Remove potential deadlock on MythSystem IO threads.

This performs finer grained locking against the file descriptor type map
in the IO handling mechanisms for MythSystem. If the read thread wakes
up and has data to process at the exact moment the external thread is
handing off a newly started child to the manager for handling, the two
may hit fdLock and MythSystemIOHandler::m_pLock from opposite
directions, deadlocking both threads.

Fixes #11066

Signed-off-by: Raymond Wagner <rwagner@mythtv.org>

mythtv/libs/libmythbase/system-unix.cpp

@@ -444,7 +444,6 @@ void MythSystemManager::append(MythSystemUnix *ms)
     m_pMap.insert(ms->m_pid, ms);
     m_mapLock.unlock();
 
-    fdLock.lock();
     if( ms->GetSetting("UseStdin") )
         writeThread->insert(ms->m_stdpipe[0], ms->GetBuffer(0));
 
@@ -453,7 +452,9 @@ void MythSystemManager::append(MythSystemUnix *ms)
         FDType_t *fdType = new FDType_t;
         fdType->ms = ms;
         fdType->type = 1;
+        fdLock.lock();
         fdMap.insert( ms->m_stdpipe[1], fdType );
+        fdLock.unlock();
         readThread->insert(ms->m_stdpipe[1], ms->GetBuffer(1));
     }
 
@@ -462,10 +463,11 @@ void MythSystemManager::append(MythSystemUnix *ms)
         FDType_t *fdType = new FDType_t;
         fdType->ms = ms;
         fdType->type = 2;
+        fdLock.lock();
         fdMap.insert( ms->m_stdpipe[2], fdType );
+        fdLock.unlock();
         readThread->insert(ms->m_stdpipe[2], ms->GetBuffer(2));
     }
-    fdLock.unlock();
 }
 
 void MythSystemManager::jumpAbort(void)

mythtv/libs/libmythbase/system-windows.cpp

@@ -402,7 +402,6 @@ void MythSystemManager::append(MythSystemWindows *ms)
     ChildListRebuild();
     m_mapLock.unlock();
 
-    fdLock.lock();
     if( ms->GetSetting("UseStdin") )
         writeThread->insert(ms->m_stdpipe[0], ms->GetBuffer(0));
 
@@ -411,7 +410,9 @@ void MythSystemManager::append(MythSystemWindows *ms)
         FDType_t *fdType = new FDType_t;
         fdType->ms = ms;
         fdType->type = 1;
+        fdLock.lock();
         fdMap.insert( ms->m_stdpipe[1], fdType );
+        fdLock.unlock();
         readThread->insert(ms->m_stdpipe[1], ms->GetBuffer(1));
     }
 
@@ -420,10 +421,11 @@ void MythSystemManager::append(MythSystemWindows *ms)
         FDType_t *fdType = new FDType_t;
         fdType->ms = ms;
         fdType->type = 2;
+        fdLock.lock();
         fdMap.insert( ms->m_stdpipe[2], fdType );
+        fdLock.unlock();
         readThread->insert(ms->m_stdpipe[2], ms->GetBuffer(2));
     }
-    fdLock.unlock();
 }
 
 void MythSystemManager::jumpAbort(void)