grpc/src/objective-c/RxLibrary/GRXConcurrentWriteable.h

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#import <Foundation/Foundation.h>

#import "GRXWriter.h"
#import "GRXWriteable.h"

// This is a thread-safe wrapper over a GRXWriteable instance. It lets one enqueue calls to a
// GRXWriteable instance for the main thread, guaranteeing that writesFinishedWithError: is the last
// message sent to it (no matter what messages are sent to the wrapper, in what order, nor from
// which thread). It also guarantees that, if cancelWithError: is called from the main thread (e.g.
// by the app cancelling the writes), no further messages are sent to the writeable except
// writesFinishedWithError:.
//
// TODO(jcanizales): Let the user specify another queue for the writeable callbacks.
@interface GRXConcurrentWriteable : NSObject

// The GRXWriteable passed is the wrapped writeable.
// The GRXWriteable instance is retained until writesFinishedWithError: is sent to it, and released
// after that.
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable NS_DESIGNATED_INITIALIZER;

// Enqueues writeValue: to be sent to the writeable in the main thread.
// The passed handler is invoked from the main thread after writeValue: returns.
- (void)enqueueValue:(id)value completionHandler:(void (^)())handler;

// Enqueues writesFinishedWithError:nil to be sent to the writeable in the main thread. After that
// message is sent to the writeable, all other methods of this object are effectively noops.
- (void)enqueueSuccessfulCompletion;

// If the writeable has not yet received a writesFinishedWithError: message, this will enqueue one
// to be sent to it in the main thread, and cancel all other pending messages to the writeable
// enqueued by this object (both past and future).
// The error argument cannot be nil.
- (void)cancelWithError:(NSError *)error;

// Cancels all pending messages to the writeable enqueued by this object (both past and future).
// Because the writeable won't receive writesFinishedWithError:, this also releases the writeable.
- (void)cancelSilently;
@end