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HPCC-33586 fix double checked locking pattern for CNamedGroupStore in dali #19585

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HPCC-33586 fix double checked locking pattern for CNamedGroupStore in dali #19585

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0928a7a
HPCC-33586 Fix double-checked locking pattern in Dali
streeterd Mar 5, 2025
53ebcce
HPCC-33586 Fix double-checked locking pattern in Dali
streeterd Mar 11, 2025
62f2415
HPCC-33586 Fix double-checked locking pattern in Dali
streeterd Mar 11, 2025
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39 changes: 19 additions & 20 deletions dali/base/dadfs.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -8239,20 +8239,22 @@ class CNamedGroupStore: implements INamedGroupStore, public CInterface

};

static CNamedGroupStore *groupStore = NULL;
static std::atomic<CNamedGroupStore *> groupStore{nullptr};
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There seems to be a mixture of fixes here. Either the variable should be atomic, or it should be accessed within a critical section. No need to do both.

static CriticalSection groupsect;

bool CNamedGroupIterator::match()
{
if (conn.get()) {
if (matchgroup.get()) {
if (!groupStore)
CLeavableCriticalBlock block3(groupsect);
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This critical section will be held over the call to dolookup. That is likely to cause extra thread contention.

If you are worried about groupStore being destroyed, a more efficient solution is to copy and link it with the critical block, and then use the linked pointer. However, see note on closedownDFS() below - in which case it can never be freed.

if (!groupStore.load())
return false;
const char *name = pe->query().queryProp("@name");
if (!name||!*name)
return false;
GroupType dummy;
Owned<IGroup> lgrp = groupStore->dolookup(name, conn, NULL, dummy);
Owned<IGroup> lgrp = groupStore.load()->dolookup(name, conn, NULL, dummy);
block3.leave();
if (lgrp) {
if (exactmatch)
return lgrp->equals(matchgroup);
Expand All @@ -8266,14 +8268,13 @@ bool CNamedGroupIterator::match()
return false;
}

INamedGroupStore &queryNamedGroupStore()
INamedGroupStore &queryNamedGroupStore()
{
if (!groupStore) {
CriticalBlock block(groupsect);
if (!groupStore)
groupStore = new CNamedGroupStore();
CriticalBlock block(groupsect);
if (!groupStore.load()) {
groupStore.store(new CNamedGroupStore());
}
return *groupStore;
return *(groupStore.load());
}

// --------------------------------------------------------
Expand Down Expand Up @@ -9204,7 +9205,7 @@ GetFileClusterNamesType CDistributedFileDirectory::getFileClusterNames(const cha
// --------------------------------------------------------


static CDistributedFileDirectory *DFdir = NULL;
static std::atomic<CDistributedFileDirectory *> DFdir{nullptr};
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Similar comments to above - either make it atomic, or protect all access within a critical section.

static CriticalSection dfdirCrit;

/**
Expand All @@ -9214,12 +9215,10 @@ static CriticalSection dfdirCrit;
*/
IDistributedFileDirectory &queryDistributedFileDirectory()
{
if (!DFdir) {
CriticalBlock block(dfdirCrit);
if (!DFdir)
DFdir = new CDistributedFileDirectory();
}
return *DFdir;
CriticalBlock block(dfdirCrit);
if (!DFdir.load())
DFdir.store(new CDistributedFileDirectory());
return *DFdir.load();
}

/**
Expand All @@ -9229,7 +9228,7 @@ void closedownDFS() // called by dacoven
{
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Is closedownDFS() ever called - I don't think so. If not the function can be deleted, avoiding the lifetime problem above.

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closedownDFS() is called from dali/base/dacoven.cpp :

image

CriticalBlock block(dfdirCrit);
try {
delete DFdir;
delete DFdir.load();
}
catch (IMP_Exception *e) {
if (e->errorCode()!=MPERR_link_closed)
Expand All @@ -9242,10 +9241,10 @@ void closedownDFS() // called by dacoven
throw;
e->Release();
}
DFdir = NULL;
DFdir.store(nullptr);
CriticalBlock block2(groupsect);
::Release(groupStore);
groupStore = NULL;
::Release(groupStore.load());
groupStore.store(nullptr);
}

class CDFPartFilter : implements IDFPartFilter, public CInterface
Expand Down
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