClient/GRPCCallOptions.h"
 #import "../../GRPCClient/private/GRPCChannel.h"
+#import "../../GRPCClient/private/GRPCCompletionQueue.h"
 
 @interface ChannelTests : XCTestCase
 
@@ -31,63 +32,51 @@
   grpc_init();
 }
 
-- (void)testSameConfiguration {
-  NSString *host = @"grpc-test.sandbox.googleapis.com";
-  GRPCMutableCallOptions *options = [[GRPCMutableCallOptions alloc] init];
-  options.userAgentPrefix = @"TestUAPrefix";
-  NSMutableDictionary *args = [NSMutableDictionary new];
-  args[@"abc"] = @"xyz";
-  options.additionalChannelArgs = [args copy];
-  GRPCChannel *channel1 = [GRPCChannel channelWithHost:host callOptions:options];
-  GRPCChannel *channel2 = [GRPCChannel channelWithHost:host callOptions:options];
-  XCTAssertEqual(channel1, channel2);
-  GRPCMutableCallOptions *options2 = [options mutableCopy];
-  options2.additionalChannelArgs = [args copy];
-  GRPCChannel *channel3 = [GRPCChannel channelWithHost:host callOptions:options2];
-  XCTAssertEqual(channel1, channel3);
-}
+- (void)testTimedDisconnection {
+  NSString * const kHost = @"grpc-test.sandbox.googleapis.com";
+  const NSTimeInterval kDestroyDelay = 1;
+  GRPCCallOptions *options = [[GRPCCallOptions alloc] init];
+  GRPCChannelConfiguration *configuration = [[GRPCChannelConfiguration alloc] initWithHost:kHost callOptions:options];
+  GRPCChannel *channel = [[GRPCChannel alloc] initWithChannelConfiguration:configuration
+                                                              destroyDelay:kDestroyDelay];
+  BOOL disconnected;
+  grpc_call *call = [channel unmanagedCallWithPath:@"dummy.path"
+                                   completionQueue:[GRPCCompletionQueue completionQueue]
+                                       callOptions:options
+                                      disconnected:&disconnected];
+  XCTAssertFalse(disconnected);
+  grpc_call_unref(call);
+  [channel unref];
+  XCTAssertFalse(channel.disconnected, @"Channel is pre-maturely disconnected.");
+  sleep(kDestroyDelay + 1);
+  XCTAssertTrue(channel.disconnected, @"Channel is not disconnected after delay.");
 
-- (void)testDifferentHost {
-  NSString *host1 = @"grpc-test.sandbox.googleapis.com";
-  NSString *host2 = @"grpc-test2.sandbox.googleapis.com";
-  NSString *host3 = @"http://grpc-test.sandbox.googleapis.com";
-  NSString *host4 = @"dns://grpc-test.sandbox.googleapis.com";
-  NSString *host5 = @"grpc-test.sandbox.googleapis.com:80";
-  GRPCMutableCallOptions *options = [[GRPCMutableCallOptions alloc] init];
-  options.userAgentPrefix = @"TestUAPrefix";
-  NSMutableDictionary *args = [NSMutableDictionary new];
-  args[@"abc"] = @"xyz";
-  options.additionalChannelArgs = [args copy];
-  GRPCChannel *channel1 = [GRPCChannel channelWithHost:host1 callOptions:options];
-  GRPCChannel *channel2 = [GRPCChannel channelWithHost:host2 callOptions:options];
-  GRPCChannel *channel3 = [GRPCChannel channelWithHost:host3 callOptions:options];
-  GRPCChannel *channel4 = [GRPCChannel channelWithHost:host4 callOptions:options];
-  GRPCChannel *channel5 = [GRPCChannel channelWithHost:host5 callOptions:options];
-  XCTAssertNotEqual(channel1, channel2);
-  XCTAssertNotEqual(channel1, channel3);
-  XCTAssertNotEqual(channel1, channel4);
-  XCTAssertNotEqual(channel1, channel5);
+  // Check another call creation returns null and indicates disconnected.
+  call = [channel unmanagedCallWithPath:@"dummy.path"
+                        completionQueue:[GRPCCompletionQueue completionQueue]
+                            callOptions:options
+                           disconnected:&disconnected];
+  XCTAssert(call == NULL);
+  XCTAssertTrue(disconnected);
 }
 
-- (void)testDifferentChannelParameters {
-  NSString *host = @"grpc-test.sandbox.googleapis.com";
-  GRPCMutableCallOptions *options1 = [[GRPCMutableCallOptions alloc] init];
-  options1.transportType = GRPCTransportTypeChttp2BoringSSL;
-  NSMutableDictionary *args = [NSMutableDictionary new];
-  args[@"abc"] = @"xyz";
-  options1.additionalChannelArgs = [args copy];
-  GRPCMutableCallOptions *options2 = [[GRPCMutableCallOptions alloc] init];
-  options2.transportType = GRPCTransportTypeInsecure;
-  options2.additionalChannelArgs = [args copy];
-  GRPCMutableCallOptions *options3 = [[GRPCMutableCallOptions alloc] init];
-  options3.transportType = GRPCTransportTypeChttp2BoringSSL;
-  args[@"def"] = @"uvw";
-  options3.additionalChannelArgs = [args copy];
-  GRPCChannel *channel1 = [GRPCChannel channelWithHost:host callOptions:options1];
-  GRPCChannel *channel2 = [GRPCChannel channelWithHost:host callOptions:options2];
-  GRPCChannel *channel3 = [GRPCChannel channelWithHost:host callOptions:options3];
-  XCTAssertNotEqual(channel1, channel2);
-  XCTAssertNotEqual(channel1, channel3);
+- (void)testForceDisconnection {
+  NSString * const kHost = @"grpc-test.sandbox.googleapis.com";
+  const NSTimeInterval kDestroyDelay = 1;
+  GRPCCallOptions *options = [[GRPCCallOptions alloc] init];
+  GRPCChannelConfiguration *configuration = [[GRPCChannelConfiguration alloc] initWithHost:kHost callOptions:options];
+  GRPCChannel *channel = [[GRPCChannel alloc] initWithChannelConfiguration:configuration
+                                                              destroyDelay:kDestroyDelay];
+  grpc_call *call = [channel unmanagedCallWithPath:@"dummy.path"
+                                   completionQueue:[GRPCCompletionQueue completionQueue]
+                                       callOptions:options
+                                      disconnected:nil];
+  grpc_call_unref(call);
+  [channel disconnect];
+  XCTAssertTrue(channel.disconnected, @"Channel is not disconnected.");
+
+  // Test calling another unref here will not crash
+  [channel unref];
 }
 
 @end