Figure 3-7. Second part of the pseudocode for when a process ask for a latch. The three core supporting functions are depicted; fast_get, spin_get, and sleep.

Once the address of the child latch is known, the developer must also know whether the latch should be acquired in shared mode or exclusive mode. Shared mode is likely to be acquired more quickly, because multiple processes can share a latch, but only one process can acquire and hold a latch in exclusive mode. If the memory structure is only to be scanned, but not changed, then perhaps the developer can ask for the latch in shared mode. But if the memory structure is going to be altered in some way, an exclusive mode request is required.

The developer also needs to know if the latch request type is immediate or willing to wait. An immediate latch request, sometimes called a nowait request, is a single "give me the latch this instant" request. This is commonly called a fast get, and this Fast_Get function is shown in Figure 3-7.