2024-11-22 03:41 AEDT
  

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IDProjectCategoryView StatusDate SubmittedLast Update
0000224mercuryBugpublic2011-10-24 11:592011-10-25 10:42
Reportercolanderman 
Assigned To 
PrioritynormalSeverityminorReproducibilityalways
StatusnewResolutionopen 
Product Version 
Target VersionFixed in Version 
Summary0000224: STM broken without --inline-compound-threshold 10 --loop-invariants
DescriptionAttached is a basic mutex implementation using STM primitives. Compile with:

mmc --parallel -O0 --inline-compound-threshold 10 --loop-invariants --rebuild stm_bug

And run. Program will behave as expected (uses 200% CPU on a multiproc platform, does not terminate).

Recompile without either one (or both) of "--inline-compound-threshold 10" or "--loop-invariants":

mmc --parallel -O0 --rebuild stm_bug

And run. Program soon terminates due to failed assertion about the state of the lock.

Behavior is identical under hlc.par grade (-H flag). Building without any optimization flags fails as well, since -O2 (the default) enables "--inline-compound-threshold 10" but not "--loop-invariants".
TagsNo tags attached.
Attached Files
  • ? file icon stm_bug.m (1,008 bytes) 2011-10-24 11:59
  • patch file icon stm.patch (762 bytes) 2011-10-25 10:41 - 
    --- mercury/runtime/mercury_stm.c	2011-05-20 00:16:55.000000000 -0400
+++ mercury-compiler-11.07-beta-2011-09-30-modded/runtime/mercury_stm.c	2011-10-24 19:37:24.723339594 -0400
@@ -264,6 +264,7 @@
 {
     MR_STM_TransLog     *current_tlog;
     MR_STM_TransRecord  *current;
+    MR_Word             value;
 
     current_tlog = tlog;
 
@@ -293,10 +294,10 @@
     ** Add an entry that indicates that it has been read and then return
     ** the value that is stored in the transaction variable.
     */
-    MR_STM_record_transaction(tlog, var, var->MR_STM_var_value,
-        var->MR_STM_var_value);
+    value = var->MR_STM_var_value;
+    MR_STM_record_transaction(tlog, var, value, value);
 
-    return var->MR_STM_var_value;
+    return value;
 }
 
 void
    patch file icon stm.patch (762 bytes) 2011-10-25 10:41 +

-Relationships
+Relationships

-Notes

~0000369

colanderman (reporter)

2011-10-24 12:16

 Note: in more complex programs I see behavior which I believe is triggered by this bug even with these optimizations enabled. I will attach a test case later.

~0000370

zs (developer)

2011-10-24 14:40

 The whole STM implementation is experimental and incomplete. It was worked on by two honours students in the past; noone is working on it currently. Bugs in it won't be fixed until we get someone else who wants to work on the STM system.

~0000373

colanderman (reporter)

2011-10-25 10:42

 There was a race condition in the STM runtime -- reading an STM variable read the physical location multiple times without a lock. Attached is a patch against CVS which fixes this.
+Notes

-Issue History
Date Modified Username Field Change
2011-10-24 11:59 colanderman New Issue
2011-10-24 11:59 colanderman File Added: stm_bug.m
2011-10-24 12:16 colanderman Note Added: 0000369
2011-10-24 14:40 zs Note Added: 0000370
2011-10-25 10:41 colanderman File Added: stm.patch
2011-10-25 10:42 colanderman Note Added: 0000373
+Issue History