How does the Lock interface lock objects without synchronization?

Hello!
I am reading about the Lock interface (java.util.concurrent.locks.Lock). I have checked the source code of it but I cannot understand how the Lock interface can lock an object by using Lock.lock(). I cannot see any synchronizations in ReentrantLock or its dependency classes.
So how does the locking really works when using Lock interface?

Roxxor wrote:
Hello!
I am reading about the Lock interface (java.util.concurrent.locks.Lock). I have checked the source code of it but I cannot understand how the Lock interface can lock an object by using Lock.lock(). I cannot see any synchronizations in ReentrantLock or its dependency classes.
So how does the locking really works when using Lock interface?Either it does use Java's language-level synchronization, or it uses native methods that use platform-specific native atomicity features. Or both. Those are the only possibilities.

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Message was edited by: Demo

What is the use for lock object and how to use the lock objects

Hi Guru's,
I am new to ABAP .Can you please clarify the that what is the use of lock object and how to use the loct object .what is use of the Deque & Enque function modules .

hi ,
below are some minfo about lock objects :
Lock Objects
These types of objects are used for locking the access to database records in table. This mechanism is used to enforce data integrity that is two users cannot update the same data at the same time. With lock objects you can lock table-field or whole table.
In a system where many users can access the same data, it becomes necessary to control the access to the data. In R/3 system this access control is built-in on database tables. Developers can also lock objects over table records.
To lock an object you need to call standard functions, which are automatically generated while defining the lock object in ABAP/4 dictionary. This locking system is independent of the locking mechanism used by the R/3 system. This mechanism also defines LUW i.e. Logical Unit of Work. Whenever an object is locked, either by in built locking mechanism or by function modules, it creates corresponding entry in global system table i.e. table is locked. The system automatically releases the lock at the end of transaction. The LUW starts when a lock entry is created in the system table and ends when the lock is released.
Creating Lock Objects
Lock object is an aggregated dictionary object and can be defined by using the following steps:
o From initial data dictionary screen, enter the name for the object, Click Lock object radiobutton and then click on Create. The system displays a dialog box for Maintain Lock Objects screen
o Enter short text as usual and the name for primary table.
-Save
-Select Tables option
From this screen you can:
Select secondary tables, if any, linked by foreign key relationship.
Fields for the lock objects. This option allows you to select fields for objects (R/3 system allows locking up to record level). Lock object argument are not selected by user but are imposed by the system and includes all the primary keys for the table.
1) Exclusive lock: The locked data can only be displayed or edited by a single user. A request for another exclusive lock or for a shared lock is rejected.
2) Shared lock: More than one user can access the locked data at the same time in display mode. A request for another shared lock is accepted, even if it comes from another user. An exclusive lock is rejected.
3) Exclusive but not cumulative: Exclusive locks can be requested several times from the same transaction and are processed successively. In contrast, exclusive but not cumulative locks can be called only once from the same transaction. All other lock requests are rejected.
Also, last but not the least, locking the object is logical (locking with any enqueue ) .so, you have to use the lock object while trying to access from second program .
reward if helpful ,
Regards,
Ranjita

How to use lock object? what we lock either total ztable or only record?

Hi
How to use lock object? what we lock either total ztable or only particular record?
Don't tell create lock object on se11 with E letter & acll it in program with eENQUEUE & DEQUEUE.
just tell me we will lock only particular record or total ztable?
specify with example.
Thanks.

Hi
Go to SE11, in the option 'Lock object' enter the name of your lock,
begin with 'E', suppose 'EXXXX' And create. In tab 'Tables' fill the
table name where the record you want to lock exist and select the
lock mode. Lock mode can be shared and exclusive. If 'shared',
when you lock the record, other can also read data, but can not
modify. If 'exclusive', when you lock the record, other can neither
read nor modify the record. After save and activate, you will get two
function module.'ENQUEUE_EXXXX' to lock record,
'DEQUEUE_EXXXX' to release lock on one record.
When use this function module it only lock one record at a time. It
does not lock the table.

How to create lock object?

How to create lock object,- by going to se11 i have created but when i am going to sm12 to see wheather the table is locked or not then it is showing no entries found.
Please help me how to create Lock object and see wheather thetable is lock is locked or not.
Thnks in advance

Hi venkateshwar,
Lock objects are use in SAP to avoid the inconsistancy at the time of data is being insert/change into database.
SAP Provide three type of Lock objects.
     Read Lock(Shared Locked)
protects read access to an object. The read lock allows other transactions read access but not write access to
the locked area of the table
     Write Lock(exclusive lock)
protects write access to an object. The write lock allows other transactions neither read nor write access to
the locked area of the table.
     Enhanced write lock (exclusive lock without cumulating)
works like a write lock except that the enhanced write lock also protects from further accesses from the
same transaction.
http://help.sap.com/saphelp_nw04/helpdata/en/cf/21eea5446011d189700000e8322d00/content.htm
https://forums.sdn.sap.com/click.jspa?searchID=115258&messageID=2656474
Do the following steps..
GO TO SE11
Select the radio button "Lock object"..
Give the name starts with EZ or EY..
Example: EYTEST
Press Create button..
Give the short description..
Example: Lock object for table ZTABLE..
In the tables tab..Give the table name..
Example: ZTABLE
Save and generate..
Your lock object is now created..You can see the LOCK MODULES..
In the menu ..GOTO -> LOCK MODULES..There you can see the ENQUEUE and DEQUEUE function
<b>Reward points if this helps.
Manish</b>

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Saw this solution on another post about an iPad in a school environment. Might work on your iPad so you won't lose everything.
~~~~~~~~~~~~~
‘iPad is disabled’ fix without resetting using iTunes
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2. Open iTunes with the iPad disconnected.
3. Connect the iPad to the computer and wait for it to show up in the devices section in iTunes.
4. Click on the iPad name when it appears and you will be given the option to restore a backup or setup as a new iPad (since it is locked).
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7. When the backup cancels, it immediately starts syncing – cancel this as well using the same small x in the iTunes status window.
8. The first stage in the restore process unlocks the iPad, you are basically just cancelling out the restore process as soon as it reactivates the iPad.
If done correctly, you will experience no data loss and the result will be a reactivated iPad. I have now tried this with about 5 iPads that were locked identically by students and each time it worked like a charm.
~~~~~~~~~~~~~
Try it and good luck. You have nothing more to lose if it doesn't work for you.
 Cheers, Tom

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If you are updating Z-fields then you need to create a lock entry, before you use call transaction.
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CALL FUNCTION 'ENQUEUE_REPORT'
EXPORTING
gclient                     = sy-mandt
gname                       = 'RCTMV'         "Table Name
GTARG                       = ' '
GUNAME                      = SY-UNAME
IMPORTING
number                      =
SUBRC                       =
TABLES
    enq                         = lt_seqg3
EXCEPTIONS
   communication_failure       = 1
   system_failure              = 2
   OTHERS                      = 3

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How does the Lock interface lock objects without synchronization?

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