DispatchQueue の多重度

DispatchQueue の多重度を調べてみたところ、64個であることがわかった。

【2018/08/31 0:00 訂正】以前50と書いていたが、数え間違えていた…(´・ω・｀)

確認コード

let semaphore = DispatchSemaphore(value: 0)
for id in 1..<100 {
  DispatchQueue.global(qos: .default).async {
    Thread.sleep(forTimeInterval: 0.5)
    NSLog("id: \(id)")
    guard id == 99 {
      return
    }
    semaphore.signal()
  }
}
semaphore.wait()

結果

2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642945] id: 46
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642912] id: 13
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642920] id: 21
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642935] id: 36
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642943] id: 44
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642915] id: 16
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642906] id: 7
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642950] id: 51
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642952] id: 53
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642937] id: 38
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642938] id: 39
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642911] id: 12
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642913] id: 14
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642903] id: 4
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642900] id: 1
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642948] id: 49
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642933] id: 34
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642921] id: 22
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642918] id: 19
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642909] id: 10
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642901] id: 2
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642939] id: 40
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642910] id: 11
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642907] id: 8
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642941] id: 42
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642955] id: 56
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642908] id: 9
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642954] id: 55
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642947] id: 48
2018-08-29 23:09:36.512 HTTP-CLIENT[79197:7642924] id: 25
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642961] id: 62
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642917] id: 18
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642926] id: 27
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642922] id: 23
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642957] id: 58
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642932] id: 33
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642960] id: 61
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642931] id: 32
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642925] id: 26
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642928] id: 29
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642944] id: 45
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642927] id: 28
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642936] id: 37
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642959] id: 60
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642905] id: 6
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642958] id: 59
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642916] id: 17
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642949] id: 50
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642934] id: 35
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642963] id: 64
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642951] id: 52
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642956] id: 57
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642942] id: 43
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642914] id: 15
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642946] id: 47
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642962] id: 63
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642902] id: 3
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642940] id: 41
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642953] id: 54
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642919] id: 20
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642923] id: 24
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642904] id: 5
2018-08-29 23:09:36.513 HTTP-CLIENT[79197:7642929] id: 30
2018-08-29 23:09:36.514 HTTP-CLIENT[79197:7642930] id: 31
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642943] id: 69
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642945] id: 65
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642915] id: 70
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642935] id: 68
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642912] id: 66
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642920] id: 67
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642906] id: 71
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642950] id: 72
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642952] id: 73
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642937] id: 74
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642911] id: 76
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642948] id: 80
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642913] id: 77
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642903] id: 78
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642909] id: 84
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642900] id: 79
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642938] id: 75
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642918] id: 83
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642901] id: 85
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642921] id: 82
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642933] id: 81
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642939] id: 86
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642910] id: 87
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642941] id: 89
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642907] id: 88
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642955] id: 90
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642908] id: 91
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642954] id: 92
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642961] id: 95
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642924] id: 94
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642947] id: 93
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642926] id: 97
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642917] id: 96
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642922] id: 98
2018-08-29 23:09:37.017 HTTP-CLIENT[79197:7642957] id: 99