Thread

Class

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 "Whats 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 #=> "Whats 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 "Whats 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 }

`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 { ... }
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

Any thread can raise an exception using the raise instance method, which operates similarly to Kernel#raise.

However, it’s important to note that an exception that occurs in any thread except the main thread depends on abort_on_exception. This option is false by default, meaning that any unhandled exception will cause the thread to terminate silently when waited on by either join or value. You can change this default by either abort_on_exception= true or setting $DEBUG to true.

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.

Constants

MUTEX_FOR_THREAD_EXCLUSIVE

No documentation available

Class Methods

Thread.DEBUG → num

thread.c View on GitHub

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

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

Thread.DEBUG = num

thread.c View on GitHub

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

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

Thread.abort_on_exception → true or false

thread.c View on GitHub

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

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.

Thread.abort_on_exception= boolean → true or false

thread.c View on GitHub

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

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

Thread.current → thread

thread.c View on GitHub

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

Returns the currently executing thread.

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

Thread.exclusive { block } => obj

prelude.rb View on GitHub

          
            # File tmp/rubies/ruby-2.4.10/prelude.rb, line 11
def self.exclusive
  warn "Thread.exclusive is deprecated, use Thread::Mutex", caller
  MUTEX_FOR_THREAD_EXCLUSIVE.synchronize{
    yield
  }
end

Wraps the block in a single, VM-global Mutex.synchronize, returning the value of the block. A thread executing inside the exclusive section will only block other threads which also use the Thread.exclusive mechanism.

Thread.exit → thread

thread.c View on GitHub

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

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.

Thread.start([args]*) {|args| block } → thread

Thread.fork([args]*) {|args| block } → thread

thread.c View on GitHub

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

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.

Thread.handle_interrupt(hash) { ... } → result of the block

thread.c View on GitHub

          
            static VALUE
rb_thread_s_handle_interrupt(VALUE self, VALUE mask_arg)
{
    VALUE mask;
    rb_thread_t *th = GET_THREAD();
    volatile VALUE r = Qnil;
    int state;

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

    mask = 0;
    mask_arg = rb_convert_type(mask_arg, T_HASH, "Hash", "to_hash");
    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);
    }

    TH_PUSH_TAG(th);
    if ((state = EXEC_TAG()) == 0) {
        r = rb_yield(Qnil);
    }
    TH_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);
    }

    RUBY_VM_CHECK_INTS(th);

    if (state) {
        TH_JUMP_TAG(th, state);
    }

    return r;
}

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.
}

Thread.kill(thread) → thread

thread.c View on GitHub

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

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

Thread.list → array

thread.c View on GitHub

          
            VALUE
rb_thread_list(void)
{
    VALUE ary = rb_ary_new();
    rb_vm_t *vm = GET_THREAD()->vm;
    rb_thread_t *th = 0;

    list_for_each(&vm->living_threads, th, vmlt_node) {
        switch (th->status) {
          case THREAD_RUNNABLE:
          case THREAD_STOPPED:
          case THREAD_STOPPED_FOREVER:
            rb_ary_push(ary, th->self);
          default:
            break;
        }
    }
    return ary;
}

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>

Thread.main → thread

thread.c View on GitHub

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

Returns the main thread.

Thread.new { ... } → thread

Thread.new(*args, &proc) → thread

Thread.new(*args) { |args| ... } → thread

thread.c View on GitHub

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

Thread.pass → nil

thread.c View on GitHub

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

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.

Thread.pending_interrupt?(error = nil) → true/false

thread.c View on GitHub

          
            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);
}

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

Thread.report_on_exception → true or false

thread.c View on GitHub

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

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

The default is false.

When set to true, all threads will report the exception if an exception is raised in any thread.

Thread.report_on_exception= boolean → true or false

thread.c View on GitHub

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

When set to true, all threads will report the exception if an exception is raised. Returns the new state.

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

Thread.start([args]*) {|args| block } → thread

Thread.fork([args]*) {|args| block } → thread

thread.c View on GitHub

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

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.

Thread.stop → nil

thread.c View on GitHub

          
            VALUE
rb_thread_stop(void)
{
    if (rb_thread_alone()) {
        rb_raise(rb_eThreadError,
                 "stopping only thread\n\tnote: use sleep to stop forever");
    }
    rb_thread_sleep_deadly();
    return Qnil;
}

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"

Instance Methods

thr[sym] → obj or nil

thread.c View on GitHub

          
            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);
}

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.

thr[sym] = obj → obj

thread.c View on GitHub

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

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

thr.abort_on_exception → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_abort_exc(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);
    return th->abort_on_exception ? Qtrue : Qfalse;
}

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

The default is false.

thr.abort_on_exception= boolean → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_abort_exc_set(VALUE thread, VALUE val)
{
    rb_thread_t *th;

    GetThreadPtr(thread, th);
    th->abort_on_exception = RTEST(val);
    return val;
}

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

thr.add_trace_func(proc) → proc

vm_trace.c View on GitHub

          
            static VALUE
thread_add_trace_func_m(VALUE obj, VALUE trace)
{
    rb_thread_t *th;

    GetThreadPtr(obj, th);
    thread_add_trace_func(th, trace);
    return trace;
}

Adds proc as a handler for tracing.

See Thread#set_trace_func and Kernel#set_trace_func.

thr.alive? → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_alive_p(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);

    if (rb_threadptr_dead(th))
        return Qfalse;
    return Qtrue;
}

Returns true if thr is running or sleeping.

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

thread.backtrace → array

thread.c View on GitHub

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

Returns the current backtrace of the target thread.

thread.backtrace_locations(*args) → array or nil

thread.c View on GitHub

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

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.

thr.exit → thr or nil

thread.c View on GitHub

An alias for kill

thr.group → thgrp or nil

thread.c View on GitHub

          
            VALUE
rb_thread_group(VALUE thread)
{
    rb_thread_t *th;
    VALUE group;
    GetThreadPtr(thread, th);
    group = th->thgroup;

    if (!group) {
        group = Qnil;
    }
    return group;
}

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>

thr.inspect → string

thread.c View on GitHub

          
            static VALUE
rb_thread_inspect(VALUE thread)
{
    VALUE cname = rb_class_path(rb_obj_class(thread));
    rb_thread_t *th;
    const char *status;
    VALUE str;

    GetThreadPtr(thread, th);
    status = thread_status_name(th, TRUE);
    str = rb_sprintf("#<%"PRIsVALUE":%p", cname, (void *)thread);
    if (!NIL_P(th->name)) {
        rb_str_catf(str, "@%"PRIsVALUE, th->name);
    }
    if (!th->first_func && th->first_proc) {
        VALUE loc = rb_proc_location(th->first_proc);
        if (!NIL_P(loc)) {
            const VALUE *ptr = RARRAY_CONST_PTR(loc);
            rb_str_catf(str, "@%"PRIsVALUE":%"PRIsVALUE, ptr[0], ptr[1]);
            rb_gc_force_recycle(loc);
        }
    }
    rb_str_catf(str, " %s>", status);
    OBJ_INFECT(str, thread);

    return str;
}

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

thr.join → thr

thr.join(limit) → thr

thread.c View on GitHub

          
            static VALUE
thread_join_m(int argc, VALUE *argv, VALUE self)
{
    rb_thread_t *target_th;
    double delay = DELAY_INFTY;
    VALUE limit;

    GetThreadPtr(self, target_th);

    rb_scan_args(argc, argv, "01", &limit);
    if (!NIL_P(limit)) {
        delay = rb_num2dbl(limit);
    }

    return thread_join(target_th, delay);
}

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...

thr.key?(sym) → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_key_p(VALUE self, VALUE key)
{
    rb_thread_t *th;
    ID id = rb_check_id(&key);

    GetThreadPtr(self, th);

    if (!id || !th->local_storage) {
        return Qfalse;
    }
    if (st_lookup(th->local_storage, id, 0)) {
        return Qtrue;
    }
    return Qfalse;
}

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

thr.keys → array

thread.c View on GitHub

          
            static VALUE
rb_thread_keys(VALUE self)
{
    rb_thread_t *th;
    VALUE ary = rb_ary_new();
    GetThreadPtr(self, th);

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

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]

thr.kill → thr or nil

thread.c View on GitHub

          
            VALUE
rb_thread_kill(VALUE thread)
{
    rb_thread_t *th;

    GetThreadPtr(thread, th);

    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;
}

Terminates thr 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, exits the process.

thr.name → string

thread.c View on GitHub

          
            static VALUE
rb_thread_getname(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);
    return th->name;
}

show the name of the thread.

thr.name=(name) → string

thread.c View on GitHub

          
            static VALUE
rb_thread_setname(VALUE thread, VALUE name)
{
#ifdef SET_ANOTHER_THREAD_NAME
    const char *s = "";
#endif
    rb_thread_t *th;
    GetThreadPtr(thread, th);
    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);
#ifdef SET_ANOTHER_THREAD_NAME
        s = RSTRING_PTR(name);
#endif
    }
    th->name = name;
#if defined(SET_ANOTHER_THREAD_NAME)
    if (threadptr_initialized(th)) {
        SET_ANOTHER_THREAD_NAME(th->thread_id, s);
    }
#endif
    return name;
}

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

target_thread.pending_interrupt?(error = nil) → true/false

thread.c View on GitHub

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

    GetThreadPtr(target_thread, target_th);

    if (!target_th->pending_interrupt_queue) {
        return Qfalse;
    }
    if (rb_threadptr_pending_interrupt_empty_p(target_th)) {
        return Qfalse;
    }
    else {
        if (argc == 1) {
            VALUE err;
            rb_scan_args(argc, argv, "01", &err);
            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;
            }
        }
        return Qtrue;
    }
}

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.

thr.priority → integer

thread.c View on GitHub

          
            static VALUE
rb_thread_priority(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);
    return INT2NUM(th->priority);
}

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

thr.priority= integer → thr

thread.c View on GitHub

          
            static VALUE
rb_thread_priority_set(VALUE thread, VALUE prio)
{
    rb_thread_t *th;
    int priority;
    GetThreadPtr(thread, th);


#if USE_NATIVE_THREAD_PRIORITY
    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;
    }
    th->priority = priority;
#endif
    return INT2NUM(th->priority);
}

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

thr.raise

thr.raise(string)

thr.raise(exception [, string [, array]])

thread.c View on GitHub

          
            static VALUE
thread_raise_m(int argc, VALUE *argv, VALUE self)
{
    rb_thread_t *target_th;
    rb_thread_t *th = GET_THREAD();
    GetThreadPtr(self, target_th);
    threadptr_check_pending_interrupt_queue(target_th);
    rb_threadptr_raise(target_th, argc, argv);

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

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

thr.report_on_exception → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_report_exc(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);
    return th->report_on_exception ? Qtrue : Qfalse;
}

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

The default is false.

thr.report_on_exception= boolean → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_report_exc_set(VALUE thread, VALUE val)
{
    rb_thread_t *th;

    GetThreadPtr(thread, th);
    th->report_on_exception = RTEST(val);
    return val;
}

When set to true, all threads (including the main program) will report the exception if an exception is raised in this thr.

thr.run → thr

thread.c View on GitHub

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

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

thr.safe_level → integer

thread.c View on GitHub

          
            static VALUE
rb_thread_safe_level(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);

    return INT2NUM(th->safe_level);
}

Returns the safe level in effect for thr. Setting thread-local safe levels can help when implementing sandboxes which run insecure code.

thr = Thread.new { $SAFE = 1; sleep }
Thread.current.safe_level   #=> 0
thr.safe_level              #=> 1

thr.set_trace_func(proc) → proc

thr.set_trace_func(nil) → nil

vm_trace.c View on GitHub

          
            static VALUE
thread_set_trace_func_m(VALUE obj, VALUE trace)
{
    rb_thread_t *th;

    GetThreadPtr(obj, th);
    rb_threadptr_remove_event_hook(th, call_trace_func, Qundef);

    if (NIL_P(trace)) {
        return Qnil;
    }

    thread_add_trace_func(th, trace);
    return trace;
}

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

See Kernel#set_trace_func.

thr.status → string, false or nil

thread.c View on GitHub

          
            static VALUE
rb_thread_status(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);

    if (rb_threadptr_dead(th)) {
        if (!NIL_P(th->errinfo) && !FIXNUM_P(th->errinfo)
            /* TODO */ ) {
            return Qnil;
        }
        return Qfalse;
    }
    return rb_str_new2(thread_status_name(th, FALSE));
}

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?

thr.stop? → true or false

thread.c View on GitHub

          
            static VALUE
rb_thread_stop_p(VALUE thread)
{
    rb_thread_t *th;
    GetThreadPtr(thread, th);

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

Returns true if thr is dead or sleeping.

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

thr.terminate → thr or nil

thread.c View on GitHub

An alias for kill

thr.thread_variable?(key) → true or false

thread.c View on GitHub

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

    if (!id) return Qfalse;

    locals = rb_ivar_get(thread, id_locals);

    if (!RHASH(locals)->ntbl)
        return Qfalse;

    if (st_lookup(RHASH(locals)->ntbl, ID2SYM(id), 0)) {
        return Qtrue;
    }

    return Qfalse;
}

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.

thr.thread_variable_get(key) → obj or nil

thread.c View on GitHub

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

    locals = rb_ivar_get(thread, id_locals);
    return rb_hash_aref(locals, rb_to_symbol(key));
}

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.

thr.thread_variable_set(key, value)

thread.c View on GitHub

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

    if (OBJ_FROZEN(thread)) {
        rb_error_frozen("thread locals");
    }

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

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.

thr.thread_variables → array

thread.c View on GitHub

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

    locals = rb_ivar_get(thread, id_locals);
    ary = rb_ary_new();
    rb_hash_foreach(locals, keys_i, ary);

    return ary;
}

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.

thr.value → obj

thread.c View on GitHub

          
            static VALUE
thread_value(VALUE self)
{
    rb_thread_t *th;
    GetThreadPtr(self, th);
    thread_join(th, DELAY_INFTY);
    return th->value;
}

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

thr.wakeup → thr

thread.c View on GitHub

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

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!"

Thread

Thread initialization

Thread termination

Thread status

Thread variables and scope

Fiber-local vs. Thread-local

Exception handling

Scheduling

MUTEX_FOR_THREAD_EXCLUSIVE

Thread.DEBUG → num

Thread.DEBUG = num

Thread.abort_on_exception → true or false

Thread.abort_on_exception= boolean → true or false

Thread.current → thread

Thread.exclusive { block } => obj

Thread.exit → thread

Thread.start([args]*) {|args| block } → thread

Thread.fork([args]*) {|args| block } → thread

Thread.handle_interrupt(hash) { ... } → result of the block

NOTE

Usage

Guarding from Timeout::Error

Stack control settings

Inheritance with ExceptionClass

Thread.kill(thread) → thread

Thread.list → array

Thread.main → thread

Thread.new { ... } → thread

Thread.new(*args, &proc) → thread

Thread.new(*args) { |args| ... } → thread

Thread.pass → nil

Thread.pending_interrupt?(error = nil) → true/false

Usage

Thread.report_on_exception → true or false

Thread.report_on_exception= boolean → true or false

Thread.start([args]*) {|args| block } → thread

Thread.fork([args]*) {|args| block } → thread

Thread.stop → nil

thr[sym] → obj or nil

thr[sym] = obj → obj

thr.abort_on_exception → true or false

thr.abort_on_exception= boolean → true or false

thr.add_trace_func(proc) → proc

thr.alive? → true or false

thread.backtrace → array

thread.backtrace_locations(*args) → array or nil

thr.exit → thr or nil

thr.group → thgrp or nil

thr.inspect → string

thr.join → thr

thr.join(limit) → thr

thr.key?(sym) → true or false

thr.keys → array

thr.kill → thr or nil

thr.name → string

thr.name=(name) → string

target_thread.pending_interrupt?(error = nil) → true/false

thr.priority → integer

thr.priority= integer → thr

thr.raise

thr.raise(string)

thr.raise(exception [, string [, array]])

thr.report_on_exception → true or false

thr.report_on_exception= boolean → true or false

thr.run → thr

thr.safe_level → integer

thr.set_trace_func(proc) → proc

thr.set_trace_func(nil) → nil

thr.status → string, false or nil

thr.stop? → true or false

thr.terminate → thr or nil

thr.thread_variable?(key) → true or false

thr.thread_variable_get(key) → obj or nil

thr.thread_variable_set(key, value)

thr.thread_variables → array

thr.value → obj

thr.wakeup → thr

`Thread` initialization

`Thread` termination

`Thread` status

`Thread` variables and scope

`Exception` handling

Guarding from `Timeout::Error`