1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
|
/*
*
* Copyright 2015, Google Inc.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
*/
#import "GRPCDelegateWrapper.h"
#import <gRPC/GRXWriteable.h>
@interface GRPCDelegateWrapper ()
// These are atomic so that cancellation can nillify them from any thread.
@property(atomic, strong) id<GRXWriteable> writeable;
@property(atomic, strong) id<GRXWriter> writer;
@end
@implementation GRPCDelegateWrapper {
dispatch_queue_t _writeableQueue;
// This ensures that writesFinishedWithError: is only sent once to the writeable.
dispatch_once_t _alreadyFinished;
}
- (instancetype)init {
return [self initWithWriteable:nil writer:nil];
}
// Designated initializer
- (instancetype)initWithWriteable:(id<GRXWriteable>)writeable writer:(id<GRXWriter>)writer {
if (self = [super init]) {
_writeableQueue = dispatch_get_main_queue();
_writeable = writeable;
_writer = writer;
}
return self;
}
- (void)enqueueMessage:(NSData *)message completionHandler:(void (^)())handler {
dispatch_async(_writeableQueue, ^{
// We're racing a possible cancellation performed by another thread. To turn
// all already-enqueued messages into noops, cancellation nillifies the
// writeable property. If we get it before it's nil, we won
// the race.
id<GRXWriteable> writeable = self.writeable;
if (writeable) {
[writeable writeValue:message];
handler();
}
});
}
- (void)enqueueSuccessfulCompletion {
dispatch_async(_writeableQueue, ^{
dispatch_once(&_alreadyFinished, ^{
// Cancellation is now impossible. None of the other three blocks can run
// concurrently with this one.
[self.writeable writesFinishedWithError:nil];
// Break the retain cycle with writer, and skip any possible message to the
// wrapped writeable enqueued after this one.
self.writeable = nil;
self.writer = nil;
});
});
}
- (void)cancelWithError:(NSError *)error {
NSAssert(error, @"For a successful completion, use enqueueSuccessfulCompletion.");
dispatch_once(&_alreadyFinished, ^{
// Skip any of the still-enqueued messages to the wrapped writeable. We use
// the atomic setter to nillify writer and writeable because we might be
// running concurrently with the blocks in _writeableQueue, and assignment
// with ARC isn't atomic.
id<GRXWriteable> writeable = self.writeable;
self.writeable = nil;
dispatch_async(_writeableQueue, ^{
[writeable writesFinishedWithError:error];
// Break the retain cycle with writer.
self.writer = nil;
});
});
}
- (void)cancelSilently {
dispatch_once(&_alreadyFinished, ^{
// Skip any of the still-enqueued messages to the wrapped writeable. We use
// the atomic setter to nillify writer and writeable because we might be
// running concurrently with the blocks in _writeableQueue, and assignment
// with ARC isn't atomic.
self.writeable = nil;
self.writer = nil;
});
}
@end
|
