Coroutine Dumps

The Help | Diagnostic Tools | Dump Threads action creates a thread dump, which is useful when investigating freezes or deadlocks. Thread dumps include all application threads and coroutines existing at the moment of dump creation.

Coroutine Dump Format

A coroutine dump format is:

- parent coroutine header
	at stackframe
	at stackframe
	...
	- child coroutine 0 header
		at stackframe
		at stackframe
		...
		- grandchild coroutine header
			at stackframe
			at stackframe
			...
	- child coroutine 1 header
	- child coroutine 2 header
		at stackframe
		at stackframe
		...

Each coroutine entry starts with a - character. Indentation represents parent-child relationships. A coroutine entry may not include a stacktrace (see child coroutine 1 header) because it has no executable body, or it did not start executing yet.

An example coroutine header:

-[x5 of] "my task":StandaloneCoroutine{Active}, state: SUSPENDED [ComponentManager(ApplicationImpl@xxxxxxxx), Dispatchers.EDT]

Its format is as follows:

-[xN of] "name":CoroutineClass{JobState}, state: STATE [context]

`[xN of]`

A particular subtree is repeated N times (included only if N > 1).

`name`

A coroutine name.

Notable names:

ApplicationImpl@xxxxxxxx container - application coroutine.
ProjectImpl@xxxxxxxx container - project coroutine.
com.intellij.*.AClass - a coroutine bound to some specific class instance, e.g., an extension or a service. Unnamed coroutines are hard to identify, so it is recommended to add CoroutineName(someName) into a coroutine context.
(a x b) - an intersection of coroutines a and b, e.g., (ApplicationImpl@56422718 x com.example.myplugin) is an intersection of the application and a plugin scope. See also Intersection Scopes.

`CoroutineClass{JobState}`

A coroutine's toString():

CoroutineClass - a coroutine class. Notable values:
- StandaloneCoroutine and LazyStandaloneCoroutine are created by launch.
- DeferredCoroutine and LazyDeferredCoroutine are created by async.
- BlockingCoroutine is created by runBlockingCancellable().
- ProducerCoroutine is created by produce.
- ChildScope is created by childScope.
JobState - a coroutine Job's state. Possible states and transition can be found in the Job's KDoc.

`state: STATE`

A coroutine's state.

Possible states:

CREATED - a coroutine was created but not yet started.
SUSPENDED - a coroutine was executed up until the last frame in the stacktrace. This is where it was last seen running.
RUNNING - a coroutine is currently executed by a thread. Its stacktrace reflects what the coroutine is doing right now (probably blocked waiting for something, otherwise a RUNNING coroutine is rarely seen unless it’s doing CPU-intensive work).

`[context]`

A coroutine context. Context elements are separated with ,.

Notable context elements:

no parent and no name comes from the startup tracer. It should not be present in application/project coroutines and their children.
ComponentManager(ApplicationImpl@xxxxxxxx) - application or project, which serves as the coroutine parent.
BlockingEventLoop, Dispatchers.Default, Dispatchers.IO, LimitedDispatcher, Dispatchers.EDT - a coroutine dispatcher. Absence means Dispatchers.Default.
ModalityState.xxx - modality state. Absence means ModalityState.nonModal().
When EDT is in a modal state, all non-modal coroutines are suspended until the modal state ends, and EDT goes back to non-modal state as well.
Some RUNNING coroutines might block in an invokeAndWait call, which means that invokeAndWait used non-modal default modality state for one of two reasons:
- the coroutine contains the correct modality state in its context, but invokeAndWait is not aware of it
- a modal coroutine awaits another unrelated coroutine, which in turn requires non-modal EDT to complete.
Same problems can be found in regular thread dumps and blocking code, but coroutines suspend instead of blocking a thread, so it’s only possible to observe the last seen frame, which is usually enough.

Last modified: 13 June 2024