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

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

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@streeterd streeterd commented Mar 5, 2025 •
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github-actions bot commented Mar 5, 2025

Jira Issue: https://hpccsystems.atlassian.net//browse/HPCC-33586

Jirabot Action Result:
Workflow Transition To: Merge Pending
Updated PR

@streeterd streeterd force-pushed the HPCC-33586_Fix_double-checked_locking_pattern_for_CNamedGroupStore_in_Dali branch from 192c358 to 9f6be12 Compare March 5, 2025 13:53
@streeterd streeterd self-assigned this Mar 5, 2025
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Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.
@streeterd streeterd marked this pull request as ready for review March 5, 2025 14:05
@streeterd streeterd changed the title HPCC-33586 fix double checked locking pattern for c named group store in dali HPCC-33586 fix double checked locking pattern for CNamedGroupStore in dali Mar 11, 2025
@streeterd streeterd marked this pull request as draft March 11, 2025 10:26
@streeterd
HPCC-33586 Fix double-checked locking pattern in Dali
0928a7a 
Change DFdir to be an atomic pointer for thread safety.

Signed-off-by: Dave Streeter <[email protected]>
@streeterd
HPCC-33586 Fix double-checked locking pattern in Dali
53ebcce 
Change DFdir to be an atomic pointer for thread safety.

Signed-off-by: Dave Streeter <[email protected]>
@streeterd streeterd force-pushed the HPCC-33586_Fix_double-checked_locking_pattern_for_CNamedGroupStore_in_Dali branch from 9f6be12 to 53ebcce Compare March 11, 2025 10:50
@streeterd streeterd marked this pull request as ready for review March 11, 2025 10:51
ghalliday
ghalliday reviewed Mar 11, 2025
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dali/base/dadfs.cpp
@@ -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.

dali/base/dadfs.cpp Outdated
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.

dali/base/dadfs.cpp
@@ -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.

dali/base/dadfs.cpp
@@ -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

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Comment about closedownDFS() is inaccurate - I was only searching open documents, so missed the call.

@streeterd
HPCC-33586 Fix double-checked locking pattern in Dali
62f2415 
As per PR comments remove unnecessary CriticalSection

Signed-off-by: Dave Streeter <[email protected]>
@streeterd streeterd requested review from Copilot and ghalliday March 11, 2025 16:39
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Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.
streeterd
streeterd commented Mar 11, 2025
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dali/base/dadfs.cpp
if (e->errorCode()!=DCERR_server_closed)
throw;
e->Release();
if (groupStore.load())
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@ghalliday would it be safer to move up the groupStore release before the DFdir delete in case the DFdir delete ends up throwing an exception? Or not bother?

@streeterd streeterd changed the title HPCC-33586 fix double checked locking pattern for CNamedGroupStore in dali HPCC-33586 fix double checked locking pattern in dali Mar 12, 2025
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