diff audioDB.cpp @ 400:8c7453fb5bd9 api-inversion

Invert audioDB::power_flag / audiodb_power()

Here the exciting discovery is that the mmap(), memcpy(), munmap()
sequence is in fact not safe.  In principle an msync() call should be
inserted before unmapping for in-core changes to mmap()ed files to be
flushed to disk.

In this case we work around the problem entirely, by not mmap()ing
anything and doing everything with file descriptors.  Amusingly, that's
probably not desperately safe either, this time because we have to move
the file descriptor position (which is also a shared resource).  dup()
doesn't save us, as the duplicate file descriptor shares a file
position.

This applies also to the filling of data_buffer in the query loop, and
in fact basically any call to lseek(), which is why I'm not fixing it
now.  Solution: if you have multiple threads all acting at once on a
single database, do one audiodb_open() per thread, for now at least.

--- a/audioDB.cpp	Thu Nov 27 15:19:49 2008 +0000
+++ b/audioDB.cpp	Thu Nov 27 16:22:52 2008 +0000
@@ -771,13 +771,14 @@
 }
 
 void audioDB::power_flag(const char *dbName) {
-  forWrite = true;
-  initTables(dbName, 0);  
-  if( !(dbH->flags & O2_FLAG_LARGE_ADB ) && (dbH->length>0) ){
-    error("cannot turn on power storage for non-empty database", dbName);
+  if(!adb) {
+    if(!(adb = audiodb_open(dbName, O_RDWR))) {
+      error("Failed to open database file", dbName);
+    }
   }
-  dbH->flags |= O2_FLAG_POWER;
-  memcpy(db, dbH, O2_HEADERSIZE);
+  if(audiodb_power(adb)) {
+    error("can't turn on power flag for database", dbName);
+  }
 }
 
 void audioDB::create(const char *dbName) {
@@ -1154,20 +1155,5 @@
       audioDB::audioDB(4,argv,&apierror,mydb);
       return apierror;
   }
-
-  int audiodb_power(adb_ptr mydb){
-
-      const char *argv[5];
-      int apierror=0;
-
-      argv[0]="audioDB";
-      argv[1]="--POWER";
-      argv[2]="-d";
-      argv[3]=mydb->path;
-      argv[4]='\0';
-
-      audioDB::audioDB(4,argv,&apierror,mydb);
-      return apierror;
-  }
 }