.

wcfs/client/wcfs.cpp

@@ -45,6 +45,9 @@
 // Mapping     FileH
 //
 
+// XXX locking -> explain atMu + slaves and refer to "Locking" in wcfs.go
+
+
 #include "wcfs_misc.h"
 #include "wcfs.h"
 #include "wcfs_watchlink.h"
@@ -297,6 +300,9 @@ pair<FileH, error> _Conn::open(zodb::Oid foid) {
     error err;
     xerr::Contextf E("wcfs %s: conn @%s: open f<%s>", v(wconn._wc->mountpoint), v(wconn.at), v(foid));
 
+    // XXX wconn._atMu.RLock()
+    // XXX defer wconn._atMu.RUnlock()
+
     wconn._filehmu.lock();
     defer([&]() {
         wconn._filehmu.unlock();
@@ -401,6 +407,9 @@ pair<Mapping, error> _FileH::mmap(int64_t blk_start, int64_t blk_len, VMA *vma)
         panic("(blk_start + blk_len)*f.blksize overflow int64");
     int64_t start    = blk_start*f.blksize;
 
+    // XXX wconn.atMu.RLock()
+    // XXX defer wconn.atMu.RUnlock()
+
     // XXX f locking?
 
     // create memory with head/f mapping and applied pins
@@ -459,6 +468,9 @@ error _Conn::resync(zodb::Tid at) {
     xerr::Contextf E("wcfs %s: conn @%s: resync -> @%s", v(wconn._wc->mountpoint), v(wconn.at), v(at));
 
     // XXX locking
+    // wconn.atMu.Lock()
+    // defer wconn.atMu.Unlock()
+
     error err;
 
     wconn._downMu.lock();
@@ -517,7 +529,6 @@ error _Conn::resync(zodb::Tid at) {
         if (err != nil)
             return E(err);
         if (ack != "ok") {
-            // XXX unregister f from _filehtab ?
             return E(fmt::errorf("%s", v(ack)));
         }
     }
@@ -617,10 +628,9 @@ error _Mapping::unmap() {
             v(f->wconn->_wc->mountpoint), v(f->wconn->at), v(f->foid));
 
     // XXX locking
+    // XXX make sure mmap cannot be XXX
 
     error err = mm::unmap(mmap->mem_start, mmap->mem_stop - mmap->mem_start);
-    if (err != nil)
-        return E(err);
     mmap->mem_start = NULL;
     mmap->mem_stop  = NULL;
     // XXX clear other fields?
@@ -632,7 +642,7 @@ error _Mapping::unmap() {
         std::remove(f->_mmaps.begin(), f->_mmaps.end(), mmap),
         f->_mmaps.end());
 
-    return nil;
+    return E(err);
 }
 
 

wcfs/client/wcfs.h

@@ -167,14 +167,23 @@ struct WCFS {
 typedef refptr<struct _Conn> Conn;
 struct _Conn : object {
     WCFS        *_wc;
-    zodb::Tid   at;	// XXX -> under mu
     WatchLink   _wlink; // watch/receive pins for mappings created under this conn
 
+    // atMu protects .at.
+    // While it is rlocked, .at is guaranteed to stay unchanged and Conn
+    // viewing the database at particular state. .resync write-locks this and
+    // knows noone is using the connection for reading simultaneously.
+    //
+    // XXX deadlock with pinner?
+    //
+    // sync::RWMutex _atMu
+    zodb::Tid   at;
+
     // XXX kill downMu? (move under filehmu so that e.g. .open() can check downErr without race)
     sync::Mutex _downMu;
     error       _downErr; // !nil if connection is closed or no longer operational
 
-    sync::Mutex             _filehmu;
+    sync::Mutex             _filehmu;  // _atMu.W  |  _atMu.R + _filehMu
     dict<zodb::Oid, FileH>  _filehtab; // {} foid -> fileh
 
     sync::WorkGroup _pinWG;     // pin/unpin messages from wcfs are served by _pinner