Class: RecursionLock

• Inheritance
• Description
• Related information
• Class protocol
  • instance creation
• Instance protocol
  • printing & storing
  • private-initialization
  • queries
  • waiting
• Examples

Inheritance:

   Object
   |
   +--RecursionLock
      |
      +--Dolphin::Mutex

Package:

stx:libbasic

Category:

Kernel-Processes

Version:

rev: 1.35 date: 2010/02/04 09:03:44

user: stefan

file: RecursionLock.st directory: libbasic

module: stx stc-classLibrary: libbasic

Author:

Claus Gittinger

Description:

like a Semaphore for mutual exclusion, but avoids the deadlock
if a critical region is reentered by the same process again.
I.e. allows reentering the critical region IFF the current process 
is the one which did the original locking.

WARNING:
    for now, recursionLocks are not unlocked when an image is
    restarted. You may have to recreate them to avoid a deadLock.
    (this may change in the future, but recreating a recursionLock in
     the #earlyRestart handling does not hurt)

Related information:

    Semaphore
    Process
    ProcessorScheduler

Class protocol:

 forMutualExclusion

for easy exchangability with mutual-exclusion Semaphores...

 new

Instance protocol:

 displayString

return a string to display the receiver - include the
count and user-friendly name for your convenience

 name

return the semaphores userFriendly name

 name: aString

set the semaphores userFriendly name

 initialize

 numberOfWaitingProcesses

return the number of waiting processes

 owner

return the owning processes (or nil)

 wouldBlock

Check if the resource represented by the receiver is
already in use by another Process.

 critical: aBlock

evaluate aBlock as a critical region, but do not block,
if this lock is already held by the current process.

 critical: aBlock ifBlocking: blockingBlock

like critical:, but do not block if the lock cannot be aquired.
Instead, return the value of the second argument, blockingBlock.

 critical: aBlock timeoutMs: timeoutMs ifBlocking: blockingBlock

like critical:, but do not block if the lock cannot be aquired
within timeoutMs milliseconds.
Instead, return the value of blockingBlock.

Examples:

  |lock|

  lock := RecursionLock new.
  lock critical:[
      Transcript showCR:'in lock ...'.
      lock critical:[
          Transcript showCR:'again ...'
      ]
  ]

  |lock|

  lock := Semaphore forMutualExclusion.
  lock critical:[
      Transcript showCR:'in lock ...'.
      lock critical:[
          '*** never reached - deadlock because sema is already locked ***'.
          '    (press CTRL-c and abort in the debugger)'.
          Transcript showCR:'again ...'
      ]
  ]