[英]Can two CloudKit call deadlock each other? How to fix?
Inside a performQuery
an other performQuery
is being called. 在performQuery
内部,正在调用另一个performQuery
。 The recordType
arguments are same for both, but the predicate
s are different. 两者的recordType
参数相同,但predicate
不同。
The second performQuery
never returns, the App just runs and waits for CloudKit to respond. 第二个performQuery
永不返回,该应用程序仅运行并等待CloudKit响应。
The pseudo code is like this: 伪代码是这样的:
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate), inZoneWithID: nil, completionHandler: {records, error in
if error == nil {
//.. problem is not name collision or reusing the same parameter, coming codepart is called though other methods
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate2), inZoneWithID: nil, completionHandler: {records, error in
//THIS LINE WILL NEVER GET REACHED
if error == nil {
} else {
println(error.localizedDescription)
}
dispatch_semaphore_signal(sema2)
})
dispatch_semaphore_wait(sema2, DISPATCH_TIME_FOREVER)
//..
} else {
println(error.localizedDescription)
}
dispatch_semaphore_signal(sema)
})
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER)
It looks like a semaphore threading issue. 看起来是信号量线程问题。 You are reusing the sama parameter. 您正在重用sama参数。 The last dispatch_semaphore_signal must be moved to above inside the else. 最后的dispatch_semaphore_signal必须移到else内部的上方。 Then the first dispatch_semaphore_wait can be removed completely. 然后,可以完全删除第一个dispatch_semaphore_wait。 So it will be like this: 因此它将是这样的:
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate), inZoneWithID: nil, completionHandler: {records, error in
if error == nil {
//.. problem is not name collision, it is nested though other blocks
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate2), inZoneWithID: nil, completionHandler: {records, error in
//THIS LINE WILL NEVER GET REACHED
if error == nil {
} else {
println(error.localizedDescription)
}
dispatch_semaphore_signal(sema)
})
//..
} else {
println(error.localizedDescription)
dispatch_semaphore_signal(sema)
}
})
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER)
Deadlock was fixed like this: Inner query moved after outer query. 死锁是这样修复的:内部查询在外部查询之后移动。 Both semaphore retained. 两种信号量均保留。 Outer completion handler is finished before inner completion handler would start. 外部完成处理程序将在内部完成处理程序启动之前完成。 From CloudKit returned records are stored in local variables. 从CloudKit返回的记录存储在局部变量中。
var records: [AnyObject]! = []
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate), inZoneWithID: nil, completionHandler: {records2, error in
if error == nil {
records = records2
} else {
println(error.localizedDescription)
}
dispatch_semaphore_signal(sema)
})
dispatch_semaphore_wait(sema, DISPATCH_TIME_FOREVER)
//HERE I can use records
var records3: [AnyObject]! = []
publicDatabase.performQuery(CKQuery(recordType: recordTypeSrc, predicate: predicate2), inZoneWithID: nil, completionHandler: {records4, error in
if error == nil {
records3 = records4
} else {
println(error.localizedDescription)
}
dispatch_semaphore_signal(sema2)
})
dispatch_semaphore_wait(sema2, DISPATCH_TIME_FOREVER)
//HERE I can use records3 too
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