XrdSysXSLock Class Reference

#include <XrdSysXSLock.hh>

Collaboration diagram for XrdSysXSLock:

Public Member Functions
	XrdSysXSLock ()
	~XrdSysXSLock ()
void	Lock (const XrdSysXS_Type usage)
void	UnLock (const XrdSysXS_Type usage=xs_None)

Detailed Description

Definition at line 44 of file XrdSysXSLock.hh.

Constructor & Destructor Documentation

XrdSysXSLock()

XrdSysXSLock::XrdSysXSLock ( )

inline

Definition at line 52 of file XrdSysXSLock.hh.

                         : cur_usage(xs_None), cur_count(0), exc_wait(0),
                           shr_wait(0), toggle(0), WantShr(0), WantExc(0) {}

References xs_None.

~XrdSysXSLock()

XrdSysXSLock::~XrdSysXSLock

(

)

Definition at line 38 of file XrdSysXSLock.cc.

{
 
// Prevent usage while destroying object but make sure no one else is using it
//
   LockContext.Lock();
   if (cur_count || shr_wait || exc_wait)
      {LockContext.UnLock();
       abort();
      }
   LockContext.UnLock();
}

Member Function Documentation

Lock()

void XrdSysXSLock::Lock

(

const XrdSysXS_Type

usage

)

Definition at line 55 of file XrdSysXSLock.cc.

{
 
// Serialize access to this object
//
   LockContext.Lock();
 
// This loop continues until we can acquire the resource. We are gauranteed
// to eventually acquire it regardless of the unblocking order.
//
   while(cur_count)
        {
        // If usage is compatible with current usage get the lock right away
        //
           if (usage == xs_Shared && cur_usage == xs_Shared && !exc_wait) break;
 
        // Indicate that we are waiting
        //
           if (usage == xs_Shared) shr_wait++;
              else exc_wait++;
 
        // Usage is not compatible. We must wait for current lock mode to end
        //
           LockContext.UnLock();
           if (usage == xs_Shared) WantShr.Wait();
              else WantExc.Wait();
           LockContext.Lock();
        }
 
// We obtained the right to use this object
//
   cur_usage = usage;
   cur_count++;
   LockContext.UnLock();
}

References usage(), and xs_Shared.

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UnLock()

void XrdSysXSLock::UnLock

(

const XrdSysXS_Type

usage = xs_None

)

Definition at line 95 of file XrdSysXSLock.cc.

{
 
// Serialize access to our data
//
   LockContext.Lock();
 
// Make sure that the lock is currently being used
//
   if (!cur_count)
      {LockContext.UnLock();
       std::cerr << "XSLock: Attempt to unlock inactive lock." <<std::endl;
       throw "XSLock: unlocking inactive lock.";
      }
 
// Verify that usage is correct
//
   if (usage && cur_usage != usage)
      {LockContext.UnLock();
       std::cerr << "XSLock: Incorrect unlock usage - "
            <<  (cur_usage == xs_Shared ? "shr" : "exc") << "!="
            <<  (    usage == xs_Shared ? "shr" : "exc") << std::endl;
       throw "XSLock: invalid unlock usage specified.";
      }
 
// Unlock the current object. If no locks exist then check if we can let another
// thread use this object. The logic is tricky but we are trying to avoid
// starvation in an environment that has no thread ordering.
//
   cur_count--;
   if (!cur_count)
      if (exc_wait && (toggle || !shr_wait)) 
                             {toggle = 0; WantExc.Post(); exc_wait--;}
         else           {while(shr_wait) {WantShr.Post(); shr_wait--;}
                              toggle = 1;}
      else if (!toggle) {while(shr_wait) {WantShr.Post(); shr_wait--;}
                              toggle = 1;}
 
   LockContext.UnLock();
}

References usage(), and xs_Shared.

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The documentation for this class was generated from the following files:

• XrdSysXSLock.hh
• XrdSysXSLock.cc