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Improve the comment of util/thread_local.h

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Summary: Improve the comment of util/thread_local.h

Test Plan: n/a

Reviewers: ljin

Reviewed By: ljin

Differential Revision: https://reviews.facebook.net/D25449
This commit is contained in:
Yueh-Hsuan Chiang 2014-10-21 17:28:31 -07:00
parent 6398e6a6a5
commit e11a5e776f
1 changed files with 8 additions and 7 deletions
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15
util/thread_local.h
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@ -26,13 +26,14 @@ namespace rocksdb {
// (2) a ThreadLocalPtr is destroyed
typedef void (*UnrefHandler)(void* ptr);
// Thread local storage that only stores value of pointer type. The storage
// distinguish data coming from different thread and different ThreadLocalPtr
// instances. For example, if a regular thread_local variable A is declared
// in DBImpl, two DBImpl objects would share the same A. ThreadLocalPtr avoids
// the confliction. The total storage size equals to # of threads * # of
// ThreadLocalPtr instances. It is not efficient in terms of space, but it
// should serve most of our use cases well and keep code simple.
// ThreadLocalPtr stores only values of pointer type. Different from
// the usual thread-local-storage, ThreadLocalPtr has the ability to
// distinguish data coming from different threads and different
// ThreadLocalPtr instances. For example, if a regular thread_local
// variable A is declared in DBImpl, two DBImpl objects would share
// the same A. However, a ThreadLocalPtr that is defined under the
// scope of DBImpl can avoid such confliction. As a result, its memory
// usage would be O(# of threads * # of ThreadLocalPtr instances).
class ThreadLocalPtr {
public:
explicit ThreadLocalPtr(UnrefHandler handler = nullptr);