# Dependency Injection

Use dependencies when:

* They can't be declared in Pydantic validation and require additional logic
* The logic depends on external resources or could block in any other way
* Other dependencies need their results (it's a sub-dependency)
* The logic can be shared by multiple endpoints to do things like error early, authentication, etc.
* They need to handle cleanup (e.g., DB sessions, file handles), using dependencies with `yield`

// reads are running.
type syncReadCloser struct {
	rc io.ReadCloser
	mu sync.Mutex
}

func (pr *syncReadCloser) Read(p []byte) (n int, err error) {
	// This ensures that Close will block until Read has completed.
	// This allows another goroutine to close the reader.
	pr.mu.Lock()
	defer pr.mu.Unlock()
	if pr.rc == nil {
		return 0, io.EOF
	}
	return pr.rc.Read(p)
}

     *
     * @param isExtended
     *            the isExtended to set
     */
    public final void setExtended(final boolean isExtended) {
        this.isExtended = isExtended;
    }

    /**
     * Gets the oplock level granted.
     *
     * @return the oplockLevel
     */
    public final byte getOplockLevel() {
        return this.oplockLevel;
    }

    /**
     * Gets the file identifier.
     *

        response.numEntries = 2;
        byte[] params = { 0x00, 0x00, 0x00, 0x00, 0x02, 0x00, 0x02, 0x00 };
        response.readParametersWireFormat(params, 0, params.length);

        // Data block: 2 entries
        byte[] data = new byte[100];
        // Entry 1: SHARE1, type 0 (Disk), remark "Remark 1"
        System.arraycopy("SHARE1".getBytes(StandardCharsets.US_ASCII), 0, data, 0, 6);
        data[14] = 0x00;

	processedReader *countUpReader

	closedMu sync.Mutex
	closer   io.ReadCloser
	closed   bool
}

func (pr *progressReader) Read(p []byte) (n int, err error) {
	// This ensures that Close will block until Read has completed.
	// This allows another goroutine to close the reader.
	pr.closedMu.Lock()
	defer pr.closedMu.Unlock()
	if pr.closed {
		return 0, errors.New("progressReader: read after Close")
	}

        val String.barExt: String
            get() = "bar"

        var Int.bazarExt: String
            get() = "bar"
            set(value) = Unit

        operator fun String.invoke(p: String, block: String.() -> Unit) = Unit

        ${""/* For Kotlin DSL, we generate sources with collection types mapped to the Kotlin ones. See `org.gradle.kotlin.dsl.internal.sharedruntime.codegen.ApiTypeProviderKt#mappedTypeStrings` */}

	    and ends at the end of the innermost containing block.</li>

	<li>The scope of a type identifier declared inside a function
	    begins at the identifier in the TypeSpec
	    and ends at the end of the innermost containing block.</li>
</ol>

<p>
An identifier declared in a block may be redeclared in an inner block.
While the identifier of the inner declaration is in scope, it denotes

   * [trailers], this doesn't block if the trailers are not immediately available, and instead
   * returns null.
   *
   * This will typically return null until [ResponseBody.source] has buffered the last byte of the
   * response body. Call `body.source().request(1024 * 1024)` to block until either that's done, or

    assertFalse(task.isDone());
    assertFalse(task.isCancelled());

    // Start the task to put it in the RUNNING state.  Have to use a separate
    // thread because the task will block on the task latch after unblocking
    // the run latch.
    exec.execute(task);
    runLatch.await();
    assertEquals(1, listenerLatch.getCount());
    assertFalse(task.isDone());
    assertFalse(task.isCancelled());

## Async vs Sync *path operations*

Use `async` *path operations* only when fully certain that the logic called inside is compatible with async and await (it's called with `await`) or that doesn't block.

```python
from fastapi import FastAPI

app = FastAPI()


# Use async def when calling async code
@app.get("/async-items/")
async def read_async_items():