AttachCurrentThread: failed to attached to polyglot context

Error message

AttachCurrentThread: failed to attached to polyglot context

What it means

Error "AttachCurrentThread: failed to attached to polyglot context" thrown in oracle/graal.

Source

Thrown at espresso/src/com.oracle.truffle.espresso.mokapot/src/mokapot.c:1963

    return NULL;
}

jint AttachCurrentThread_helper(JavaVM *vm, void **penv, void *args, jint (JNICALL *attach_method)(JavaVM *vm, void **penv, void *args)) {
    JavaVM *espressoJavaVM = (*vm)->reserved2;
    LibJavaVMIsolate *espressoIsolate = (*vm)->reserved0;
    graal_isolate_t *isolate = espressoIsolate->isolate;
    LibJavaVM *libjavavm = espressoIsolate->lib;
    graal_isolatethread_t *thread;
    if (libjavavm->attach_thread(isolate, &thread) != 0) {
        fprintf(stderr, "AttachCurrentThread: failed to attached to isolate" OS_NEWLINE_STR);
        return JNI_ERR;
    }
    // we must first attach to the polyglot context:
    // (*espressoJavaVM)->AttachCurrentThread is a NFI closure from this context
    // and only works correctly if we are attached.
    jint ret = libjavavm->Espresso_EnterContext(thread, (struct JavaVM_ *)espressoJavaVM);
    if (ret != JNI_OK) {
        fprintf(stderr, "AttachCurrentThread: failed to attached to polyglot context" OS_NEWLINE_STR);
        return ret;
    }
    ret = attach_method(espressoJavaVM, penv, args);
    if (ret != JNI_OK) {
        fprintf(stderr, "AttachCurrentThread: failed to attached to Espresso" OS_NEWLINE_STR);
        libjavavm->detach_thread(thread);
    }
    return ret;
}

jint AttachCurrentThread(JavaVM *vm, void **penv, void *args) {
    if ((*vm)->reserved1 != MOKA_LATTE) {
        fprintf(stderr, "AttachCurrentThread: not a MOKA_LATTE" OS_NEWLINE_STR);
        return JNI_ERR;
    }
    JavaVM *espressoJavaVM = (*vm)->reserved2;
    return AttachCurrentThread_helper(vm, penv, args, (*espressoJavaVM)->AttachCurrentThread);
}

View on GitHub (pinned to a66e9ccd1d)

Solutions

Fix the condition reported by the error: AttachCurrentThread: failed to attached to polyglot context
Check the throwing call site and ensure its documented preconditions (argument values, types, environment, or configuration) are satisfied before the call.

Example fix

Validate inputs and environment so that the failing condition does not occur: AttachCurrentThread: failed to attached to polyglot context

When it happens

Trigger: Thrown at espresso/src/com.oracle.truffle.espresso.mokapot/src/mokapot.c:1963 when the library encounters an invalid state.

Common situations: Occurs when a caller violates the contract guarded by this check: AttachCurrentThread: failed to attached to polyglot context

AI-assisted analysis of oracle/graal@a66e9ccd1d (2026-08-14). Data as JSON: /api/errors/ed76f43687940cdd. Report an issue: GitHub.