Mutex for Kotlin/Common #508
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| Original file line number | Diff line number | Diff line change | ||||
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| @@ -0,0 +1,89 @@ | ||||||
| package kotlinx.atomicfu.locks | ||||||
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| import kotlin.contracts.ExperimentalContracts | ||||||
| import kotlin.contracts.InvocationKind | ||||||
| import kotlin.contracts.contract | ||||||
| import kotlin.time.Duration | ||||||
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| /** | ||||||
| * Mutual exclusion for Kotlin Multiplatform. | ||||||
| * | ||||||
| * It can protect a shared resource or critical section from multiple thread accesses. | ||||||
| * Threads can acquire the lock by calling [lock] and release the lock by calling [unlock]. | ||||||
| * | ||||||
| * When a thread calls [lock] while another thread is locked, it will suspend until the lock is released. | ||||||
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Suggested change
There is an unfortunate clash of terminology: |
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| * When multiple threads are waiting for the lock, they will acquire it in a fair order (first in first out). | ||||||
| * On JVM, a [lock] call can skip the queue if it happens in between a thread releasing and the first in queue acquiring. | ||||||
| * | ||||||
| * It is reentrant, meaning the lock holding thread can call [lock] multiple times without suspending. | ||||||
| * To release the lock (after multiple [lock] calls) an equal number of [unlock] calls are required. | ||||||
| * | ||||||
| * This Mutex should not be used in combination with coroutines and `suspend` functions | ||||||
| * as it blocks the waiting thread. | ||||||
| * Use the `Mutex` from the coroutines library instead. | ||||||
| * | ||||||
| * ```Kotlin | ||||||
| * mutex.withLock { | ||||||
| * // Critical section only executed by | ||||||
| * // one thread at a time. | ||||||
| * } | ||||||
| * ``` | ||||||
| */ | ||||||
| public expect class SynchronousMutex() { | ||||||
| /** | ||||||
| * Tries to lock this mutex, returning `false` if this mutex is already locked. | ||||||
| * | ||||||
| * It is recommended to use [withLock] for safety reasons, so that the acquired lock is always | ||||||
| * released at the end of your critical section, and [unlock] is never invoked before a successful | ||||||
| * lock acquisition. | ||||||
| * | ||||||
| * (JVM only) this call can potentially skip line. | ||||||
| */ | ||||||
| public fun tryLock(): Boolean | ||||||
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| /** | ||||||
| * Tries to lock this mutex within the given [timeout] period, | ||||||
| * returning `false` if the duration passed without locking. | ||||||
| * | ||||||
| * Note: when [tryLock] succeeds the lock needs to be released by [unlock]. | ||||||
| * When [tryLock] does not succeed the lock does not have to be released. | ||||||
| * | ||||||
| * (JVM only) throws Interrupted exception when thread is interrupted while waiting for lock. | ||||||
| */ | ||||||
| public fun tryLock(timeout: Duration): Boolean | ||||||
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| /** | ||||||
| * Locks the mutex, suspends the thread until the lock is acquired. | ||||||
| * | ||||||
| * It is recommended to use [withLock] for safety reasons, so that the acquired lock is always | ||||||
| * released at the end of your critical section, and [unlock] is never invoked before a successful | ||||||
| * lock acquisition. | ||||||
| */ | ||||||
| public fun lock() | ||||||
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| /** | ||||||
| * Releases the lock. | ||||||
| * Throws [IllegalStateException] when the current thread is not holding the lock. | ||||||
| * | ||||||
| * It is recommended to use [withLock] for safety reasons, so that the acquired lock is always | ||||||
| * released at the end of the critical section, and [unlock] is never invoked before a successful | ||||||
| * lock acquisition. | ||||||
| */ | ||||||
| public fun unlock() | ||||||
| } | ||||||
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| /** | ||||||
| * Executes the given code [block] under this mutex's lock. | ||||||
| * | ||||||
| * @return result of [block] | ||||||
| */ | ||||||
| @OptIn(ExperimentalContracts::class) | ||||||
| public inline fun <T> SynchronousMutex.withLock(block: () -> T): T { | ||||||
| contract { callsInPlace(block, InvocationKind.EXACTLY_ONCE) } | ||||||
| lock() | ||||||
| return try { | ||||||
| block() | ||||||
| } finally { | ||||||
| unlock() | ||||||
| } | ||||||
| } | ||||||
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I assume removing this implementation detail is safe, but cc @fzhinkin: he probably knows if this was already used by someone else.