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[XrdSys] Refactor LinuxSemaphore for more clarity
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@ljanyst
ljanyst committed Nov 22, 2013
1 parent f2961a4 commit f817eb0
Showing 1 changed file with 57 additions and 56 deletions.
113 changes: 57 additions & 56 deletions src/XrdSys/XrdSysLinuxSemaphore.hh
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Original file line number Diff line number Diff line change
Expand Up @@ -35,49 +35,6 @@
#include <exception>
#include <string>

namespace
{
//----------------------------------------------------------------------------
// Unpack the semaphore value
//----------------------------------------------------------------------------
inline void XrdSysLinuxSemaphoreUnpack( int *sourcePtr,
int &source,
int &value,
int &nwaiters )
{
source = __sync_fetch_and_add( sourcePtr, 0 );
value = source & 0x000fffff;
nwaiters = (source >> 20) & 0x00000fff;
}

//----------------------------------------------------------------------------
// Pack the semaphore value
//----------------------------------------------------------------------------
inline int XrdSysLinuxSemaphorePack( int value, int nwaiters )
{
return nwaiters << 20 | value;
}

//----------------------------------------------------------------------------
// Cancellation cleaner
//----------------------------------------------------------------------------
void XrdSysLinuxSemaphoreCleanup( void *param )
{
int *iParam = (int*)param;
int value = 0;
int val = 0;
int waiters = 0;
int newVal = 0;

do
{
XrdSysLinuxSemaphoreUnpack( iParam, value, val, waiters );
newVal = XrdSysLinuxSemaphorePack( val, --waiters );
}
while( !__sync_bool_compare_and_swap( iParam, value, newVal ) );
}
}

namespace XrdSys
{
//----------------------------------------------------------------------------
Expand Down Expand Up @@ -138,10 +95,10 @@ namespace XrdSys
//----------------------------------------------------------------------
while( 1 )
{
XrdSysLinuxSemaphoreUnpack( pValue, value, val, waiters );
Unpack( pValue, value, val, waiters );
if( val == 0 )
return 1;
newVal = XrdSysLinuxSemaphorePack( --val, waiters );
newVal = Pack( --val, waiters );
if( __sync_bool_compare_and_swap( pValue, value, newVal ) )
return 0;
}
Expand All @@ -167,12 +124,12 @@ namespace XrdSys
int waiters = 0;
int cancelType = 0;

XrdSysLinuxSemaphoreUnpack( pValue, value, val, waiters );
Unpack( pValue, value, val, waiters );

if( waiters == 0x00000fff )
if( waiters == WaitersMask )
throw LinuxSemaphoreError( "Reached maximum number of waiters" );

int newVal = XrdSysLinuxSemaphorePack( val, ++waiters );
int newVal = Pack( val, ++waiters );

//--------------------------------------------------------------------
// We have bumped the number of waiters successfuly if neither the
Expand All @@ -189,7 +146,7 @@ namespace XrdSys
{
int r = 0;

pthread_cleanup_push( XrdSysLinuxSemaphoreCleanup, pValue );
pthread_cleanup_push( Cleanup, pValue );
pthread_setcanceltype( PTHREAD_CANCEL_ASYNCHRONOUS, 0 );

r = syscall( SYS_futex, pValue, FUTEX_WAIT, newVal, 0, 0, 0 );
Expand All @@ -215,8 +172,8 @@ namespace XrdSys
//------------------------------------------------------------------
do
{
XrdSysLinuxSemaphoreUnpack( pValue, value, val, waiters );
newVal = XrdSysLinuxSemaphorePack( val, --waiters );
Unpack( pValue, value, val, waiters );
newVal = Pack( val, --waiters );
}
while( !__sync_bool_compare_and_swap( pValue, value, newVal ) );
}
Expand Down Expand Up @@ -255,12 +212,12 @@ namespace XrdSys
//----------------------------------------------------------------------
while( 1 )
{
XrdSysLinuxSemaphoreUnpack( pValue, value, val, waiters );
Unpack( pValue, value, val, waiters );

if( val == 0x000fffff )
if( val == ValueMask )
throw LinuxSemaphoreError( "Reached maximum value" );

newVal = XrdSysLinuxSemaphorePack( ++val, waiters );
newVal = Pack( ++val, waiters );
if( __sync_bool_compare_and_swap( pValue, value, newVal ) )
{
if( waiters )
Expand All @@ -276,7 +233,7 @@ namespace XrdSys
int GetValue() const
{
int value = __sync_fetch_and_add( pValue, 0 );
return value & 0x000fffff;
return value & ValueMask;
}

//------------------------------------------------------------------------
Expand All @@ -287,7 +244,7 @@ namespace XrdSys
LinuxSemaphore( int value )
{
pValue = (int *)malloc(sizeof(int));
*pValue = (value & 0x000fffff);
*pValue = (value & ValueMask);
}

//------------------------------------------------------------------------
Expand All @@ -299,6 +256,50 @@ namespace XrdSys
}

private:
static const int ValueMask = 0x000fffff;
static const int WaitersOffset = 20;
static const int WaitersMask = 0x00000fff;

//------------------------------------------------------------------------
// Unpack the semaphore value
//------------------------------------------------------------------------
static inline void Unpack( int *sourcePtr,
int &source,
int &value,
int &nwaiters )
{
source = __sync_fetch_and_add( sourcePtr, 0 );
value = source & ValueMask;
nwaiters = (source >> WaitersOffset) & WaitersMask;
}

//------------------------------------------------------------------------
// Pack the semaphore value
//------------------------------------------------------------------------
static inline int Pack( int value, int nwaiters )
{
return (nwaiters << WaitersOffset) | (value & ValueMask);
}

//------------------------------------------------------------------------
// Cancellation cleaner
//------------------------------------------------------------------------
static void Cleanup( void *param )
{
int *iParam = (int*)param;
int value = 0;
int val = 0;
int waiters = 0;
int newVal = 0;

do
{
Unpack( iParam, value, val, waiters );
newVal = Pack( val, --waiters );
}
while( !__sync_bool_compare_and_swap( iParam, value, newVal ) );
}

int *pValue;
};
};
Expand Down

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