Pathlocks Implementation for Windows (#10586)

Based on Volth's original port.

Co-authored-by: volth <volth@volth.com>

src/build-remote/build-remote.cc

@@ -22,7 +22,6 @@
 #include "experimental-features.hh"
 
 using namespace nix;
-using namespace nix::unix;
 using std::cin;
 
 static void handleAlarm(int sig) {

src/libstore/pathlocks.hh

@@ -5,10 +5,26 @@
 
 namespace nix {
 
+/**
+ * Open (possibly create) a lock file and return the file descriptor.
+ * -1 is returned if create is false and the lock could not be opened
+ * because it doesn't exist.  Any other error throws an exception.
+ */
+AutoCloseFD openLockFile(const Path & path, bool create);
+
+/**
+ * Delete an open lock file.
+ */
+void deleteLockFile(const Path & path, Descriptor desc);
+
+enum LockType { ltRead, ltWrite, ltNone };
+
+bool lockFile(Descriptor desc, LockType lockType, bool wait);
+
 class PathLocks
 {
 private:
-    typedef std::pair<int, Path> FDPair;
+    typedef std::pair<Descriptor, Path> FDPair;
     std::list<FDPair> fds;
     bool deletePaths;
 
@@ -24,6 +40,18 @@ public:
     void setDeletion(bool deletePaths);
 };
 
-}
+struct FdLock
+{
+    Descriptor desc;
+    bool acquired = false;
 
-#include "pathlocks-impl.hh"
+    FdLock(Descriptor desc, LockType lockType, bool wait, std::string_view waitMsg);
+
+    ~FdLock()
+    {
+        if (acquired)
+            lockFile(desc, ltNone, false);
+    }
+};
+
+}

src/libstore/unix/lock.cc

@@ -9,8 +9,6 @@
 
 namespace nix {
 
-using namespace nix::unix;
-
 #if __linux__
 
 static std::vector<gid_t> get_group_list(const char *username, gid_t group_id)

src/libstore/unix/pathlocks-impl.hh

@@ -1,38 +0,0 @@
-#pragma once
-///@file
-
-#include "file-descriptor.hh"
-
-namespace nix::unix {
-
-/**
- * Open (possibly create) a lock file and return the file descriptor.
- * -1 is returned if create is false and the lock could not be opened
- * because it doesn't exist.  Any other error throws an exception.
- */
-AutoCloseFD openLockFile(const Path & path, bool create);
-
-/**
- * Delete an open lock file.
- */
-void deleteLockFile(const Path & path, int fd);
-
-enum LockType { ltRead, ltWrite, ltNone };
-
-bool lockFile(int fd, LockType lockType, bool wait);
-
-struct FdLock
-{
-    int fd;
-    bool acquired = false;
-
-    FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg);
-
-    ~FdLock()
-    {
-        if (acquired)
-            lockFile(fd, ltNone, false);
-    }
-};
-
-}

src/libstore/unix/pathlocks.cc

@@ -14,9 +14,7 @@
 
 namespace nix {
 
-using namespace nix::unix;
+AutoCloseFD openLockFile(const Path & path, bool create)
-
-AutoCloseFD unix::openLockFile(const Path & path, bool create)
 {
     AutoCloseFD fd;
 
@@ -28,20 +26,20 @@ AutoCloseFD unix::openLockFile(const Path & path, bool create)
 }
 
 
-void unix::deleteLockFile(const Path & path, int fd)
+void deleteLockFile(const Path & path, Descriptor desc)
 {
     /* Get rid of the lock file.  Have to be careful not to introduce
        races.  Write a (meaningless) token to the file to indicate to
        other processes waiting on this lock that the lock is stale
        (deleted). */
     unlink(path.c_str());
-    writeFull(fd, "d");
+    writeFull(desc, "d");
     /* Note that the result of unlink() is ignored; removing the lock
        file is an optimisation, not a necessity. */
 }
 
 
-bool unix::lockFile(int fd, LockType lockType, bool wait)
+bool lockFile(Descriptor desc, LockType lockType, bool wait)
 {
     int type;
     if (lockType == ltRead) type = LOCK_SH;
@@ -50,7 +48,7 @@ bool unix::lockFile(int fd, LockType lockType, bool wait)
     else abort();
 
     if (wait) {
-        while (flock(fd, type) != 0) {
+        while (flock(desc, type) != 0) {
             checkInterrupt();
             if (errno != EINTR)
                 throw SysError("acquiring/releasing lock");
@@ -58,7 +56,7 @@ bool unix::lockFile(int fd, LockType lockType, bool wait)
                 return false;
         }
     } else {
-        while (flock(fd, type | LOCK_NB) != 0) {
+        while (flock(desc, type | LOCK_NB) != 0) {
             checkInterrupt();
             if (errno == EWOULDBLOCK) return false;
             if (errno != EINTR)
@@ -149,16 +147,16 @@ void PathLocks::unlock()
 }
 
 
-FdLock::FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg)
+FdLock::FdLock(Descriptor desc, LockType lockType, bool wait, std::string_view waitMsg)
-    : fd(fd)
+    : desc(desc)
 {
     if (wait) {
-        if (!lockFile(fd, lockType, false)) {
+        if (!lockFile(desc, lockType, false)) {
             printInfo("%s", waitMsg);
-            acquired = lockFile(fd, lockType, true);
+            acquired = lockFile(desc, lockType, true);
         }
     } else
-        acquired = lockFile(fd, lockType, false);
+        acquired = lockFile(desc, lockType, false);
 }
 
 

src/libstore/windows/pathlocks-impl.hh

@@ -1,2 +0,0 @@
-#pragma once
-///@file Needed because Unix-specific counterpart

src/libstore/windows/pathlocks.cc

@@ -1,16 +1,149 @@
 #include "logging.hh"
 #include "pathlocks.hh"
+#include "signals.hh"
+#include "util.hh"
+#include <errhandlingapi.h>
+#include <fileapi.h>
+#include <windows.h>
+#include "windows-error.hh"
 
 namespace nix {
 
-bool PathLocks::lockPaths(const PathSet & _paths, const std::string & waitMsg, bool wait)
+void deleteLockFile(const Path & path, Descriptor desc)
 {
-    return true;
+
+    int exit = DeleteFileA(path.c_str());
+    if (exit == 0)
+        warn("%s: &s", path, std::to_string(GetLastError()));
 }
 
 void PathLocks::unlock()
 {
-    warn("PathLocks::unlock: not yet implemented");
+    for (auto & i : fds) {
+        if (deletePaths)
+            deleteLockFile(i.second, i.first);
+
+        if (CloseHandle(i.first) == -1)
+            printError("error (ignored): cannot close lock file on '%1%'", i.second);
+
+        debug("lock released on '%1%'", i.second);
+    }
+
+    fds.clear();
+}
+
+AutoCloseFD openLockFile(const Path & path, bool create)
+{
+    AutoCloseFD desc = CreateFileA(
+        path.c_str(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL,
+        create ? OPEN_ALWAYS : OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL | FILE_FLAG_POSIX_SEMANTICS, NULL);
+    if (desc.get() == INVALID_HANDLE_VALUE)
+        warn("%s: %s", path, std::to_string(GetLastError()));
+
+    return desc;
+}
+
+bool lockFile(Descriptor desc, LockType lockType, bool wait)
+{
+    switch (lockType) {
+    case ltNone: {
+        OVERLAPPED ov = {0};
+        if (!UnlockFileEx(desc, 0, 2, 0, &ov)) {
+            WinError winError("Failed to unlock file desc %s", desc);
+            throw winError;
+        }
+        return true;
+    }
+    case ltRead: {
+        OVERLAPPED ov = {0};
+        if (!LockFileEx(desc, wait ? 0 : LOCKFILE_FAIL_IMMEDIATELY, 0, 1, 0, &ov)) {
+            WinError winError("Failed to lock file desc %s", desc);
+            if (winError.lastError == ERROR_LOCK_VIOLATION)
+                return false;
+            throw winError;
+        }
+
+        ov.Offset = 1;
+        if (!UnlockFileEx(desc, 0, 1, 0, &ov)) {
+            WinError winError("Failed to unlock file desc %s", desc);
+            if (winError.lastError != ERROR_NOT_LOCKED)
+                throw winError;
+        }
+        return true;
+    }
+    case ltWrite: {
+        OVERLAPPED ov = {0};
+        ov.Offset = 1;
+        if (!LockFileEx(desc, LOCKFILE_EXCLUSIVE_LOCK | (wait ? 0 : LOCKFILE_FAIL_IMMEDIATELY), 0, 1, 0, &ov)) {
+            WinError winError("Failed to lock file desc %s", desc);
+            if (winError.lastError == ERROR_LOCK_VIOLATION)
+                return false;
+            throw winError;
+        }
+
+        ov.Offset = 0;
+        if (!UnlockFileEx(desc, 0, 1, 0, &ov)) {
+            WinError winError("Failed to unlock file desc %s", desc);
+            if (winError.lastError != ERROR_NOT_LOCKED)
+                throw winError;
+        }
+        return true;
+    }
+    default:
+        assert(false);
+    }
+}
+
+bool PathLocks::lockPaths(const PathSet & paths, const std::string & waitMsg, bool wait)
+{
+    assert(fds.empty());
+
+    for (auto & path : paths) {
+        checkInterrupt();
+        Path lockPath = path + ".lock";
+        debug("locking path '%1%'", path);
+
+        AutoCloseFD fd;
+
+        while (1) {
+            fd = openLockFile(lockPath, true);
+            if (!lockFile(fd.get(), ltWrite, false)) {
+                if (wait) {
+                    if (waitMsg != "")
+                        printError(waitMsg);
+                    lockFile(fd.get(), ltWrite, true);
+                } else {
+                    unlock();
+                    return false;
+                }
+            }
+
+            debug("lock aquired on '%1%'", lockPath);
+
+            struct _stat st;
+            if (_fstat(fromDescriptorReadOnly(fd.get()), &st) == -1)
+                throw SysError("statting lock file '%1%'", lockPath);
+            if (st.st_size != 0)
+                debug("open lock file '%1%' has become stale", lockPath);
+            else
+                break;
+        }
+
+        fds.push_back(FDPair(fd.release(), lockPath));
+    }
+    return true;
+}
+
+FdLock::FdLock(Descriptor desc, LockType lockType, bool wait, std::string_view waitMsg)
+    : desc(desc)
+{
+    if (wait) {
+        if (!lockFile(desc, lockType, false)) {
+            printInfo("%s", waitMsg);
+            acquired = lockFile(desc, lockType, true);
+        }
+    } else
+        acquired = lockFile(desc, lockType, false);
 }
 
 }