ExInitializePushLock function

Description

Initializes a push lock variable.

Parameters

PushLock [Out]

Pointer to the caller-supplied storage, which must be at least the value of sizeof(EX_PUSH_LOCK), for the push lock variable to be initialized. The storage must be 4-byte aligned on 32-bit platforms, and 8-byte aligned on 64-bit platforms.

Remarks

Push locks are similar to ERESOURCE structures (also called "resources") in the following ways:

• Push locks can be used for synchronization by a set of threads.
• Push locks can be acquired for shared or exclusive access.
• Although the caller provides the storage for the push lock variable, the EX_PUSH_LOCK structure is opaque: that is, its members are reserved for system use.

Push locks offer the following advantages over ERESOURCE structures:

• When push locks are mostly acquired for shared access, they are more efficient than ERESOURCE structures.
• The storage for push locks can be allocated from paged or nonpaged pool. ERESOURCE structures must be allocated only from nonpaged pool.
• EX_PUSH_LOCK structures are much smaller than ERESOURCE structures.

Push locks have the following disadvantages when compared with ERESOURCE structures:

• The algorithm for granting exclusive access is not fair to all threads. If there is a high level of exclusive-lock contention, there is no guarantee about the order in which threads will be granted exclusive access.
• There are no support routines for determining the current owner of a push lock. (Users of ERESOURCE structures can call routines such as ExIsResourceAcquiredExclusiveLite to determine whether the current thread has exclusive access to the resource.)
• Push locks cannot be acquired recursively.

To acquire or release a push lock for exclusive access, call ExAcquirePushLockExclusive or ExReleasePushLockExclusive, respectively.

To acquire or release a push lock for shared access, call ExAcquirePushLockShared or ExReleasePushLockShared, respectively.

See also