Concurrency Coordination Reports

Lock Guard Coordination Report

Record one-shot guard acquisitions behind a lock and report whether a later attempt was blocked.

locked one-shot guard A coordination report can record nonblocking guard attempts. An `NSLock` wraps a critical section, and a `taken` flag started at `false` acts as an exclusive one-shot guard: the first attempt inside the lock flips the flag and is acquired, and every later attempt finds the flag already set and is reported as blocked. The lock serializes the check so the counts stay deterministic across runs. With no attempts the section is idle, with one attempt it is guarded, and a later attempt in the same run is blocked. The status line summarizes the outcome.

Lock Guard Coordination Report

attempts
lock_guard_coordination_report.swift
Replay: real traced execution (multi-file project)
import Foundation

let attempts = 1
let lock = NSLock()
var taken = false
var acquired = 0
var blocked = 0

for _ in 0..<attempts {
    lock.lock()
    if !taken {
        taken = true
        acquired += 1
    } else {
        blocked += 1
    }
    lock.unlock()
}

var status = "guarded"
if acquired == 0 {
    status = "idle"
}
if blocked > 0 {
    status = "blocked"
}

let line = "attempts=\(attempts) acquired=\(acquired) blocked=\(blocked) \(status)"

print(line)

import Foundation

let attempts = 0
let lock = NSLock()
var taken = false
var acquired = 0
var blocked = 0

for _ in 0..<attempts {
    lock.lock()
    if !taken {
        taken = true
        acquired += 1
    } else {
        blocked += 1
    }
    lock.unlock()
}

var status = "guarded"
if acquired == 0 {
    status = "idle"
}
if blocked > 0 {
    status = "blocked"
}

let line = "attempts=\(attempts) acquired=\(acquired) blocked=\(blocked) \(status)"

print(line)

import Foundation

let attempts = 2
let lock = NSLock()
var taken = false
var acquired = 0
var blocked = 0

for _ in 0..<attempts {
    lock.lock()
    if !taken {
        taken = true
        acquired += 1
    } else {
        blocked += 1
    }
    lock.unlock()
}

var status = "guarded"
if acquired == 0 {
    status = "idle"
}
if blocked > 0 {
    status = "blocked"
}

let line = "attempts=\(attempts) acquired=\(acquired) blocked=\(blocked) \(status)"

print(line)

  1. attempts ← 1, lock ← <NSLock: ⟨addr A⟩>, taken ← false, acquired ← 0

    3let attempts→ 1 = 1  //@attempts=0, 24let lock→ <NSLock: ⟨addr A⟩> = NSLock()5var taken→ false = false6var acquired→ 0 = 07var blocked→ 0 = 0

  2. for _ in 0..<attempts

    9for _ in 0..<attempts1 {10    lock<NSLock: ⟨addr A⟩>.lock()11    if !taken {

  3. if !taken

    10lock.lock()11if !takenfalse {12    taken = true13    acquired0 += 114} else {

  4. lock.unlock()

    16    }17    lock<NSLock: ⟨addr A⟩>.unlock()18}

  5. status ← guarded, line ← attempts=1 acquired=1 blocked=0 guarded

    20var status→ guarded = "guarded"21if acquired == 0 {22    status = "idle"23}24if blocked > 0 {25    status = "blocked"26}2728let line→ attempts=1 acquired=1 blocked=0 guarded = "attempts=\(attempts1) acquired=\(acquired1) blocked=\(blocked0) \(statusguarded)"2930print(lineattempts=1 acquired=1 blocked=0 guarded)
    outputattempts=1 acquired=1 blocked=0 guarded

  1. attempts ← 0, lock ← <NSLock: ⟨addr A⟩>, taken ← false, acquired ← 0

    3let attempts→ 0 = 04let lock→ <NSLock: ⟨addr A⟩> = NSLock()5var taken→ false = false6var acquired→ 0 = 07var blocked→ 0 = 089for _ in 0..<attempts {10    lock.lock()11    if !taken {12        taken = true13        acquired += 114    } else {15        blocked += 116    }17    lock.unlock()18}1920var status→ guarded = "guarded"21if acquired == 0 {

  2. if acquired == 0

    20var status = "guarded"21if acquired0 == 0 {22    status = "idle"23}

  3. line ← attempts=0 acquired=0 blocked=0 idle

    28let line→ attempts=0 acquired=0 blocked=0 idle = "attempts=\(attempts0) acquired=\(acquired0) blocked=\(blocked0) \(statusidle)"2930print(lineattempts=0 acquired=0 blocked=0 idle)
    outputattempts=0 acquired=0 blocked=0 idle

  1. attempts ← 2, lock ← <NSLock: ⟨addr A⟩>, taken ← false, acquired ← 0

    3let attempts→ 2 = 24let lock→ <NSLock: ⟨addr A⟩> = NSLock()5var taken→ false = false6var acquired→ 0 = 07var blocked→ 0 = 0

  2. for _ in 0..<attempts

    pass 1 of 2
    9for _ in 0..<attempts2 {10    lock<NSLock: ⟨addr A⟩>.lock()11    if !taken {

  3. if !taken

    10lock.lock()11if !takenfalse {12    taken = true13    acquired0 += 114} else {

  4. lock.unlock()

    16    }17    lock<NSLock: ⟨addr A⟩>.unlock()18}

  5. for _ in 0..<attempts

    pass 2 of 2
    9for _ in 0..<attempts2 {10    lock<NSLock: ⟨addr A⟩>.lock()11    if !taken {

  6. else

    13    acquired += 114} else {15    blocked0 += 116}

  7. lock.unlock()

    16    }17    lock<NSLock: ⟨addr A⟩>.unlock()18}

  8. status ← guarded

    20var status→ guarded = "guarded"21if acquired == 0 {

  9. if blocked > 0

    23}24if blocked1 > 0 {25    status = "blocked"26}

  10. line ← attempts=2 acquired=1 blocked=1 blocked

    28let line→ attempts=2 acquired=1 blocked=1 blocked = "attempts=\(attempts2) acquired=\(acquired1) blocked=\(blocked1) \(statusblocked)"2930print(lineattempts=2 acquired=1 blocked=1 blocked)
    outputattempts=2 acquired=1 blocked=1 blocked