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Add an optional target queue to for database operations #801

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Add an optional target queue to for database operations #801

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3fdec83
Add an optional target queue to for database operations
sharplet Apr 21, 2018
05cd7cc
Merge branch 'master' into target-queue
jberkel Dec 19, 2018
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31 changes: 24 additions & 7 deletions Sources/SQLite/Core/Connection.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -101,11 +101,21 @@ public final class Connection {
///
/// Default: `false`.
///
/// - target: An optional target queue for database operations to be executed on.
/// Set this to a custom serial queue if you need to schedule work that must be
/// synchronized with respect to database operations.
///
/// **Important:** The target queue **must not** be a concurrent queue, or access
/// to the returned connection is no longer guaranteed be thread-safe.
///
/// - Throws: `Result.Error` iff a connection cannot be established.
///
/// - Returns: A new database connection.
public init(_ location: Location = .inMemory, readonly: Bool = false) throws {
public init(_ location: Location = .inMemory, readonly: Bool = false, target: DispatchQueue? = nil) throws {
queue = DispatchQueue(label: "SQLite.Database", target: target)
let flags = readonly ? SQLITE_OPEN_READONLY : SQLITE_OPEN_CREATE | SQLITE_OPEN_READWRITE
try check(sqlite3_open_v2(location.description, &_handle, flags | SQLITE_OPEN_FULLMUTEX, nil))
queue.setSpecific(key: Connection.queueKey, value: queueContext)
(target ?? queue).setSpecific(key: queueKey, value: queueContext)
}

/// Initializes a new connection to a database.
Expand All @@ -119,11 +129,18 @@ public final class Connection {
///
/// Default: `false`.
///
/// - target: An optional target queue for database operations to be executed on.
/// Set this to a custom serial queue if you need to schedule work that must be
/// synchronized with respect to database operations.
///
/// **Important:** The target queue **must not** be a concurrent queue, or access
/// to the returned connection is no longer guaranteed be thread-safe.
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could this be asserted in code?

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That would be nice! Currently I'm not aware of public API to check whether a queue is serial or concurrent. 🤔

///
/// - Throws: `Result.Error` iff a connection cannot be established.
///
/// - Returns: A new database connection.
public convenience init(_ filename: String, readonly: Bool = false) throws {
try self.init(.uri(filename), readonly: readonly)
public convenience init(_ filename: String, readonly: Bool = false, target: DispatchQueue? = nil) throws {
try self.init(.uri(filename), readonly: readonly, target: target)
}

deinit {
Expand Down Expand Up @@ -631,7 +648,7 @@ public final class Connection {
// MARK: - Error Handling

func sync<T>(_ block: () throws -> T) rethrows -> T {
if DispatchQueue.getSpecific(key: Connection.queueKey) == queueContext {
if DispatchQueue.getSpecific(key: queueKey) == queueContext {
return try block()
} else {
return try queue.sync(execute: block)
Expand All @@ -646,9 +663,9 @@ public final class Connection {
throw error
}

fileprivate var queue = DispatchQueue(label: "SQLite.Database", attributes: [])
fileprivate var queue: DispatchQueue

fileprivate static let queueKey = DispatchSpecificKey<Int>()
fileprivate let queueKey = DispatchSpecificKey<Int>()

fileprivate lazy var queueContext: Int = unsafeBitCast(self, to: Int.self)

Expand Down