Error map
ConcurrentModificationException java.util.ConcurrentModificationException
Java · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (12). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (12)
java.lang.NullPointerException
Code called a method or accessed a field on a reference that is `null`.
java.lang.UnsupportedOperationException (List.of / Arrays.asList is immutable)
Code tried to modify an immutable or fixed-size collection.
java.util.concurrent.TimeoutException
A Future.get(timeout) or async operation didn’t complete in the allowed time.
Operation cannot be fulfilled on deployments.apps "x": the object has been modified; please apply your changes to the latest version and try again
Optimistic-concurrency conflict: the object changed (new resourceVersion) between when you read it and when you tried to update i…
Go: fatal error: all goroutines are asleep - deadlock!
Every goroutine is blocked waiting (on a channel, mutex or WaitGroup), so the program can never continue.
java.lang.OutOfMemoryError: Java heap space
The JVM ran out of heap memory and garbage collection couldn’t free enough.
Optimistic lock conflict: OptimisticLockException / StaleObjectStateException / version mismatch
Someone else changed the record after you read it, so your update — based on an old version — was rejected to avoid overwriting t…
EF Core: A second operation was started on this context instance before a previous operation completed
The same DbContext was used concurrently — async calls not awaited, parallel tasks sharing a context, or a context registered as…
ERROR: could not serialize access due to concurrent update
A REPEATABLE READ/SERIALIZABLE transaction conflicted with a concurrent one and must be retried.
API Error: Too many concurrent requests (concurrency limit reached)
You have more requests in flight at once than the API allows for your key — even if your requests-per-minute rate is fine.
java.lang.InterruptedException (sleep interrupted)
A blocked thread (sleep, wait, join, queue take) was interrupted by another thread.
RuntimeError: dictionary changed size during iteration
A dict (or set) was modified while being looped over.
Two steps away (34)
System.NullReferenceException: Object reference not set to an instance of an object
Code dereferenced a variable that is `null` — the .NET equivalent of Java’s NullPointerException.
TypeError: Cannot read properties of undefined (reading 'x')
You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…
TypeError: 'NoneType' object is not subscriptable
You used `[ ]` on a value that is `None` — typically a function that returned nothing.
java.lang.ArrayIndexOutOfBoundsException: Index 5 out of bounds for length 5
Code accessed an array index outside 0 … length-1.
java.lang.ClassCastException: class A cannot be cast to class B
An object was cast to a type it isn’t.
java.lang.ArithmeticException: / by zero
Integer division or modulo by zero.
HTTP 408 Request Timeout
The server closed the connection because the client took too long to send the complete request.
HTTP 504 Gateway Timeout
A proxy or gateway waited too long for the upstream server to respond and gave up.
HTTP 409 Conflict
The request conflicts with the current state of the resource — e.g. a duplicate or an edit based on an outdated version.
HTTP 412 Precondition Failed
A conditional request header (If-Match, If-Unmodified-Since) didn’t match the current state of the resource.
API Error: Idempotency key reused with different parameters (idempotency_key_in_use)
An Idempotency-Key header was sent again with a different request body, or while the first request with that key was still runnin…
ConditionalCheckFailedException: The conditional request failed
A write’s ConditionExpression evaluated to false, so DynamoDB didn’t perform it — often exactly as designed.
HTTP 428 Precondition Required
The server requires a conditional request (If-Match / If-Unmodified-Since) to prevent lost updates, and you didn’t send one.
Conflict: AnotherOperationInProgress — Another operation is in progress on the resource
Azure is still processing a previous change on the same resource, so new operations are rejected until it finishes.
InvalidOperationException: Collection was modified; enumeration operation may not execute
A list/dictionary was changed while a foreach loop was iterating it.
Kubernetes: OOMKilled (exit code 137)
The container used more memory than its limit, and the kernel killed it.
RangeError: Maximum call stack size exceeded
A function called itself (directly or indirectly) too many times — usually infinite recursion.
PHP Fatal error: Allowed memory size of X bytes exhausted
The script tried to use more memory than PHP’s `memory_limit` allows.
Error: Too many re-renders. React limits the number of renders to prevent an infinite loop.
A state update runs during render, which triggers another render, which updates state again — forever.
Warning: A component is changing an uncontrolled input to be controlled
An input’s `value` started as `undefined` (uncontrolled) and later became a defined value (controlled), or vice versa.
java.lang.IllegalStateException
A method was called when the object wasn’t in the right state for it.
InvalidOperationException: Unable to resolve service for type 'X' while attempting to activate 'Y'
ASP.NET Core’s dependency injection container can’t build Y because one of its constructor dependencies (X) was never registered.
EF Core: The entity type 'X' requires a primary key to be defined
EF Core found an entity class without a key property it can recognise.
The instance of entity type 'X' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked
Two different objects with the same primary key were attached to one DbContext.
Deadlock found when trying to get lock; try restarting transaction
Two transactions waited on each other’s locks; the database killed one so the other could continue.
MySQL ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction
MySQL detected a deadlock between two transactions and rolled one back.
FATAL: terminating connection due to idle-in-transaction timeout
A session opened a transaction and sat idle longer than idle_in_transaction_session_timeout.
AWS: ThrottlingException / Rate exceeded
You exceeded the request rate for an AWS API; retry with exponential backoff.
HTTP 429 Too Many Requests
You’ve hit a rate limit — too many requests in a given time window. Slow down and retry later.
API Request Timed Out (ETIMEDOUT / ReadTimeout / timeout of 30000ms exceeded)
The client gave up waiting — either for the connection to open or for the response to arrive.
Main Thread Checker: UI API called on a background thread: -[UIView setNeedsLayout]
UIKit was used from a background thread; UI must only be touched on the main thread.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
TypeError: x is not iterable
for…of, spread or destructuring was used on something that isn’t an array/iterable.
ConnectionRefusedError: [Errno 111] Connection refused
Nothing is listening on the host/port Python tried to connect to.
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