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api:thread [2017/06/11 10:02] vexatos |
api:thread [2019/12/06 14:15] (current) jasonc [Thread API] |
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| The Thread API provides a variation of coroutines for openos. A thread is superior to basic coroutines in many ways and, for many workflows, is easier to work with. An openos thread is an autonomous non-blocking detachable process. | The Thread API provides a variation of coroutines for openos. A thread is superior to basic coroutines in many ways and, for many workflows, is easier to work with. An openos thread is an autonomous non-blocking detachable process. | ||
| - | * **Autonomous**: Threads asynchronously begin execution immediately after creation without needing to call resume. Unlike coroutines, threads self-resume after yielding and do not yield back to the line of code where they were created. Programming with coroutines builds on the cooperative yield and resume calls made explicitly by the user. Yielding or calling `event.pull` from a thread, however, only temporarily blocks just that thread and continue on its own. | + | * **Autonomous**: Threads asynchronously begin execution immediately after creation without needing to call resume. Unlike coroutines, threads self-resume after yielding and do not yield back to the line of code where they were created. Programming with coroutines builds on the cooperative yield and resume calls made explicitly by the user. Yielding or calling `event.pull` from a thread, however, only temporarily blocks just that thread and will continue on its own. |
| - | * **Non-Blocking**: Threads can call `computer.pullSignal` (or any higher level wrapper such as `event.pull`, `io.pull`, etc) without blocking the main kernel process nor any other thread. The thread itself is blocked until a signal or timeout occurs. The computational flow of the thread behaves just as if the same code where run in a script from the command line. Behind the scenes, the thread library is using pullSignal to swap between threads, and waking threads up when appropriate. This is very much unlike coroutines where `computer.pullSignal` blocks all other activity on the system until a signal or timeout occurs. | + | * **Non-Blocking**: Threads can call `computer.pullSignal` (or any higher level wrapper such as `event.pull`, `io.pull`, etc) without blocking the main kernel process nor any other thread. The thread itself is blocked until a signal or timeout occurs. The computational flow of the thread behaves just as if the same code were run in a script from the command line. Behind the scenes, the thread library is using pullSignal to swap between threads, and waking threads up when appropriate. This is very much unlike coroutines where `computer.pullSignal` blocks all other activity on the system until a signal or timeout occurs. |
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| * The thread is manually suspended. see `t:suspend()` | * The thread is manually suspended. see `t:suspend()` | ||
| + | ====Event Registration Independence==== | ||
| + | |||
| + | A thread maintains an independent set of event registrations; it does not inherit any and it does not share any. Any event registration made (e.g. listeners or timers) inside a thread belongs to that thread. | ||
| + | * When a thread dies all of its event registrations die with it. | ||
| + | * A `suspended` thread ignores events (see `t:status() suspended`) | ||
| + | * A thread cannot access/remove/interfere with another thread's event registrations. | ||
| + | * A pushed event is observed by all running threads on the system. | ||
| + | * Two separate threads can `event.pull` for the same event, and each thread will observe the event independently. | ||
| ===== Overview ===== | ===== Overview ===== | ||
| Line 37: | Line 45: | ||
| - `thread.create(thread_proc: function[, ...]): table` | - `thread.create(thread_proc: function[, ...]): table` | ||
| - | Starts a new thread executing the function `thread_proc` and returns its thread handle, see [[api:thread#Thread_Handle_API|Thread Handle API]]. This method takes an optional `...` which is passed to `thread_proc`. The runtime of the thread continues autonomously. | + | Starts a new thread executing the function `thread_proc` and returns its thread handle, see [[api:thread#Thread_Handle_API|Thread Handle API]]. This method takes an optional `...` which is passed to `thread_proc`. The runtime of the thread continues autonomously. |
| ```lua | ```lua | ||
| Line 60: | Line 68: | ||
| - `thread.waitForAll(threads: table[, timeout: number]): boolean, string` | - `thread.waitForAll(threads: table[, timeout: number]): boolean, string` | ||
| - | Waits for the array of `threads` to complete. This blocking call can return in `timeout` seconds if provided. Returns success and an error message on failure. A thread is "completed" under multiple conditions, see `t:join()` for details. | + | Waits for the array of `threads` to complete. This blocking call can return in `timeout` seconds if provided. Returns success and an error message on failure. A thread is "completed" under multiple conditions, see `t:join()` for details. |
| ```lua | ```lua | ||
| Line 84: | Line 92: | ||
| - `thread.waitForAny(threads: table[, timeout: number): boolean, string` | - `thread.waitForAny(threads: table[, timeout: number): boolean, string` | ||
| - | Waits for any single thread to complete and is otherwise equivalent to `thread.waitForAll()` | + | Waits for any single thread to complete and is otherwise equivalent to `thread.waitForAll()` |
| ```lua | ```lua | ||
| Line 114: | Line 122: | ||
| ``` | ``` | ||
| - | * Please note that threads resume order is not specified | + | Please note that threads resume order is not specified and this example may print "D" before it prints "Main program end" |
| + | |||
| + | - `thread.current(): table` | ||
| + | |||
| + | Returns the current thread `t` object. The init process does not represent a thread and nothing is returned from this method if called from the init process and not inside any thread. | ||
| + | |||
| ===== Thread Handle API ===== | ===== Thread Handle API ===== | ||
| Line 120: | Line 134: | ||
| - `t:resume(): boolean, string` | - `t:resume(): boolean, string` | ||
| - | Resumes (or thaws) a suspended thread. Returns success and an error message on failure. A thread begins its life already in a running state and thus basic thread workflows will not ever need to call `t:resume()`. A "running" thread will autonomously continue until it completes. `t:resume()` is only necessary to resume a thread that has been suspended(`t:suspend()`). **Note** that because you are not directly resuming the thread any exceptions thrown from the thread are absorbed by the threading library and not exposed to your process. | + | Resumes (or thaws) a suspended thread. Returns success and an error message on failure. A thread begins its life already in a running state and thus basic thread workflows will not ever need to call `t:resume()`. A "running" thread will autonomously continue until it completes. `t:resume()` is only necessary to resume a thread that has been suspended(`t:suspend()`). **Note** that because you are not directly resuming the thread any exceptions thrown from the thread are absorbed by the threading library and not exposed to your process. |
| - | * At this time there is no way to hook in an exception handler for threads but for now `event.onError` is used to print the error message to "/tmp/event.log". Please note that currently the hard interrupt exception is only thrown once, and the behavior of a process with threads when a hard interrupt is thrown is unspecified. At this time, any one of the threads or the parent process may take the exception. These details are not part of the specification for threads, any this implementation detail may change later. | + | * At this time there is no way to hook in an exception handler for threads but for now `event.onError` is used to print the error message to "/tmp/event.log". Please note that currently the hard interrupt exception is only thrown once, and the behavior of a process with threads when a hard interrupt is thrown is unspecified. At this time, any one of the threads or the parent process may take the exception. These details are not part of the specification for threads and any part of this implementation detail may change later. |
| - `t:suspend(): boolean, string` | - `t:suspend(): boolean, string` | ||
| - | Suspends (or freezes) a running thread. Returns success and an error message on failure. A "suspended" thread never autonomously wakes up and dies as soon as its parent process (if attached) closes. A suspended thread ignores events. That means any event listeners or timers created inside the thread will not respond to event notifications. Note that threads do not buffer event signals and a suspended thread may miss event signals it was waiting for. For example, if a thread was last waiting on `event.pull("modem_message")` and is "suspended" and a "modem_message" is received by the computer then the thread will miss the event and never know it happened. | + | Suspends (or freezes) a running thread. Returns success and an error message on failure. A "suspended" thread never autonomously wakes up and dies as soon as its parent process (if attached) closes. A suspended thread ignores events. That means any event listeners or timers created inside the thread will not respond to event notifications. Note that threads do not buffer event signals and a suspended thread may miss event signals it was waiting for. For example, if a thread was last waiting on `event.pull("modem_message")` and is "suspended" and a "modem_message" is received by the computer then the thread will miss the event and never know it happened. Please note that if you suspend a thread that is blocked waiting for an event, it is unspecified which event the thread will receive when it is next resumed. |
| + | |||
| + | Suspending the current thread causes the thread to immediately yield and does not resume until `t:resume()` is called explicitly elsewhere. | ||
| - | **Special notes about t:resume, t:suspend** | + | **Special notes about `t:resume`, `t:suspend`** |
| - | Do not think of these methods as `coroutine.resume()` nor `coroutine.yield()`. These methods are indirect and a thread will asynchronously start or stop running on its own. Contrast this to coroutine methods which directly and immediately invoke execution or leave execution of a coroutine. Consider this example: | + | Do not think of these methods as `coroutine.resume()` nor `coroutine.yield()`. These methods are indirect and a thread will asynchronously start or stop running on its own. Contrast this to coroutine methods which directly and immediately invoke execution or leave execution of a coroutine. Consider these examples: |
| ```lua | ```lua | ||
| Line 137: | Line 153: | ||
| t = thread.create(function() | t = thread.create(function() | ||
| print("start") | print("start") | ||
| - | t:suspend() | + | thread.current():suspend() |
| print("after suspend") | print("after suspend") | ||
| os.sleep() | os.sleep() | ||
| Line 147: | Line 163: | ||
| ``` | ``` | ||
| start | start | ||
| + | ``` | ||
| + | |||
| + | ```lua | ||
| + | local thread = require("thread") | ||
| + | local t -- this example needs an upvalue to t | ||
| + | t = thread.create(function() | ||
| + | print("start") | ||
| + | thread.current():suspend() | ||
| + | print("after suspend") | ||
| + | os.sleep() | ||
| + | print("after sleep") | ||
| + | end) | ||
| + | print("outside thread create") | ||
| + | t:resume() | ||
| + | print("after resume") | ||
| + | ``` | ||
| + | |||
| + | Output: | ||
| + | ``` | ||
| + | start | ||
| + | outside thread create | ||
| after suspend | after suspend | ||
| + | after resume | ||
| + | after sleep | ||
| ``` | ``` | ||
| - `t:kill()` | - `t:kill()` | ||
| - | Stabby stab! Kills the thread dead. The thread is terminated and will not continue its thread function. Any event registrations it made will die with it. Keep in mind that the core underlying Lua type is a coroutine which is not a preemptive thread. Thus, the thread's stopping points are deterministic, meaning that you can predict exactly where the thread will stop. Consider this example: | + | Stabby stab! Kills the thread dead. The thread is terminated and will not continue its thread function. Any event registrations it made will die with it. Keep in mind that the core underlying Lua type is a coroutine which is not a preemptive thread. Thus, the thread's stopping points are deterministic, meaning that you can predict exactly where the thread will stop. Consider this example: |
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| - `t:status(): string` | - `t:status(): string` | ||
| - | Returns the thread status as a string. | + | Returns the thread status as a string. |
| - | * **"running"** | + | * **"running"** |
| - | A running thread will continue (autonomously reactivating) after yields and blocking calls until its thread function exits. This is the default and initial state of a created thread. A thread remains in the "running" state even when blocked or not active. A running thread can be suspended(`t:suspend()`) or killed (`t:kill()`) but not resumed(`t:resume()`). A running thread will block calls to `t:join()` and block its parent from closing. Unlike a coroutine which appears "suspended" when not executing in this very moment, a thread state remains "running" even when waiting for an event. Consider this example | + | A running thread will continue (autonomously reactivating) after yields and blocking calls until its thread function exits. This is the default and initial state of a created thread. A thread remains in the "running" state even when blocked or not active. A running thread can be suspended(`t:suspend()`) or killed (`t:kill()`) but not resumed(`t:resume()`). A running thread will block calls to `t:join()` and block its parent from closing. Unlike a coroutine which appears "suspended" when not executing in this very moment, a thread state remains "running" even when waiting for an event. |
| - | * **"suspended"** | + | * **"suspended"** |
| - | A suspended threaded will remain suspended and never self resume execution of its thread function. A suspended thread is automatically killed when its attach parent closes or when you attempt to `t:join()` it. A suspended thread ignores event signals, and any event registrations made from the context of the thread, or any child threads created therein, also ignore any event signals. A suspended thread's children behave as if suspended even if their status is "running". A suspended thread can be resumed(`t:resume()`) or killed (`t:kill()`) but not suspended(`t:suspend()`). | + | A suspended thread will remain suspended and never self resume execution of its thread function. A suspended thread is automatically killed when its attached parent closes or when you attempt to `t:join()` it. A suspended thread ignores event signals, and any event registrations made from the context of the thread, or any child threads created therein, also ignore any event signals. A suspended thread's children behave as if suspended even if their status is "running". A suspended thread can be resumed(`t:resume()`) or killed (`t:kill()`) but not suspended(`t:suspend()`). |
| - | * **"dead"** | + | * **"dead"** |
| - | A dead thread has completed or aborted its execution or has been terminated. It cannot be resumed(`t:resume()`) nor suspended(`t:suspend()`). A dead thread does not block a parent process from closing. Killing a dead thread is not an error but does nothing. | + | A dead thread has completed or aborted its execution or has been terminated. It cannot be resumed(`t:resume()`) nor suspended(`t:suspend()`). A dead thread does not block a parent process from closing. Killing a dead thread is not an error but does nothing. |
| ** Status Examples ** | ** Status Examples ** | ||
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| - `t:attach([level: number]): boolean, string` | - `t:attach([level: number]): boolean, string` | ||
| - | Attaches a thread to a process, conventionally known as a child thread or attached thread. `level` is an optional used to get parent processes, 0 or nil uses the currently running process. When initially created a thread is already attached to the current process. This method returns nil and an error message if `level` refers to a nonexistent process, otherwise it returns truthy. | + | Attaches a thread to a process, conventionally known as a child thread or attached thread. `level` is an optional used to get parent processes, 0 or nil uses the currently running process. When initially created a thread is already attached to the current process. This method returns nil and an error message if `level` refers to a nonexistent process, otherwise it returns truthy. An attached thread blocks its parent process from closing until the thread dies (or is killed, or the parent process aborts). |
| - | - `t:detach()` | + | - `t:detach(): table, string` |
| - | Detaches a thread from its parent if it has one. Returns nil and an error message if no action was taken, otherwise returns self (handy if you want to create and detach a thread in one line). | + | Detaches a thread from its parent if it has one. Returns nil and an error message if no action was taken, otherwise returns self (handy if you want to create and detach a thread in one line). A detached thread will continue to run until the computer is shutdown or rebooted, or the thread dies. |
| ```lua | ```lua | ||
| Line 253: | Line 292: | ||
| - `t:join([timeout: number]): boolean, string` | - `t:join([timeout: number]): boolean, string` | ||
| - | Blocks the caller until `t` is no longer running or (optionally) returns false if `timeout` seconds is reached. After a call to `t:join()` the thread state is "dead". Any of the following circumstances allow `join` to finish and unblock the caller | + | Blocks the caller until `t` is no longer running or (optionally) returns false if `timeout` seconds is reached. After a call to `t:join()` the thread state is "dead". Any of the following circumstances allow `join` to finish and unblock the caller |
| - | * The thread continues running until it returns from its thread function | + | * The thread continues running until it returns from its thread function |
| - | * The thread aborts, or throws an uncaught exception | + | * The thread aborts, or throws an uncaught exception |
| - | * The thread is suspended | + | * The thread is suspended |
| - | * The thread is killed | + | * The thread is killed |
| - | Calling `thread.waitForAll({t})` is functionally equivalent to calling `t:join()`. When a processs is closing it will call `thread.waitForAll` on the group of its child threads if it has any. A child thread blocks its parent thread by the same machanism. | + | Calling `thread.waitForAll({t})` is functionally equivalent to calling `t:join()`. When a processs is closing it will call `thread.waitForAll` on the group of its child threads if it has any. A child thread blocks its parent thread by the same machanism. |
| ===== Thread Exception Example ===== | ===== Thread Exception Example ===== | ||
| Line 276: | Line 315: | ||
| print("reader done") | print("reader done") | ||
| end) | end) | ||
| - | print("p end", t:status()) | + | print("p end", reader:status()) |
| ``` | ``` | ||
| Line 324: | Line 363: | ||
| ```lua | ```lua | ||
| + | local event = require("event") | ||
| local thread = require("thread") | local thread = require("thread") | ||
| thread.create(function() | thread.create(function() | ||