Class: Thread

Inherits:
Object show all
Defined in:
vm.c,
vm.c

Overview

Threads are the Ruby implementation for a concurrent programming model.

Programs that require multiple threads of execution are a perfect candidate for Ruby's Thread class.

For example, we can create a new thread separate from the main thread's execution using ::new.

thr = Thread.new { puts "What's the big deal" }

Then we are able to pause the execution of the main thread and allow our new thread to finish, using #join:

thr.join #=> "What's the big deal"

If we don't call thr.join before the main thread terminates, then all other threads including thr will be killed.

Alternatively, you can use an array for handling multiple threads at once, like in the following example:

threads = []
threads << Thread.new { puts "What's the big deal" }
threads << Thread.new { 3.times { puts "Threads are fun!" } }

After creating a few threads we wait for them all to finish consecutively.

   threads.each { |thr| thr.join }

To retrieve the last value of a thread, use #value

    thr = Thread.new { sleep 1; "Useful value" }
    thr.value #=> "Useful value"

Thread initialization

In order to create new threads, Ruby provides ::new, ::start, and ::fork. A block must be provided with each of these methods, otherwise a ThreadError will be raised.

When subclassing the Thread class, the initialize method of your subclass will be ignored by ::start and ::fork. Otherwise, be sure to call super in your initialize method.

=== Thread termination

For terminating threads, Ruby provides a variety of ways to do this.

The class method ::kill, is meant to exit a given thread:

thr = Thread.new { sleep }
Thread.kill(thr) # sends exit() to thr

Alternatively, you can use the instance method #exit, or any of its aliases #kill or #terminate.

thr.exit

=== Thread status

Ruby provides a few instance methods for querying the state of a given thread. To get a string with the current thread's state use #status

thr = Thread.new { sleep }
thr.status # => "sleep"
thr.exit
thr.status # => false

You can also use #alive? to tell if the thread is running or sleeping, and #stop? if the thread is dead or sleeping.

=== Thread variables and scope

Since threads are created with blocks, the same rules apply to other Ruby blocks for variable scope. Any local variables created within this block are accessible to only this thread.

==== Fiber-local vs. Thread-local

Each fiber has its own bucket for Thread#[] storage. When you set a new fiber-local it is only accessible within this Fiber. To illustrate:

Thread.new {
  Thread.current[:foo] = "bar"
  Fiber.new {
    p Thread.current[:foo] # => nil
  }.resume
}.join

This example uses #[] for getting and #[]= for setting fiber-locals, you can also use #keys to list the fiber-locals for a given thread and #key? to check if a fiber-local exists.

When it comes to thread-locals, they are accessible within the entire scope of the thread. Given the following example:

Thread.new{
  Thread.current.thread_variable_set(:foo, 1)
  p Thread.current.thread_variable_get(:foo) # => 1
  Fiber.new{

Thread.current.thread_variable_set(:foo, 2) p Thread.current.thread_variable_get(:foo) # => 2

     }.resume
     p Thread.current.thread_variable_get(:foo)   # => 2
   }.join

You can see that the thread-local +:foo+ carried over into the fiber
and was changed to +2+ by the end of the thread.

This example makes use of #thread_variable_set to create new
thread-locals, and #thread_variable_get to reference them.

There is also #thread_variables to list all thread-locals, and
#thread_variable? to check if a given thread-local exists.

=== Exception handling

When an unhandled exception is raised inside a thread, it will
terminate. By default, this exception will not propagate to other
threads. The exception is stored and when another thread calls #value
or #join, the exception will be re-raised in that thread.

    t = Thread.new{ raise 'something went wrong' }
    t.value #=> RuntimeError: something went wrong

An exception can be raised from outside the thread using the
Thread#raise instance method, which takes the same parameters as
Kernel#raise.

Setting Thread.abort_on_exception = true, Thread#abort_on_exception =
true, or $DEBUG = true will cause a subsequent unhandled exception
raised in a thread to be automatically re-raised in the main thread.

With the addition of the class method ::handle_interrupt, you can now handle exceptions asynchronously with threads.

=== Scheduling

Ruby provides a few ways to support scheduling threads in your program.

The first way is by using the class method ::stop, to put the current running thread to sleep and schedule the execution of another thread.

Once a thread is asleep, you can use the instance method #wakeup to mark your thread as eligible for scheduling.

You can also try ::pass, which attempts to pass execution to another thread but is dependent on the OS whether a running thread will switch or not. The same goes for #priority, which lets you hint to the thread scheduler which threads you want to take precedence when passing execution. This method is also dependent on the OS and may be ignored on some platforms.

Direct Known Subclasses

Process::Waiter

Defined Under Namespace

Classes: Backtrace

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(args) ⇒ Object

:nodoc:


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# File 'thread.c', line 952

static VALUE
thread_initialize(VALUE thread, VALUE args)
{
    rb_thread_t *th = rb_thread_ptr(thread);

    if (!rb_block_given_p()) {
        rb_raise(rb_eThreadError, "must be called with a block");
    }
    else if (th->invoke_type != thread_invoke_type_none) {
        VALUE loc = threadptr_invoke_proc_location(th);
        if (!NIL_P(loc)) {
            rb_raise(rb_eThreadError,
                     "already initialized thread - %"PRIsVALUE":%"PRIsVALUE,
                     RARRAY_AREF(loc, 0), RARRAY_AREF(loc, 1));
        }
        else {
            rb_raise(rb_eThreadError, "already initialized thread");
        }
    }
    else {
        return thread_create_core(thread, args, NULL);
    }
}

Class Method Details

.abort_on_exceptionBoolean

Returns the status of the global “abort on exception'' condition.

The default is false.

When set to true, if any thread is aborted by an exception, the raised exception will be re-raised in the main thread.

Can also be specified by the global $DEBUG flag or command line option -d.

See also ::abort_on_exception=.

There is also an instance level method to set this for a specific thread, see #abort_on_exception.

Returns:

  • (Boolean)

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# File 'thread.c', line 2757

static VALUE
rb_thread_s_abort_exc(VALUE _)
{
    return GET_THREAD()->vm->thread_abort_on_exception ? Qtrue : Qfalse;
}

.abort_on_exception=(boolean) ⇒ Boolean

When set to true, if any thread is aborted by an exception, the raised exception will be re-raised in the main thread. Returns the new state.

Thread.abort_on_exception = true
t1 = Thread.new do
  puts  "In new thread"
  raise "Exception from thread"
end
sleep(1)
puts "not reached"

This will produce:

In new thread
prog.rb:4: Exception from thread (RuntimeError)
	from prog.rb:2:in `initialize'
	from prog.rb:2:in `new'
	from prog.rb:2

See also ::abort_on_exception.

There is also an instance level method to set this for a specific thread, see #abort_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2794

static VALUE
rb_thread_s_abort_exc_set(VALUE self, VALUE val)
{
    GET_THREAD()->vm->thread_abort_on_exception = RTEST(val);
    return val;
}

.currentObject

Returns the currently executing thread.

Thread.current   #=> #<Thread:0x401bdf4c run>

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# File 'thread.c', line 2711

static VALUE
thread_s_current(VALUE klass)
{
    return rb_thread_current();
}

.DEBUGNumeric

Returns the thread debug level. Available only if compiled with THREAD_DEBUG=-1.

Returns:


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# File 'thread.c', line 317

static VALUE
rb_thread_s_debug(void)
{
    return INT2NUM(rb_thread_debug_enabled);
}

.DEBUG=(num) ⇒ Object

Sets the thread debug level. Available only if compiled with THREAD_DEBUG=-1.


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# File 'thread.c', line 331

static VALUE
rb_thread_s_debug_set(VALUE self, VALUE val)
{
    rb_thread_debug_enabled = RTEST(val) ? NUM2INT(val) : 0;
    return val;
}

.exitObject

Terminates the currently running thread and schedules another thread to be run.

If this thread is already marked to be killed, ::exit returns the Thread.

If this is the main thread, or the last thread, exit the process.


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# File 'thread.c', line 2536

static VALUE
rb_thread_exit(VALUE _)
{
    rb_thread_t *th = GET_THREAD();
    return rb_thread_kill(th->self);
}

.start([args]) {|args| ... } ⇒ Object .fork([args]) {|args| ... } ⇒ Object

Basically the same as ::new. However, if class Thread is subclassed, then calling start in that subclass will not invoke the subclass's initialize method.

Overloads:

  • .start([args]) {|args| ... } ⇒ Object

    Yields:

    • (args)
  • .fork([args]) {|args| ... } ⇒ Object

    Yields:

    • (args)

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# File 'thread.c', line 934

static VALUE
thread_start(VALUE klass, VALUE args)
{
    return thread_create_core(rb_thread_alloc(klass), args, 0);
}

.handle_interrupt(hash) { ... } ⇒ Object

Changes asynchronous interrupt timing.

interrupt means asynchronous event and corresponding procedure by Thread#raise, Thread#kill, signal trap (not supported yet) and main thread termination (if main thread terminates, then all other thread will be killed).

The given hash has pairs like ExceptionClass => :TimingSymbol. Where the ExceptionClass is the interrupt handled by the given block. The TimingSymbol can be one of the following symbols:

:immediate

Invoke interrupts immediately.

:on_blocking

Invoke interrupts while BlockingOperation.

:never

Never invoke all interrupts.

BlockingOperation means that the operation will block the calling thread, such as read and write. On CRuby implementation, BlockingOperation is any operation executed without GVL.

Masked asynchronous interrupts are delayed until they are enabled. This method is similar to sigprocmask(3).

NOTE

Asynchronous interrupts are difficult to use.

If you need to communicate between threads, please consider to use another way such as Queue.

Or use them with deep understanding about this method.

Usage

In this example, we can guard from Thread#raise exceptions.

Using the :never TimingSymbol the RuntimeError exception will always be ignored in the first block of the main thread. In the second ::handle_interrupt block we can purposefully handle RuntimeError exceptions.

th = Thread.new do
  Thread.handle_interrupt(RuntimeError => :never) {
    begin
      # You can write resource allocation code safely.
      Thread.handle_interrupt(RuntimeError => :immediate) {
   # ...
      }
    ensure
      # You can write resource deallocation code safely.
    end
  }
end
Thread.pass# ...

th.raise "stop"

While we are ignoring the RuntimeError exception, it's safe to write our resource allocation code. Then, the ensure block is where we can safely deallocate your resources.

Guarding from Timeout::Error

In the next example, we will guard from the Timeout::Error exception. This will help prevent from leaking resources when Timeout::Error exceptions occur during normal ensure clause. For this example we use the help of the standard library Timeout, from lib/timeout.rb

require 'timeout'
Thread.handle_interrupt(Timeout::Error => :never) {
  timeout(10){
    # Timeout::Error doesn't occur here
    Thread.handle_interrupt(Timeout::Error => :on_blocking) {
      # possible to be killed by Timeout::Error
      # while blocking operation
    }    # Timeout::Error doesn't occur here

  }
}

In the first part of the timeout block, we can rely on Timeout::Error being ignored. Then in the Timeout::Error => :on_blocking block, any operation that will block the calling thread is susceptible to a Timeout::Error exception being raised.

Stack control settings

It's possible to stack multiple levels of ::handle_interrupt blocks in order to control more than one ExceptionClass and TimingSymbol at a time.

Thread.handle_interrupt(FooError => :never) {
  Thread.handle_interrupt(BarError => :never) {
     # FooError and BarError are prohibited.
  }
}

Inheritance with ExceptionClass

All exceptions inherited from the ExceptionClass parameter will be considered.

Thread.handle_interrupt(Exception => :never) {
  # all exceptions inherited from Exception are prohibited.
}

Yields:


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# File 'thread.c', line 2040

static VALUE
rb_thread_s_handle_interrupt(VALUE self, VALUE mask_arg)
{
    VALUE mask;
    rb_execution_context_t * volatile ec = GET_EC();
    rb_thread_t * volatile th = rb_ec_thread_ptr(ec);
    volatile VALUE r = Qnil;
    enum ruby_tag_type state;

    if (!rb_block_given_p()) {
	rb_raise(rb_eArgError, "block is needed.");
    }

    mask = 0;
    mask_arg = rb_to_hash_type(mask_arg);
    rb_hash_foreach(mask_arg, handle_interrupt_arg_check_i, (VALUE)&mask);
    if (!mask) {
	return rb_yield(Qnil);
    }
    OBJ_FREEZE_RAW(mask);
    rb_ary_push(th->pending_interrupt_mask_stack, mask);
    if (!rb_threadptr_pending_interrupt_empty_p(th)) {
	th->pending_interrupt_queue_checked = 0;
	RUBY_VM_SET_INTERRUPT(th->ec);
    }

    EC_PUSH_TAG(th->ec);
    if ((state = EC_EXEC_TAG()) == TAG_NONE) {
	r = rb_yield(Qnil);
    }
    EC_POP_TAG();

    rb_ary_pop(th->pending_interrupt_mask_stack);
    if (!rb_threadptr_pending_interrupt_empty_p(th)) {
	th->pending_interrupt_queue_checked = 0;
	RUBY_VM_SET_INTERRUPT(th->ec);
    }

    RUBY_VM_CHECK_INTS(th->ec);

    if (state) {
	EC_JUMP_TAG(th->ec, state);
    }

    return r;
}

.kill(thread) ⇒ Object

Causes the given thread to exit, see also Thread::exit.

count = 0
a = Thread.new { loop { count += 1 } }
sleep(0.1)       #=> 0
Thread.kill(a)   #=> #<Thread:0x401b3d30 dead>
count            #=> 93947
a.alive?         #=> false

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# File 'thread.c', line 2517

static VALUE
rb_thread_s_kill(VALUE obj, VALUE th)
{
    return rb_thread_kill(th);
}

.listArray

Returns an array of Thread objects for all threads that are either runnable or stopped.

Thread.new { sleep(200) }
Thread.new { 1000000.times {|i| i*i } }
Thread.new { Thread.stop }
Thread.list.each {|t| p t}

This will produce:

#<Thread:0x401b3e84 sleep>
#<Thread:0x401b3f38 run>
#<Thread:0x401b3fb0 sleep>
#<Thread:0x401bdf4c run>

Returns:


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# File 'thread.c', line 2690

static VALUE
thread_list(VALUE _)
{
    return rb_thread_list();
}

.mainObject

Returns the main thread.


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# File 'thread.c', line 2730

static VALUE
rb_thread_s_main(VALUE klass)
{
    return rb_thread_main();
}

.new(*args) ⇒ Object

Thread.new(*args, &proc) -> thread

Thread.new(*args) { |args| ... }	-> thread

Creates a new thread executing the given block.

Any +args+ given to ::new will be passed to the block:

arr = [] a, b, c = 1, 2, 3 Thread.new(a,b,c) { |d,e,f| arr << d << e << f }.join arr #=> [1, 2, 3]

A ThreadError exception is raised if ::new is called without a block.

If you're going to subclass Thread, be sure to call super in your
+initialize+ method, otherwise a ThreadError will be raised.

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# File 'thread.c', line 906

static VALUE
thread_s_new(int argc, VALUE *argv, VALUE klass)
{
    rb_thread_t *th;
    VALUE thread = rb_thread_alloc(klass);

    if (GET_VM()->main_thread->status == THREAD_KILLED)
	rb_raise(rb_eThreadError, "can't alloc thread");

    rb_obj_call_init_kw(thread, argc, argv, RB_PASS_CALLED_KEYWORDS);
    th = rb_thread_ptr(thread);
    if (!threadptr_initialized(th)) {
	rb_raise(rb_eThreadError, "uninitialized thread - check `%"PRIsVALUE"#initialize'",
		 klass);
    }
    return thread;
}

.passnil

Give the thread scheduler a hint to pass execution to another thread. A running thread may or may not switch, it depends on OS and processor.

Returns:

  • (nil)

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# File 'thread.c', line 1746

static VALUE
thread_s_pass(VALUE klass)
{
    rb_thread_schedule();
    return Qnil;
}

.pending_interrupt?(error = nil) ⇒ Boolean

Returns whether or not the asynchronous queue is empty.

Since Thread::handle_interrupt can be used to defer asynchronous events, this method can be used to determine if there are any deferred events.

If you find this method returns true, then you may finish :never blocks.

For example, the following method processes deferred asynchronous events immediately.

def Thread.kick_interrupt_immediately
  Thread.handle_interrupt(Object => :immediate) {
    Thread.pass
  }
end

If error is given, then check only for error type deferred events.

Usage

th = Thread.new{
  Thread.handle_interrupt(RuntimeError => :on_blocking){
    while true
      ...
      # reach safe point to invoke interrupt
      if Thread.pending_interrupt?
        Thread.handle_interrupt(Object => :immediate){}
      end
      ...
    end
  }
}
...
th.raise # stop thread

This example can also be written as the following, which you should use to avoid asynchronous interrupts.

flag = true
th = Thread.new{
  Thread.handle_interrupt(RuntimeError => :on_blocking){
    while true
      ...
      # reach safe point to invoke interrupt
      break if flag == false
      ...
    end
  }
}
...
flag = false # stop thread

Returns:

  • (Boolean)

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# File 'thread.c', line 2182

static VALUE
rb_thread_s_pending_interrupt_p(int argc, VALUE *argv, VALUE self)
{
    return rb_thread_pending_interrupt_p(argc, argv, GET_THREAD()->self);
}

.report_on_exceptionBoolean

Returns the status of the global “report on exception'' condition.

The default is true since Ruby 2.5.

All threads created when this flag is true will report a message on $stderr if an exception kills the thread.

Thread.new { 1.times { raise } }

will produce this output on $stderr:

#<Thread:...> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
        2: from -e:1:in `block in <main>'
        1: from -e:1:in `times'

This is done to catch errors in threads early. In some cases, you might not want this output. There are multiple ways to avoid the extra output:

  • If the exception is not intended, the best is to fix the cause of the exception so it does not happen anymore.

  • If the exception is intended, it might be better to rescue it closer to where it is raised rather then let it kill the Thread.

  • If it is guaranteed the Thread will be joined with Thread#join or Thread#value, then it is safe to disable this report with Thread.current.report_on_exception = false when starting the Thread. However, this might handle the exception much later, or not at all if the Thread is never joined due to the parent thread being blocked, etc.

See also ::report_on_exception=.

There is also an instance level method to set this for a specific thread, see #report_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2887

static VALUE
rb_thread_s_report_exc(VALUE _)
{
    return GET_THREAD()->vm->thread_report_on_exception ? Qtrue : Qfalse;
}

.report_on_exception=(boolean) ⇒ Boolean

Returns the new state. When set to true, all threads created afterwards will inherit the condition and report a message on $stderr if an exception kills a thread:

Thread.report_on_exception = true
t1 = Thread.new do
  puts  "In new thread"
  raise "Exception from thread"
end
sleep(1)
puts "In the main thread"

This will produce:

In new thread
#<Thread:...prog.rb:2> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
prog.rb:4:in `block in <main>': Exception from thread (RuntimeError)
In the main thread

See also ::report_on_exception.

There is also an instance level method to set this for a specific thread, see #report_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2924

static VALUE
rb_thread_s_report_exc_set(VALUE self, VALUE val)
{
    GET_THREAD()->vm->thread_report_on_exception = RTEST(val);
    return val;
}

.start([args]) {|args| ... } ⇒ Object .fork([args]) {|args| ... } ⇒ Object

Basically the same as ::new. However, if class Thread is subclassed, then calling start in that subclass will not invoke the subclass's initialize method.

Overloads:

  • .start([args]) {|args| ... } ⇒ Object

    Yields:

    • (args)
  • .fork([args]) {|args| ... } ⇒ Object

    Yields:

    • (args)

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# File 'thread.c', line 934

static VALUE
thread_start(VALUE klass, VALUE args)
{
    return thread_create_core(rb_thread_alloc(klass), args, 0);
}

.stopnil

Stops execution of the current thread, putting it into a “sleep'' state, and schedules execution of another thread.

a = Thread.new { print "a"; Thread.stop; print "c" }
sleep 0.1 while a.status!='sleep'
print "b"
a.run
a.join#=> "abc"

Returns:

  • (nil)

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# File 'thread.c', line 2642

static VALUE
thread_stop(VALUE _)
{
    return rb_thread_stop();
}

Instance Method Details

#[](sym) ⇒ Object?

Attribute Reference—Returns the value of a fiber-local variable (current thread's root fiber if not explicitly inside a Fiber), using either a symbol or a string name. If the specified variable does not exist, returns nil.

[
  Thread.new { Thread.current["name"] = "A" },
  Thread.new { Thread.current[:name]  = "B" },
  Thread.new { Thread.current["name"] = "C" }
].each do |th|
  th.join
  puts "#{th.inspect}: #{th[:name]}"
end

This will produce:

#<Thread:0x00000002a54220 dead>: A
#<Thread:0x00000002a541a8 dead>: B
#<Thread:0x00000002a54130 dead>: C

Thread#[] and Thread#[]= are not thread-local but fiber-local. This confusion did not exist in Ruby 1.8 because fibers are only available since Ruby 1.9. Ruby 1.9 chooses that the methods behaves fiber-local to save following idiom for dynamic scope.

def meth(newvalue)
  begin
    oldvalue = Thread.current[:name]
    Thread.current[:name] = newvalue
    yield
  ensure
    Thread.current[:name] = oldvalue
  end
end

The idiom may not work as dynamic scope if the methods are thread-local and a given block switches fiber.

f = Fiber.new {
  meth(1) {
    Fiber.yield
  }
}
meth(2) {
  f.resume
}
f.resume
p Thread.current[:name]#=> nil if fiber-local
#=> 2 if thread-local (The value 2 is leaked to outside of meth method.)

For thread-local variables, please see #thread_variable_get and #thread_variable_set.

Returns:


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# File 'thread.c', line 3302

static VALUE
rb_thread_aref(VALUE thread, VALUE key)
{
    ID id = rb_check_id(&key);
    if (!id) return Qnil;
    return rb_thread_local_aref(thread, id);
}

#[]=(sym) ⇒ Object

Attribute Assignment—Sets or creates the value of a fiber-local variable, using either a symbol or a string.

See also Thread#[].

For thread-local variables, please see #thread_variable_set and #thread_variable_get.

Returns:


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# File 'thread.c', line 3407

static VALUE
rb_thread_aset(VALUE self, VALUE id, VALUE val)
{
    return rb_thread_local_aset(self, rb_to_id(id), val);
}

#abort_on_exceptionBoolean

Returns the status of the thread-local “abort on exception'' condition for this thr.

The default is false.

See also #abort_on_exception=.

There is also a class level method to set this for all threads, see ::abort_on_exception.

Returns:

  • (Boolean)

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# File 'thread.c', line 2817

static VALUE
rb_thread_abort_exc(VALUE thread)
{
    return rb_thread_ptr(thread)->abort_on_exception ? Qtrue : Qfalse;
}

#abort_on_exception=(boolean) ⇒ Boolean

When set to true, if this thr is aborted by an exception, the raised exception will be re-raised in the main thread.

See also #abort_on_exception.

There is also a class level method to set this for all threads, see ::abort_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2837

static VALUE
rb_thread_abort_exc_set(VALUE thread, VALUE val)
{
    rb_thread_ptr(thread)->abort_on_exception = RTEST(val);
    return val;
}

#add_trace_func(proc) ⇒ Proc

Adds proc as a handler for tracing.

See Thread#set_trace_func and Kernel#set_trace_func.

Returns:


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# File 'vm_trace.c', line 553

static VALUE
thread_add_trace_func_m(VALUE obj, VALUE trace)
{
    thread_add_trace_func(GET_EC(), rb_thread_ptr(obj), trace);
    return trace;
}

#alive?Boolean

Returns true if thr is running or sleeping.

thr = Thread.new { }
thr.join                #=> #<Thread:0x401b3fb0 dead>
Thread.current.alive?   #=> true
thr.alive?              #=> false

See also #stop? and #status.

Returns:

  • (Boolean)

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# File 'thread.c', line 3082

static VALUE
rb_thread_alive_p(VALUE thread)
{
    if (rb_threadptr_dead(rb_thread_ptr(thread))) {
	return Qfalse;
    }
    else {
	return Qtrue;
    }
}

#backtraceArray

Returns the current backtrace of the target thread.

Returns:


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# File 'thread.c', line 5144

static VALUE
rb_thread_backtrace_m(int argc, VALUE *argv, VALUE thval)
{
    return rb_vm_thread_backtrace(argc, argv, thval);
}

#backtrace_locations(*args) ⇒ Object

Returns the execution stack for the target thread—an array containing backtrace location objects.

See Thread::Backtrace::Location for more information.

This method behaves similarly to Kernel#caller_locations except it applies to a specific thread.


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# File 'thread.c', line 5161

static VALUE
rb_thread_backtrace_locations_m(int argc, VALUE *argv, VALUE thval)
{
    return rb_vm_thread_backtrace_locations(argc, argv, thval);
}

#exitObject #killObject #terminateObject

Terminates thr and schedules another thread to be run, returning the terminated Thread. If this is the main thread, or the last thread, exits the process.


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# File 'thread.c', line 2466

VALUE
rb_thread_kill(VALUE thread)
{
    rb_thread_t *th = rb_thread_ptr(thread);

    if (th->to_kill || th->status == THREAD_KILLED) {
	return thread;
    }
    if (th == th->vm->main_thread) {
	rb_exit(EXIT_SUCCESS);
    }

    thread_debug("rb_thread_kill: %p (%"PRI_THREAD_ID")\n", (void *)th, thread_id_str(th));

    if (th == GET_THREAD()) {
	/* kill myself immediately */
	rb_threadptr_to_kill(th);
    }
    else {
	threadptr_check_pending_interrupt_queue(th);
	rb_threadptr_pending_interrupt_enque(th, eKillSignal);
	rb_threadptr_interrupt(th);
    }
    return thread;
}

#fetch(sym) ⇒ Object #fetch(sym) { ... } ⇒ Object #fetch(sym, default) ⇒ Object

Returns a fiber-local for the given key. If the key can't be found, there are several options: With no other arguments, it will raise a KeyError exception; if default is given, then that will be returned; if the optional code block is specified, then that will be run and its result returned. See Thread#[] and Hash#fetch.

Overloads:


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# File 'thread.c', line 3323

static VALUE
rb_thread_fetch(int argc, VALUE *argv, VALUE self)
{
    VALUE key, val;
    ID id;
    rb_thread_t *target_th = rb_thread_ptr(self);
    int block_given;

    rb_check_arity(argc, 1, 2);
    key = argv[0];

    block_given = rb_block_given_p();
    if (block_given && argc == 2) {
	rb_warn("block supersedes default value argument");
    }

    id = rb_check_id(&key);

    if (id == recursive_key) {
	return target_th->ec->local_storage_recursive_hash;
    }
    else if (id && target_th->ec->local_storage &&
	     st_lookup(target_th->ec->local_storage, id, &val)) {
	return val;
    }
    else if (block_given) {
	return rb_yield(key);
    }
    else if (argc == 1) {
	rb_key_err_raise(rb_sprintf("key not found: %+"PRIsVALUE, key), self, key);
    }
    else {
	return argv[1];
    }
}

#groupnil

Returns the ThreadGroup which contains the given thread, or returns nil if thr is not a member of any group.

Thread.main.group   #=> #<ThreadGroup:0x4029d914>

Returns:

  • (nil)

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# File 'thread.c', line 2986

VALUE
rb_thread_group(VALUE thread)
{
    VALUE group = rb_thread_ptr(thread)->thgroup;
    return group == 0 ? Qnil : group;
}

#joinObject #join(limit) ⇒ Object

The calling thread will suspend execution and run this thr.

Does not return until thr exits or until the given limit seconds have passed.

If the time limit expires, nil will be returned, otherwise thr is returned.

Any threads not joined will be killed when the main program exits.

If thr had previously raised an exception and the ::abort_on_exception or $DEBUG flags are not set, (so the exception has not yet been processed), it will be processed at this time.

a = Thread.new { print "a"; sleep(10); print "b"; print "c" }
x = Thread.new { print "x"; Thread.pass; print "y"; print "z" }
x.join # Let thread x finish, thread a will be killed on exit.
#=> "axyz"

The following example illustrates the limit parameter.

y = Thread.new { 4.times { sleep 0.1; puts 'tick... ' }}
puts "Waiting" until y.join(0.15)

This will produce:

tick...
Waiting
tick...
Waiting
tick...
tick...

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# File 'thread.c', line 1146

static VALUE
thread_join_m(int argc, VALUE *argv, VALUE self)
{
    VALUE limit;
    rb_hrtime_t rel, *to = 0;

    /*
     * This supports INFINITY and negative values, so we can't use
     * rb_time_interval right now...
     */
    if (!rb_check_arity(argc, 0, 1) || NIL_P(argv[0])) {
        /* unlimited */
    }
    else if (FIXNUM_P(limit = argv[0])) {
        rel = rb_sec2hrtime(NUM2TIMET(limit));
        to = &rel;
    }
    else {
        to = double2hrtime(&rel, rb_num2dbl(limit));
    }

    return thread_join(rb_thread_ptr(self), to);
}

#key?(sym) ⇒ Boolean

Returns true if the given string (or symbol) exists as a fiber-local variable.

me = Thread.current
me[:oliver] = "a"
me.key?(:oliver)    #=> true
me.key?(:stanley)   #=> false

Returns:

  • (Boolean)

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# File 'thread.c', line 3488

static VALUE
rb_thread_key_p(VALUE self, VALUE key)
{
    ID id = rb_check_id(&key);
    st_table *local_storage = rb_thread_ptr(self)->ec->local_storage;

    if (!id || local_storage == NULL) {
	return Qfalse;
    }
    else if (st_is_member(local_storage, id)) {
	return Qtrue;
    }
    else {
	return Qfalse;
    }
}

#keysArray

Returns an array of the names of the fiber-local variables (as Symbols).

thr = Thread.new do
  Thread.current[:cat] = 'meow'
  Thread.current["dog"] = 'woof'
end
thr.join   #=> #<Thread:0x401b3f10 dead>
thr.keys   #=> [:dog, :cat]

Returns:


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# File 'thread.c', line 3532

static VALUE
rb_thread_keys(VALUE self)
{
    st_table *local_storage = rb_thread_ptr(self)->ec->local_storage;
    VALUE ary = rb_ary_new();

    if (local_storage) {
	st_foreach(local_storage, thread_keys_i, ary);
    }
    return ary;
}

#exitObject #killObject #terminateObject

Terminates thr and schedules another thread to be run, returning the terminated Thread. If this is the main thread, or the last thread, exits the process.


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# File 'thread.c', line 2466

VALUE
rb_thread_kill(VALUE thread)
{
    rb_thread_t *th = rb_thread_ptr(thread);

    if (th->to_kill || th->status == THREAD_KILLED) {
	return thread;
    }
    if (th == th->vm->main_thread) {
	rb_exit(EXIT_SUCCESS);
    }

    thread_debug("rb_thread_kill: %p (%"PRI_THREAD_ID")\n", (void *)th, thread_id_str(th));

    if (th == GET_THREAD()) {
	/* kill myself immediately */
	rb_threadptr_to_kill(th);
    }
    else {
	threadptr_check_pending_interrupt_queue(th);
	rb_threadptr_pending_interrupt_enque(th, eKillSignal);
	rb_threadptr_interrupt(th);
    }
    return thread;
}

#nameString

show the name of the thread.

Returns:


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# File 'thread.c', line 3148

static VALUE
rb_thread_getname(VALUE thread)
{
    return rb_thread_ptr(thread)->name;
}

#name=(name) ⇒ String

set given name to the ruby thread. On some platform, it may set the name to pthread and/or kernel.

Returns:


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# File 'thread.c', line 3162

static VALUE
rb_thread_setname(VALUE thread, VALUE name)
{
    rb_thread_t *target_th = rb_thread_ptr(thread);

    if (!NIL_P(name)) {
	rb_encoding *enc;
	StringValueCStr(name);
	enc = rb_enc_get(name);
	if (!rb_enc_asciicompat(enc)) {
	    rb_raise(rb_eArgError, "ASCII incompatible encoding (%s)",
		     rb_enc_name(enc));
	}
	name = rb_str_new_frozen(name);
    }
    target_th->name = name;
    if (threadptr_initialized(target_th)) {
	native_set_another_thread_name(target_th->thread_id, name);
    }
    return name;
}

#pending_interrupt?(error = nil) ⇒ Boolean

Returns whether or not the asynchronous queue is empty for the target thread.

If error is given, then check only for error type deferred events.

See ::pending_interrupt? for more information.

Returns:

  • (Boolean)

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# File 'thread.c', line 2097

static VALUE
rb_thread_pending_interrupt_p(int argc, VALUE *argv, VALUE target_thread)
{
    rb_thread_t *target_th = rb_thread_ptr(target_thread);

    if (!target_th->pending_interrupt_queue) {
	return Qfalse;
    }
    if (rb_threadptr_pending_interrupt_empty_p(target_th)) {
	return Qfalse;
    }
    if (rb_check_arity(argc, 0, 1)) {
        VALUE err = argv[0];
        if (!rb_obj_is_kind_of(err, rb_cModule)) {
            rb_raise(rb_eTypeError, "class or module required for rescue clause");
        }
        if (rb_threadptr_pending_interrupt_include_p(target_th, err)) {
            return Qtrue;
        }
        else {
            return Qfalse;
        }
    }
    else {
	return Qtrue;
    }
}

#priorityInteger

Returns the priority of thr. Default is inherited from the current thread which creating the new thread, or zero for the initial main thread; higher-priority thread will run more frequently than lower-priority threads (but lower-priority threads can also run).

This is just hint for Ruby thread scheduler. It may be ignored on some platform.

Thread.current.priority   #=> 0

Returns:


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# File 'thread.c', line 3638

static VALUE
rb_thread_priority(VALUE thread)
{
    return INT2NUM(rb_thread_ptr(thread)->priority);
}

#priority=(integer) ⇒ Object

Sets the priority of thr to integer. Higher-priority threads will run more frequently than lower-priority threads (but lower-priority threads can also run).

This is just hint for Ruby thread scheduler. It may be ignored on some platform.

count1 = count2 = 0
a = Thread.new do
      loop { count1 += 1 }
    end
a.priority = -1

b = Thread.new do
      loop { count2 += 1 }
    end
b.priority = -2
sleep 1   #=> 1
count1    #=> 622504
count2    #=> 5832

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# File 'thread.c', line 3671

static VALUE
rb_thread_priority_set(VALUE thread, VALUE prio)
{
    rb_thread_t *target_th = rb_thread_ptr(thread);
    int priority;

#if USE_NATIVE_THREAD_PRIORITY
    target_th->priority = NUM2INT(prio);
    native_thread_apply_priority(th);
#else
    priority = NUM2INT(prio);
    if (priority > RUBY_THREAD_PRIORITY_MAX) {
	priority = RUBY_THREAD_PRIORITY_MAX;
    }
    else if (priority < RUBY_THREAD_PRIORITY_MIN) {
	priority = RUBY_THREAD_PRIORITY_MIN;
    }
    target_th->priority = (int8_t)priority;
#endif
    return INT2NUM(target_th->priority);
}

#raiseObject #raise(string) ⇒ Object #raise(exception[, string [, array]]) ⇒ Object

Raises an exception from the given thread. The caller does not have to be thr. See Kernel#raise for more information.

Thread.abort_on_exception = true
a = Thread.new { sleep(200) }
a.raise("Gotcha")

This will produce:

prog.rb:3: Gotcha (RuntimeError)
	from prog.rb:2:in `initialize'
	from prog.rb:2:in `new'
	from prog.rb:2

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# File 'thread.c', line 2438

static VALUE
thread_raise_m(int argc, VALUE *argv, VALUE self)
{
    rb_thread_t *target_th = rb_thread_ptr(self);
    const rb_thread_t *current_th = GET_THREAD();

    threadptr_check_pending_interrupt_queue(target_th);
    rb_threadptr_raise(target_th, argc, argv);

    /* To perform Thread.current.raise as Kernel.raise */
    if (current_th == target_th) {
	RUBY_VM_CHECK_INTS(target_th->ec);
    }
    return Qnil;
}

#report_on_exceptionBoolean

Returns the status of the thread-local “report on exception'' condition for this thr.

The default value when creating a Thread is the value of the global flag Thread.report_on_exception.

See also #report_on_exception=.

There is also a class level method to set this for all new threads, see ::report_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2948

static VALUE
rb_thread_report_exc(VALUE thread)
{
    return rb_thread_ptr(thread)->report_on_exception ? Qtrue : Qfalse;
}

#report_on_exception=(boolean) ⇒ Boolean

When set to true, a message is printed on $stderr if an exception kills this thr. See ::report_on_exception for details.

See also #report_on_exception.

There is also a class level method to set this for all new threads, see ::report_on_exception=.

Returns:

  • (Boolean)

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# File 'thread.c', line 2968

static VALUE
rb_thread_report_exc_set(VALUE thread, VALUE val)
{
    rb_thread_ptr(thread)->report_on_exception = RTEST(val);
    return val;
}

#runObject

Wakes up thr, making it eligible for scheduling.

a = Thread.new { puts "a"; Thread.stop; puts "c" }
sleep 0.1 while a.status!='sleep'
puts "Got here"
a.run
a.join

This will produce:

a
Got here
c

See also the instance method #wakeup.


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# File 'thread.c', line 2607

VALUE
rb_thread_run(VALUE thread)
{
    rb_thread_wakeup(thread);
    rb_thread_schedule();
    return thread;
}

#safe_levelInteger

Returns the safe level.

This method is obsolete because $SAFE is a process global state. Simply check $SAFE.

Returns:


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# File 'thread.c', line 3134

static VALUE
rb_thread_safe_level(VALUE thread)
{
    rb_warn("Thread#safe_level will be removed in Ruby 3.0");
    return UINT2NUM(GET_VM()->safe_level_);
}

#set_trace_func(proc) ⇒ Proc #set_trace_func(nil) ⇒ nil

Establishes proc on thr as the handler for tracing, or disables tracing if the parameter is nil.

See Kernel#set_trace_func.

Overloads:

  • #set_trace_func(proc) ⇒ Proc

    Returns:

  • #set_trace_func(nil) ⇒ nil

    Returns:

    • (nil)

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# File 'vm_trace.c', line 571

static VALUE
thread_set_trace_func_m(VALUE target_thread, VALUE trace)
{
    rb_execution_context_t *ec = GET_EC();
    rb_thread_t *target_th = rb_thread_ptr(target_thread);

    rb_threadptr_remove_event_hook(ec, target_th, call_trace_func, Qundef);

    if (NIL_P(trace)) {
	return Qnil;
    }
    else {
	thread_add_trace_func(ec, target_th, trace);
	return trace;
    }
}

#statusString, ...

Returns the status of thr.

"sleep"

Returned if this thread is sleeping or waiting on I/O

"run"

When this thread is executing

"aborting"

If this thread is aborting

false

When this thread is terminated normally

nil

If terminated with an exception.

a = Thread.new { raise("die now") }
b = Thread.new { Thread.stop }
c = Thread.new { Thread.exit }
d = Thread.new { sleep }
d.kill                  #=> #<Thread:0x401b3678 aborting>
a.status                #=> nil
b.status                #=> "sleep"
c.status                #=> false
d.status                #=> "aborting"
Thread.current.status   #=> "run"

See also the instance methods #alive? and #stop?

Returns:


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# File 'thread.c', line 3048

static VALUE
rb_thread_status(VALUE thread)
{
    rb_thread_t *target_th = rb_thread_ptr(thread);

    if (rb_threadptr_dead(target_th)) {
	if (!NIL_P(target_th->ec->errinfo) &&
	    !FIXNUM_P(target_th->ec->errinfo)) {
	    return Qnil;
	}
	else {
	    return Qfalse;
	}
    }
    else {
	return rb_str_new2(thread_status_name(target_th, FALSE));
    }
}

#stop?Boolean

Returns true if thr is dead or sleeping.

a = Thread.new { Thread.stop }
b = Thread.current
a.stop?   #=> true
b.stop?   #=> false

See also #alive? and #status.

Returns:

  • (Boolean)

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# File 'thread.c', line 3107

static VALUE
rb_thread_stop_p(VALUE thread)
{
    rb_thread_t *th = rb_thread_ptr(thread);

    if (rb_threadptr_dead(th)) {
	return Qtrue;
    }
    else if (th->status == THREAD_STOPPED ||
	     th->status == THREAD_STOPPED_FOREVER) {
	return Qtrue;
    }
    else {
	return Qfalse;
    }
}

#exitObject #killObject #terminateObject

Terminates thr and schedules another thread to be run, returning the terminated Thread. If this is the main thread, or the last thread, exits the process.


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# File 'thread.c', line 2466

VALUE
rb_thread_kill(VALUE thread)
{
    rb_thread_t *th = rb_thread_ptr(thread);

    if (th->to_kill || th->status == THREAD_KILLED) {
	return thread;
    }
    if (th == th->vm->main_thread) {
	rb_exit(EXIT_SUCCESS);
    }

    thread_debug("rb_thread_kill: %p (%"PRI_THREAD_ID")\n", (void *)th, thread_id_str(th));

    if (th == GET_THREAD()) {
	/* kill myself immediately */
	rb_threadptr_to_kill(th);
    }
    else {
	threadptr_check_pending_interrupt_queue(th);
	rb_threadptr_pending_interrupt_enque(th, eKillSignal);
	rb_threadptr_interrupt(th);
    }
    return thread;
}

#thread_variable?(key) ⇒ Boolean

Returns true if the given string (or symbol) exists as a thread-local variable.

me = Thread.current
me.thread_variable_set(:oliver, "a")
me.thread_variable?(:oliver)    #=> true
me.thread_variable?(:stanley)   #=> false

Note that these are not fiber local variables. Please see Thread#[] and Thread#thread_variable_get for more details.

Returns:

  • (Boolean)

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# File 'thread.c', line 3600

static VALUE
rb_thread_variable_p(VALUE thread, VALUE key)
{
    VALUE locals;
    ID id = rb_check_id(&key);

    if (!id) return Qfalse;

    if (LIKELY(!THREAD_LOCAL_STORAGE_INITIALISED_P(thread))) {
        return Qfalse;
    }
    locals = rb_thread_local_storage(thread);

    if (rb_hash_lookup(locals, ID2SYM(id)) != Qnil) {
        return Qtrue;
    }
    else {
        return Qfalse;
    }

    return Qfalse;
}

#thread_variable_get(key) ⇒ Object?

Returns the value of a thread local variable that has been set. Note that these are different than fiber local values. For fiber local values, please see Thread#[] and Thread#[]=.

Thread local values are carried along with threads, and do not respect fibers. For example:

Thread.new {
  Thread.current.thread_variable_set("foo", "bar") # set a thread local
  Thread.current["foo"] = "bar"                    # set a fiber local

  Fiber.new {
    Fiber.yield [
      Thread.current.thread_variable_get("foo"), # get the thread local
      Thread.current["foo"],                     # get the fiber local
    ]
  }.resume
}.join.value # => ['bar', nil]

The value “bar” is returned for the thread local, where nil is returned for the fiber local. The fiber is executed in the same thread, so the thread local values are available.

Returns:


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# File 'thread.c', line 3441

static VALUE
rb_thread_variable_get(VALUE thread, VALUE key)
{
    VALUE locals;

    if (LIKELY(!THREAD_LOCAL_STORAGE_INITIALISED_P(thread))) {
        return Qnil;
    }
    locals = rb_thread_local_storage(thread);
    return rb_hash_aref(locals, rb_to_symbol(key));
}

#thread_variable_set(key, value) ⇒ Object

Sets a thread local with key to value. Note that these are local to threads, and not to fibers. Please see Thread#thread_variable_get and Thread#[] for more information.


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# File 'thread.c', line 3462

static VALUE
rb_thread_variable_set(VALUE thread, VALUE id, VALUE val)
{
    VALUE locals;

    if (OBJ_FROZEN(thread)) {
        rb_frozen_error_raise(thread, "can't modify frozen thread locals");
    }

    locals = rb_thread_local_storage(thread);
    return rb_hash_aset(locals, rb_to_symbol(id), val);
}

#thread_variablesArray

Returns an array of the names of the thread-local variables (as Symbols).

thr = Thread.new do
  Thread.current.thread_variable_set(:cat, 'meow')
  Thread.current.thread_variable_set("dog", 'woof')
end
thr.join               #=> #<Thread:0x401b3f10 dead>
thr.thread_variables   #=> [:dog, :cat]

Note that these are not fiber local variables. Please see Thread#[] and Thread#thread_variable_get for more details.

Returns:


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# File 'thread.c', line 3568

static VALUE
rb_thread_variables(VALUE thread)
{
    VALUE locals;
    VALUE ary;

    ary = rb_ary_new();
    if (LIKELY(!THREAD_LOCAL_STORAGE_INITIALISED_P(thread))) {
        return ary;
    }
    locals = rb_thread_local_storage(thread);
    rb_hash_foreach(locals, keys_i, ary);

    return ary;
}

#to_sString Also known as: inspect

Dump the name, id, and status of thr to a string.

Returns:


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# File 'thread.c', line 3191

static VALUE
rb_thread_to_s(VALUE thread)
{
    VALUE cname = rb_class_path(rb_obj_class(thread));
    rb_thread_t *target_th = rb_thread_ptr(thread);
    const char *status;
    VALUE str, loc;

    status = thread_status_name(target_th, TRUE);
    str = rb_sprintf("#<%"PRIsVALUE":%p", cname, (void *)thread);
    if (!NIL_P(target_th->name)) {
        rb_str_catf(str, "@%"PRIsVALUE, target_th->name);
    }
    if ((loc = threadptr_invoke_proc_location(target_th)) != Qnil) {
        rb_str_catf(str, " %"PRIsVALUE":%"PRIsVALUE,
                    RARRAY_AREF(loc, 0), RARRAY_AREF(loc, 1));
        rb_gc_force_recycle(loc);
    }
    rb_str_catf(str, " %s>", status);

    return str;
}

#valueObject

Waits for thr to complete, using #join, and returns its value or raises the exception which terminated the thread.

a = Thread.new { 2 + 2 }
a.value   #=> 4

b = Thread.new { raise 'something went wrong' }
b.value   #=> RuntimeError: something went wrong

Returns:


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# File 'thread.c', line 1184

static VALUE
thread_value(VALUE self)
{
    rb_thread_t *th = rb_thread_ptr(self);
    thread_join(th, 0);
    return th->value;
}

#wakeupObject

Marks a given thread as eligible for scheduling, however it may still remain blocked on I/O.

Note: This does not invoke the scheduler, see #run for more information.

c = Thread.new { Thread.stop; puts "hey!" }
sleep 0.1 while c.status!='sleep'
c.wakeup
c.join#=> "hey!"


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# File 'thread.c', line 2560

VALUE
rb_thread_wakeup(VALUE thread)
{
    if (!RTEST(rb_thread_wakeup_alive(thread))) {
	rb_raise(rb_eThreadError, "killed thread");
    }
    return thread;
}