It is just a standard function that can receive parameters.

It can be an `async def` or normal `def` function, **FastAPI** will know how to handle it correctly.

In this case, the task function will write to a file (simulating sending an email).

And as the write operation doesn't use `async` and `await`, we define the function with normal `def`:

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## Add the background task

			Err:  syscall.EISDIR,
		}
	}

	return &LockedFile{f}, nil
}

// TryLockedOpenFile - tries a new write lock, functionality
// it is similar to LockedOpenFile with with syscall.LOCK_EX
// mode but along with syscall.LOCK_NB such that the function
// doesn't wait forever but instead returns if it cannot
// acquire a write lock.
func TryLockedOpenFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {

   * segments, each governed by its own write lock. The segment lock is taken once for each explicit
   * write, and twice for each cache loading computation (once prior to loading the new value, and
   * once after loading completes). Much internal cache management is performed at the segment
   * granularity. For example, access queues and write queues are kept per segment when they are

from typing import Annotated

from fastapi import BackgroundTasks, Depends, FastAPI

app = FastAPI()


def write_log(message: str):
    with open("log.txt", mode="a") as log:
        log.write(message)


def get_query(background_tasks: BackgroundTasks, q: str | None = None):
    if q:
        message = f"found query: {q}\n"
        background_tasks.add_task(write_log, message)
    return q

pkg net/http/httputil, type ProxyRequest struct, In *http.Request #53002
pkg net/http/httputil, type ProxyRequest struct, Out *http.Request #53002
pkg net/http/httputil, type ReverseProxy struct, Rewrite func(*ProxyRequest) #53002
pkg net/http, method (*ResponseController) Flush() error #54136
pkg net/http, method (*ResponseController) Hijack() (net.Conn, *bufio.ReadWriter, error) #54136

    private final ByteArrayOutputStream out = new ByteArrayOutputStream();

    @Override
    protected void update(byte b) {
      out.write(b);
    }

    @Override
    protected void update(byte[] b, int off, int len) {
      out.write(b, off, len);
    }

    byte[] bytes() {
      return out.toByteArray();
    }

    void assertBytes(byte[] expected) {

    writer: DerWriter,
    value: T,
  ) {
    if (typeHint) {
      writer.typeHint = value
    }

    if (isOptional && value == defaultValue) {
      // Nothing to write!
      return
    }

    writer.write(name, tagClass, tag) {
      codec.encode(writer, value)
    }
  }

  /**
   * Returns a copy with a context tag. This should be used when the type is ambiguous on its own.

permissions:
  contents: read

jobs:
  close-issues:
    # Don't do this in forks
    if: github.repository == 'tensorflow/tensorflow'
    runs-on: ubuntu-latest
    permissions:
      issues: write
      pull-requests: write
    steps:
      - name: Awaiting response issues
        uses: actions/stale@28ca1036281a5e5922ead5184a1bbf96e5fc984e # v9.0.0
        with:

		delete(n.lockMap, resource)
	}
}

// dsync's distributed lock instance.
type distLockInstance struct {
	rwMutex *dsync.DRWMutex
	opsID   string
}

// Lock - block until write lock is taken or timeout has occurred.
func (di *distLockInstance) GetLock(ctx context.Context, timeout *dynamicTimeout) (LockContext, error) {
	lockSource := getSource(2)
	start := UTCNow()

        }

        try {
            write(uploadFile.getAbsolutePath(), form.designFile.getFileData());
            final String currentFileName = fileName;
            saveInfo(messages -> messages.addSuccessUploadDesignFile(GLOBAL, currentFileName));
        } catch (final Exception e) {
            logger.error("Failed to write an image file: {}", fileName, e);