diff options
author | Samuel Williams <samuel.williams@oriontransfer.co.nz> | 2022-10-15 21:43:45 +1300 |
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committer | GitHub <noreply@github.com> | 2022-10-15 21:43:45 +1300 |
commit | 7fcad1fa03c21b9a9916a12b816ec886a5b68920 (patch) | |
tree | fa7869c6f7b8e642258b68907506b20489df411e /scheduler.c | |
parent | 52fcb3a72446189448e96a465d8c91c469ac0ed2 (diff) |
Update `Fiber::Scheduler` documentation. (#6562)
Notes
Notes:
Merged-By: ioquatix <samuel@codeotaku.com>
Diffstat (limited to 'scheduler.c')
-rw-r--r-- | scheduler.c | 310 |
1 files changed, 309 insertions, 1 deletions
diff --git a/scheduler.c b/scheduler.c index 09fc921c88..611182741c 100644 --- a/scheduler.c +++ b/scheduler.c @@ -33,6 +33,58 @@ static ID id_io_close; static ID id_address_resolve; +static ID id_fiber_schedule; + +/* + * Document-class: Fiber::Scheduler + * + * This is not an existing class, but documentation of the interface that Scheduler + * object should comply to in order to be used as argument to Fiber.scheduler and handle non-blocking + * fibers. See also the "Non-blocking fibers" section in Fiber class docs for explanations + * of some concepts. + * + * Scheduler's behavior and usage are expected to be as follows: + * + * * When the execution in the non-blocking Fiber reaches some blocking operation (like + * sleep, wait for a process, or a non-ready I/O), it calls some of the scheduler's + * hook methods, listed below. + * * Scheduler somehow registers what the current fiber is waiting on, and yields control + * to other fibers with Fiber.yield (so the fiber would be suspended while expecting its + * wait to end, and other fibers in the same thread can perform) + * * At the end of the current thread execution, the scheduler's method #scheduler_close is called + * * The scheduler runs into a wait loop, checking all the blocked fibers (which it has + * registered on hook calls) and resuming them when the awaited resource is ready + * (e.g. I/O ready or sleep time elapsed). + * + * This way concurrent execution will be achieved transparently for every + * individual Fiber's code. + * + * Scheduler implementations are provided by gems, like + * Async[https://github.com/socketry/async]. + * + * Hook methods are: + * + * * #io_wait, #io_read, #io_write, #io_pread, #io_pwrite, and #io_select, #io_close + * * #process_wait + * * #kernel_sleep + * * #timeout_after + * * #address_resolve + * * #block and #unblock + * * (the list is expanded as Ruby developers make more methods having non-blocking calls) + * + * When not specified otherwise, the hook implementations are mandatory: if they are not + * implemented, the methods trying to call hook will fail. To provide backward compatibility, + * in the future hooks will be optional (if they are not implemented, due to the scheduler + * being created for the older Ruby version, the code which needs this hook will not fail, + * and will just behave in a blocking fashion). + * + * It is also strongly recommended that the scheduler implements the #fiber method, which is + * delegated to by Fiber.schedule. + * + * Sample _toy_ implementation of the scheduler can be found in Ruby's code, in + * <tt>test/fiber/scheduler.rb</tt> + * + */ void Init_Fiber_Scheduler(void) { @@ -56,6 +108,23 @@ Init_Fiber_Scheduler(void) id_io_close = rb_intern_const("io_close"); id_address_resolve = rb_intern_const("address_resolve"); + + id_fiber_schedule = rb_intern_const("fiber"); + +#if 0 /* for RDoc */ + rb_cFiberScheduler = rb_define_class_under(rb_cFiber, "Scheduler", rb_cObject); + rb_define_method(rb_cFiberScheduler, "close", rb_fiber_scheduler_close, 0); + rb_define_method(rb_cFiberScheduler, "process_wait", rb_fiber_scheduler_process_wait, 2); + rb_define_method(rb_cFiberScheduler, "io_wait", rb_fiber_scheduler_io_wait, 3); + rb_define_method(rb_cFiberScheduler, "io_read", rb_fiber_scheduler_io_read, 4); + rb_define_method(rb_cFiberScheduler, "io_write", rb_fiber_scheduler_io_write, 4); + rb_define_method(rb_cFiberScheduler, "kernel_sleep", rb_fiber_scheduler_kernel_sleep, 1); + rb_define_method(rb_cFiberScheduler, "address_resolve", rb_fiber_scheduler_address_resolve, 1); + rb_define_method(rb_cFiberScheduler, "timeout_after", rb_fiber_scheduler_timeout_after, 3); + rb_define_method(rb_cFiberScheduler, "block", rb_fiber_scheduler_block, 2); + rb_define_method(rb_cFiberScheduler, "unblock", rb_fiber_scheduler_unblock, 2); + rb_define_method(rb_cFiberScheduler, "fiber", rb_fiber_scheduler, -2); +#endif } VALUE @@ -101,7 +170,10 @@ rb_fiber_scheduler_set(VALUE scheduler) verify_interface(scheduler); } - // We invoke Scheduler#close when setting it to something else, to ensure the previous scheduler runs to completion before changing the scheduler. That way, we do not need to consider interactions, e.g., of a Fiber from the previous scheduler with the new scheduler. + // We invoke Scheduler#close when setting it to something else, to ensure + // the previous scheduler runs to completion before changing the scheduler. + // That way, we do not need to consider interactions, e.g., of a Fiber from + // the previous scheduler with the new scheduler. if (thread->scheduler != Qnil) { rb_fiber_scheduler_close(thread->scheduler); } @@ -135,6 +207,16 @@ VALUE rb_fiber_scheduler_current_for_thread(VALUE thread) return rb_fiber_scheduler_current_for_threadptr(rb_thread_ptr(thread)); } +/* + * + * Document-method: Fiber::Scheduler#close + * + * Called when the current thread exits. The scheduler is expected to implement this + * method in order to allow all waiting fibers to finalize their execution. + * + * The suggested pattern is to implement the main event loop in the #close method. + * + */ VALUE rb_fiber_scheduler_close(VALUE scheduler) { @@ -142,6 +224,12 @@ rb_fiber_scheduler_close(VALUE scheduler) VALUE result; + // The reason for calling `scheduler_close` before calling `close` is for + // legacy schedulers which implement `close` and expect the user to call + // it. Subsequently, that method would call `Fiber.set_scheduler(nil)` + // which should call `scheduler_close`. If it were to call `close`, it + // would create an infinite loop. + result = rb_check_funcall(scheduler, id_scheduler_close, 0, NULL); if (result != Qundef) return result; @@ -161,6 +249,17 @@ rb_fiber_scheduler_make_timeout(struct timeval *timeout) return Qnil; } +/* + * Document-method: Fiber::Scheduler#kernel_sleep + * call-seq: kernel_sleep(duration = nil) + * + * Invoked by Kernel#sleep and Mutex#sleep and is expected to provide + * an implementation of sleeping in a non-blocking way. Implementation might + * register the current fiber in some list of "which fiber wait until what + * moment", call Fiber.yield to pass control, and then in #close resume + * the fibers whose wait period has elapsed. + * + */ VALUE rb_fiber_scheduler_kernel_sleep(VALUE scheduler, VALUE timeout) { @@ -174,6 +273,34 @@ rb_fiber_scheduler_kernel_sleepv(VALUE scheduler, int argc, VALUE * argv) } #if 0 +/* + * Document-method: Fiber::Scheduler#timeout_after + * call-seq: timeout_after(duration, exception_class, *exception_arguments, &block) -> result of block + * + * Invoked by Timeout.timeout to execute the given +block+ within the given + * +duration+. It can also be invoked directly by the scheduler or user code. + * + * Attempt to limit the execution time of a given +block+ to the given + * +duration+ if possible. When a non-blocking operation causes the +block+'s + * execution time to exceed the specified +duration+, that non-blocking + * operation should be interrupted by raising the specified +exception_class+ + * constructed with the given +exception_arguments+. + * + * General execution timeouts are often considered risky. This implementation + * will only interrupt non-blocking operations. This is by design because it's + * expected that non-blocking operations can fail for a variety of + * unpredictable reasons, so applications should already be robust in handling + * these conditions and by implication timeouts. + * + * However, as a result of this design, if the +block+ does not invoke any + * non-blocking operations, it will be impossible to interrupt it. If you + * desire to provide predictable points for timeouts, consider adding + * +sleep(0)+. + * + * If the block is executed successfully, its result will be returned. + * + * The exception will typically be raised using Fiber#raise. + */ VALUE rb_fiber_scheduler_timeout_after(VALUE scheduler, VALUE timeout, VALUE exception, VALUE message) { @@ -191,6 +318,24 @@ rb_fiber_scheduler_timeout_afterv(VALUE scheduler, int argc, VALUE * argv) } #endif +/* + * Document-method: Fiber::Scheduler#process_wait + * call-seq: process_wait(pid, flags) + * + * Invoked by Process::Status.wait in order to wait for a specified process. + * See that method description for arguments description. + * + * Suggested minimal implementation: + * + * Thread.new do + * Process::Status.wait(pid, flags) + * end.value + * + * This hook is optional: if it is not present in the current scheduler, + * Process::Status.wait will behave as a blocking method. + * + * Expected to return a Process::Status instance. + */ VALUE rb_fiber_scheduler_process_wait(VALUE scheduler, rb_pid_t pid, int flags) { @@ -201,12 +346,39 @@ rb_fiber_scheduler_process_wait(VALUE scheduler, rb_pid_t pid, int flags) return rb_check_funcall(scheduler, id_process_wait, 2, arguments); } +/* + * Document-method: Fiber::Scheduler#block + * call-seq: block(blocker, timeout = nil) + * + * Invoked by methods like Thread.join, and by Mutex, to signify that current + * Fiber is blocked until further notice (e.g. #unblock) or until +timeout+ has + * elapsed. + * + * +blocker+ is what we are waiting on, informational only (for debugging and + * logging). There are no guarantee about its value. + * + * Expected to return boolean, specifying whether the blocking operation was + * successful or not. + */ VALUE rb_fiber_scheduler_block(VALUE scheduler, VALUE blocker, VALUE timeout) { return rb_funcall(scheduler, id_block, 2, blocker, timeout); } +/* + * Document-method: Fiber::Scheduler#unblock + * call-seq: unblock(blocker, fiber) + * + * Invoked to wake up Fiber previously blocked with #block (for example, Mutex#lock + * calls #block and Mutex#unlock calls #unblock). The scheduler should use + * the +fiber+ parameter to understand which fiber is unblocked. + * + * +blocker+ is what was awaited for, but it is informational only (for debugging + * and logging), and it is not guaranteed to be the same value as the +blocker+ for + * #block. + * + */ VALUE rb_fiber_scheduler_unblock(VALUE scheduler, VALUE blocker, VALUE fiber) { @@ -215,6 +387,25 @@ rb_fiber_scheduler_unblock(VALUE scheduler, VALUE blocker, VALUE fiber) return rb_funcall(scheduler, id_unblock, 2, blocker, fiber); } +/* + * Document-method: Fiber::Scheduler#io_wait + * call-seq: io_wait(io, events, timeout) + * + * Invoked by IO#wait, IO#wait_readable, IO#wait_writable to ask whether the + * specified descriptor is ready for specified events within + * the specified +timeout+. + * + * +events+ is a bit mask of <tt>IO::READABLE</tt>, <tt>IO::WRITABLE</tt>, and + * <tt>IO::PRIORITY</tt>. + * + * Suggested implementation should register which Fiber is waiting for which + * resources and immediately calling Fiber.yield to pass control to other + * fibers. Then, in the #close method, the scheduler might dispatch all the + * I/O resources to fibers waiting for it. + * + * Expected to return the subset of events that are ready immediately. + * + */ VALUE rb_fiber_scheduler_io_wait(VALUE scheduler, VALUE io, VALUE events, VALUE timeout) { @@ -233,6 +424,16 @@ rb_fiber_scheduler_io_wait_writable(VALUE scheduler, VALUE io) return rb_fiber_scheduler_io_wait(scheduler, io, RB_UINT2NUM(RUBY_IO_WRITABLE), rb_io_timeout(io)); } +/* + * Document-method: Fiber::Scheduler#io_select + * call-seq: io_select(readables, writables, exceptables, timeout) + * + * Invoked by IO.select to ask whether the specified descriptors are ready for + * specified events within the specified +timeout+. + * + * Expected to return the 3-tuple of Array of IOs that are ready. + * + */ VALUE rb_fiber_scheduler_io_select(VALUE scheduler, VALUE readables, VALUE writables, VALUE exceptables, VALUE timeout) { VALUE arguments[] = { @@ -252,6 +453,33 @@ VALUE rb_fiber_scheduler_io_selectv(VALUE scheduler, int argc, VALUE *argv) return rb_check_funcall(scheduler, id_io_select, argc, argv); } +/* + * Document-method: Fiber::Scheduler#io_read + * call-seq: io_read(io, buffer, length) -> read length or -errno + * + * Invoked by IO#read to read +length+ bytes from +io+ into a specified + * +buffer+ (see IO::Buffer). + * + * The +length+ argument is the "minimum length to be read". + * If the IO buffer size is 8KiB, but the +length+ is +1024+ (1KiB), up to + * 8KiB might be read, but at least 1KiB will be. + * Generally, the only case where less data than +length+ will be read is if + * there is an error reading the data. + * + * Specifying a +length+ of 0 is valid and means try reading at least once + * and return any available data. + * + * Suggested implementation should try to read from +io+ in a non-blocking + * manner and call #io_wait if the +io+ is not ready (which will yield control + * to other fibers). + * + * See IO::Buffer for an interface available to return data. + * + * Expected to return number of bytes read, or, in case of an error, <tt>-errno</tt> + * (negated number corresponding to system's error code). + * + * The method should be considered _experimental_. + */ VALUE rb_fiber_scheduler_io_read(VALUE scheduler, VALUE io, VALUE buffer, size_t length, size_t offset) { @@ -272,6 +500,33 @@ rb_fiber_scheduler_io_pread(VALUE scheduler, VALUE io, rb_off_t from, VALUE buff return rb_check_funcall(scheduler, id_io_pread, 5, arguments); } +/* + * Document-method: Scheduler#io_write + * call-seq: io_write(io, buffer, length) -> written length or -errno + * + * Invoked by IO#write to write +length+ bytes to +io+ from + * from a specified +buffer+ (see IO::Buffer). + * + * The +length+ argument is the "(minimum) length to be written". + * If the IO buffer size is 8KiB, but the +length+ specified is 1024 (1KiB), + * at most 8KiB will be written, but at least 1KiB will be. + * Generally, the only case where less data than +length+ will be written is if + * there is an error writing the data. + * + * Specifying a +length+ of 0 is valid and means try writing at least once, + * as much data as possible. + * + * Suggested implementation should try to write to +io+ in a non-blocking + * manner and call #io_wait if the +io+ is not ready (which will yield control + * to other fibers). + * + * See IO::Buffer for an interface available to get data from buffer efficiently. + * + * Expected to return number of bytes written, or, in case of an error, <tt>-errno</tt> + * (negated number corresponding to system's error code). + * + * The method should be considered _experimental_. + */ VALUE rb_fiber_scheduler_io_write(VALUE scheduler, VALUE io, VALUE buffer, size_t length, size_t offset) { @@ -326,6 +581,38 @@ rb_fiber_scheduler_io_close(VALUE scheduler, VALUE io) return rb_check_funcall(scheduler, id_io_close, 1, arguments); } +/* + * Document-method: Fiber::Scheduler#address_resolve + * call-seq: address_resolve(hostname) -> array_of_strings or nil + * + * Invoked by any method that performs a non-reverse DNS lookup. The most + * notable method is Addrinfo.getaddrinfo, but there are many other. + * + * The method is expected to return an array of strings corresponding to ip + * addresses the +hostname+ is resolved to, or +nil+ if it can not be resolved. + * + * Fairly exhaustive list of all possible call-sites: + * + * - Addrinfo.getaddrinfo + * - Addrinfo.tcp + * - Addrinfo.udp + * - Addrinfo.ip + * - Addrinfo.new + * - Addrinfo.marshal_load + * - SOCKSSocket.new + * - TCPServer.new + * - TCPSocket.new + * - IPSocket.getaddress + * - TCPSocket.gethostbyname + * - UDPSocket#connect + * - UDPSocket#bind + * - UDPSocket#send + * - Socket.getaddrinfo + * - Socket.gethostbyname + * - Socket.pack_sockaddr_in + * - Socket.sockaddr_in + * - Socket.unpack_sockaddr_in + */ VALUE rb_fiber_scheduler_address_resolve(VALUE scheduler, VALUE hostname) { @@ -335,3 +622,24 @@ rb_fiber_scheduler_address_resolve(VALUE scheduler, VALUE hostname) return rb_check_funcall(scheduler, id_address_resolve, 1, arguments); } + +/* + * Document-method: Fiber::Scheduler#fiber + * call-seq: fiber(&block) + * + * Implementation of the Fiber.schedule. The method is <em>expected</em> to immediately + * run the given block of code in a separate non-blocking fiber, and to return that Fiber. + * + * Minimal suggested implementation is: + * + * def fiber(&block) + * fiber = Fiber.new(blocking: false, &block) + * fiber.resume + * fiber + * end + */ +VALUE +rb_fiber_scheduler_fiber(VALUE scheduler, int argc, VALUE *argv, int kw_splat) +{ + return rb_funcall_passing_block_kw(scheduler, id_fiber_schedule, argc, argv, kw_splat); +} |