Pathlocks Implementation for Windows (#10586)

Based on Volth's original port.

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

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);
 }
 
 }