You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: cache_lock.rs
    path of file: ./repos/cargo/src/cargo/util
    
    the code of the file until where you have to start completion: //! Support for locking the package and index caches.
//!
//! This implements locking on the package and index caches (source files,
//! `.crate` files, and index caches) to coordinate when multiple cargos are
//! running at the same time.
//!
//! ## Usage
//!
//! There is a global [`CacheLocker`] held inside cargo's venerable
//! [`GlobalContext`]. The `CacheLocker` manages creating and tracking the locks
//! being held. There are methods on
    
    fn lock_shared_blocking(&mut self, gctx: &GlobalContext, description: &'static str) {
        if self.count == 0 {
            self.is_exclusive = false;
            self.lock = match gctx
                .home()
                .open_ro_shared_create(self.filename, gctx, description)
            {
                Ok(lock) => Some(lock),
                Err(e) => {
                    // There is no error here because locking is mostly a
                    // best-effort attempt. If cargo home is read-only, we don't
                    // want to fail just because we couldn't create the lock file.
                    tracing::warn!("failed to acquire cache lock {}: {e:?}", self.filename);
                    None
                }
            };
        }
        self.increment();
    }