SL-16024: Defend against two threads making "anonymous" WorkQueues.

Also make workqueue_test.cpp more robust.

indra/llcommon/tests/workqueue_test.cpp

@@ -103,12 +103,13 @@ namespace tut
         Shared result = data.get();
         ensure_equals("called wrong number of times", result.size(), 3);
         // postEvery() assumes you want the first call to happen right away.
-        // Inject a fake start time that's (interval) earlier than that, to
-        // make our too early/too late tests uniform for all entries.
-        result.push_front(start - interval);
-        for (size_t i = 1; i < result.size(); ++i)
+        // Pretend our start time was (interval) earlier than that, to make
+        // our too early/too late tests uniform for all entries.
+        start -= interval;
+        for (size_t i = 0; i < result.size(); ++i)
         {
-            auto diff = (result[i] - result[i-1]);
+            auto diff = result[i] - start;
+            start += interval;
             try
             {
                 ensure(STRINGIZE("call " << i << " too soon"), diff >= interval);

indra/llcommon/workqueue.cpp

@@ -17,10 +17,15 @@
 // std headers
 // external library headers
 // other Linden headers
+#include "llcoros.h"
+#include LLCOROS_MUTEX_HEADER
 #include "llerror.h"
 #include "llexception.h"
 #include "stringize.h"
 
+using Mutex = LLCoros::Mutex;
+using Lock  = LLCoros::LockType;
+
 LL::WorkQueue::WorkQueue(const std::string& name):
     super(makeName(name))
 {
@@ -83,8 +88,17 @@ std::string LL::WorkQueue::makeName(const std::string& name)
     if (! name.empty())
         return name;
 
-    static thread_local U32 discriminator = 0;
-    return STRINGIZE("WorkQueue" << discriminator++);
+    static U32 discriminator = 0;
+    static Mutex mutex;
+    U32 num;
+    {
+        // Protect discriminator from concurrent access by different threads.
+        // It can't be thread_local, else two racing threads will come up with
+        // the same name.
+        Lock lk(mutex);
+        num = discriminator++;
+    }
+    return STRINGIZE("WorkQueue" << num);
 }
 
 void LL::WorkQueue::callWork(const Queue::DataTuple& work)