Adding FileLock (#361)

* Issue #142 Implement non-blocking file lock

* Add lock in uninstall

* Use atomic create for lock

* Adding FileLock Tests

Author: roulpriya

.unacceptablelanguageignore

@@ -0,0 +1 @@
+Sources/SwiftlyCore/ProcessInfo.swift

Sources/Swiftly/Install.swift

@@ -81,6 +81,10 @@ struct Install: SwiftlyCommand {
         try await self.run(Swiftly.createDefaultContext())
     }
 
+    private func swiftlyHomeDir(_ ctx: SwiftlyCoreContext) -> FilePath {
+        Swiftly.currentPlatform.swiftlyHomeDir(ctx)
+    }
+
     mutating func run(_ ctx: SwiftlyCoreContext) async throws {
         let versionUpdateReminder = try await validateSwiftly(ctx)
         defer {
@@ -346,33 +350,51 @@ struct Install: SwiftlyCommand {
                 )
             }
 
-            try await Swiftly.currentPlatform.install(ctx, from: tmpFile, version: version, verbose: verbose)
+            let lockFile = Swiftly.currentPlatform.swiftlyHomeDir(ctx) / "swiftly.lock"
+            if verbose {
+                await ctx.print("Attempting to acquire installation lock at \(lockFile) ...")
+            }
 
-            let pathChanged = try await Self.setupProxies(
-                ctx,
-                version: version,
-                verbose: verbose,
-                assumeYes: assumeYes
-            )
+            let (pathChanged, newConfig) = try await withLock(lockFile) {
+                if verbose {
+                    await ctx.print("Acquired installation lock")
+                }
 
-            config.installedToolchains.insert(version)
+                var config = try await Config.load(ctx)
 
-            try config.save(ctx)
+                try await Swiftly.currentPlatform.install(
+                    ctx, from: tmpFile,
+                    version: version,
+                    verbose: verbose
+                )
 
-            // If this is the first installed toolchain, mark it as in-use regardless of whether the
-            // --use argument was provided.
-            if useInstalledToolchain {
-                try await Use.execute(ctx, version, globalDefault: false, &config)
-            }
+                let pathChanged = try await Self.setupProxies(
+                    ctx,
+                    version: version,
+                    verbose: verbose,
+                    assumeYes: assumeYes
+                )
+
+                config.installedToolchains.insert(version)
 
-            // We always update the global default toolchain if there is none set. This could
-            //  be the only toolchain that is installed, which makes it the only choice.
-            if config.inUse == nil {
-                config.inUse = version
                 try config.save(ctx)
-                await ctx.print("The global default toolchain has been set to `\(version)`")
-            }
 
+                // If this is the first installed toolchain, mark it as in-use regardless of whether the
+                // --use argument was provided.
+                if useInstalledToolchain {
+                    try await Use.execute(ctx, version, globalDefault: false, &config)
+                }
+
+                // We always update the global default toolchain if there is none set. This could
+                //  be the only toolchain that is installed, which makes it the only choice.
+                if config.inUse == nil {
+                    config.inUse = version
+                    try config.save(ctx)
+                    await ctx.print("The global default toolchain has been set to `\(version)`")
+                }
+                return (pathChanged, config)
+            }
+            config = newConfig
             await ctx.print("\(version) installed successfully!")
             return (postInstallScript, pathChanged)
         }

Sources/Swiftly/Uninstall.swift

@@ -128,16 +128,28 @@ struct Uninstall: SwiftlyCommand {
         await ctx.print("\(toolchains.count) toolchain(s) successfully uninstalled")
     }
 
-    static func execute(_ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ config: inout Config, verbose: Bool) async throws {
+    static func execute(
+        _ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ config: inout Config,
+        verbose: Bool
+    ) async throws {
         await ctx.print("Uninstalling \(toolchain)... ", terminator: "")
-        config.installedToolchains.remove(toolchain)
-        // This is here to prevent the inUse from referencing a toolchain that is not installed
-        if config.inUse == toolchain {
-            config.inUse = nil
+        let lockFile = Swiftly.currentPlatform.swiftlyHomeDir(ctx) / "swiftly.lock"
+        if verbose {
+            await ctx.print("Attempting to acquire installation lock at \(lockFile) ...")
         }
-        try config.save(ctx)
 
-        try await Swiftly.currentPlatform.uninstall(ctx, toolchain, verbose: verbose)
+        config = try await withLock(lockFile) {
+            var config = try await Config.load(ctx)
+            config.installedToolchains.remove(toolchain)
+            // This is here to prevent the inUse from referencing a toolchain that is not installed
+            if config.inUse == toolchain {
+                config.inUse = nil
+            }
+            try config.save(ctx)
+
+            try await Swiftly.currentPlatform.uninstall(ctx, toolchain, verbose: verbose)
+            return config
+        }
         await ctx.print("done")
     }
 }

Sources/SwiftlyCore/FileLock.swift

@@ -0,0 +1,108 @@
+import Foundation
+import SystemPackage
+
+enum FileLockError: Error, LocalizedError {
+    case cannotAcquireLock(FilePath)
+    case lockedByPID(FilePath, String)
+
+    var errorDescription: String? {
+        switch self {
+        case let .cannotAcquireLock(path):
+            return "Cannot acquire lock at \(path). Another process may be holding the lock. If you are sure no other processes are running, you can manually remove the lock file at \(path)."
+        case let .lockedByPID(path, pid):
+            return
+                "Lock at \(path) is held by process ID \(pid). Wait for the process to complete or manually remove the lock file if the process is no longer running."
+        }
+    }
+}
+
+/// A non-blocking file lock implementation using file creation as locking mechanism.
+/// Use case: When installing multiple Swiftly instances on the same machine,
+/// one should acquire the lock while others poll until it becomes available.
+public struct FileLock {
+    let filePath: FilePath
+
+    public static let defaultPollingInterval: TimeInterval = 1
+    public static let defaultTimeout: TimeInterval = 300.0
+
+    public init(at path: FilePath) throws {
+        self.filePath = path
+        do {
+            let fileURL = URL(fileURLWithPath: self.filePath.string)
+            let contents = Foundation.ProcessInfo.processInfo.processIdentifier.description.data(using: .utf8)
+                ?? Data()
+            try contents.write(to: fileURL, options: .withoutOverwriting)
+        } catch CocoaError.fileWriteFileExists {
+            // Read the PID from the existing lock file
+            let fileURL = URL(fileURLWithPath: self.filePath.string)
+            if let data = try? Data(contentsOf: fileURL),
+               let pidString = String(data: data, encoding: .utf8)?.trimmingCharacters(
+                   in: .whitespacesAndNewlines),
+               !pidString.isEmpty
+            {
+                throw FileLockError.lockedByPID(self.filePath, pidString)
+            } else {
+                throw FileLockError.cannotAcquireLock(self.filePath)
+            }
+        }
+    }
+
+    public static func waitForLock(
+        _ path: FilePath,
+        timeout: TimeInterval = FileLock.defaultTimeout,
+        pollingInterval: TimeInterval = FileLock.defaultPollingInterval
+    ) async throws -> FileLock {
+        let start = Date()
+        var lastError: Error?
+
+        while Date().timeIntervalSince(start) < timeout {
+            let result = Result { try FileLock(at: path) }
+
+            switch result {
+            case let .success(lock):
+                return lock
+            case let .failure(error):
+                lastError = error
+                try? await Task.sleep(for: .seconds(pollingInterval) + .milliseconds(Int.random(in: 0...200)))
+            }
+        }
+
+        // Timeout reached, throw the last error from the loop
+        if let lastError = lastError {
+            throw lastError
+        } else {
+            throw FileLockError.cannotAcquireLock(path)
+        }
+    }
+
+    public func unlock() async throws {
+        try await FileSystem.remove(atPath: self.filePath)
+    }
+}
+
+public func withLock<T>(
+    _ lockFile: FilePath,
+    timeout: TimeInterval = FileLock.defaultTimeout,
+    pollingInterval: TimeInterval = FileLock.defaultPollingInterval,
+    action: @escaping () async throws -> T
+) async throws -> T {
+    let lock: FileLock
+    do {
+        lock = try await FileLock.waitForLock(
+            lockFile,
+            timeout: timeout,
+            pollingInterval: pollingInterval
+        )
+    } catch {
+        throw SwiftlyError(message: "Failed to acquire file lock at \(lockFile): \(error.localizedDescription)")
+    }
+
+    do {
+        let result = try await action()
+        try await lock.unlock()
+        return result
+    } catch {
+        try await lock.unlock()
+        throw error
+    }
+}

Sources/SwiftlyCore/ProcessInfo.swift

@@ -0,0 +1,55 @@
+import Foundation
+
+#if os(Windows)
+import WinSDK
+#endif
+
+enum ProcessCheckError: Error {
+    case invalidPID
+    case checkFailed
+}
+
+/// Checks if a process is still running by process ID
+/// - Parameter pidString: The process ID
+/// - Returns: true if the process is running, false if it's not running or doesn't exist
+/// - Throws: ProcessCheckError if the check fails or PID is invalid
+public func isProcessRunning(pidString: String) throws -> Bool {
+    guard let pid = Int32(pidString.trimmingCharacters(in: .whitespaces)) else {
+        throw ProcessCheckError.invalidPID
+    }
+
+    return try isProcessRunning(pid: pid)
+}
+
+public func isProcessRunning(pid: Int32) throws -> Bool {
+#if os(macOS) || os(Linux)
+    let result = kill(pid, 0)
+    if result == 0 {
+        return true
+    } else if errno == ESRCH { // No such process
+        return false
+    } else if errno == EPERM { // Operation not permitted, but process exists
+        return true
+    } else {
+        throw ProcessCheckError.checkFailed
+    }
+
+#elseif os(Windows)
+    // On Windows, use OpenProcess to check if process exists
+    let handle = OpenProcess(DWORD(PROCESS_QUERY_LIMITED_INFORMATION), false, DWORD(pid))
+    if handle != nil {
+        CloseHandle(handle)
+        return true
+    } else {
+        let error = GetLastError()
+        if error == ERROR_INVALID_PARAMETER || error == ERROR_NOT_FOUND {
+            return false // Process not found
+        } else {
+            throw ProcessCheckError.checkFailed
+        }
+    }
+
+#else
+    #error("Platform is not supported")
+#endif
+}