Create no-op Window pathlocks implementation

This keeps the call sites simple, eventually this should be filled in.

src/build-remote/build-remote.cc

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

src/libstore/gc.cc

@@ -29,6 +29,7 @@
 
 namespace nix {
 
+using namespace nix::unix;
 
 static std::string gcSocketPath = "/gc-socket/socket";
 static std::string gcRootsDir = "gcroots";

src/libstore/local-store.cc

@@ -52,6 +52,8 @@
 
 namespace nix {
 
+using namespace nix::unix;
+
 std::string LocalStoreConfig::doc()
 {
     return

src/libstore/local.mk

@@ -36,6 +36,9 @@ INCLUDE_libstore := -I $(d) -I $(d)/build
 ifdef HOST_UNIX
   INCLUDE_libstore += -I $(d)/unix
 endif
+ifdef HOST_WINDOWS
+  INCLUDE_libstore += -I $(d)/windows
+endif
 
 libstore_CXXFLAGS += \
  $(INCLUDE_libutil) $(INCLUDE_libstore) $(INCLUDE_libstore) \

src/libstore/lock.cc

@@ -9,6 +9,8 @@
 
 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/pathlocks.cc

@@ -6,69 +6,9 @@
 #include <cerrno>
 #include <cstdlib>
 
-#include <fcntl.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <sys/file.h>
-
 
 namespace nix {
 
-
-AutoCloseFD openLockFile(const Path & path, bool create)
-{
-    AutoCloseFD fd;
-
-    fd = open(path.c_str(), O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600);
-    if (!fd && (create || errno != ENOENT))
-        throw SysError("opening lock file '%1%'", path);
-
-    return fd;
-}
-
-
-void deleteLockFile(const Path & path, int fd)
-{
-    /* 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");
-    /* Note that the result of unlink() is ignored; removing the lock
-       file is an optimisation, not a necessity. */
-}
-
-
-bool lockFile(int fd, LockType lockType, bool wait)
-{
-    int type;
-    if (lockType == ltRead) type = LOCK_SH;
-    else if (lockType == ltWrite) type = LOCK_EX;
-    else if (lockType == ltNone) type = LOCK_UN;
-    else abort();
-
-    if (wait) {
-        while (flock(fd, type) != 0) {
-            checkInterrupt();
-            if (errno != EINTR)
-                throw SysError("acquiring/releasing lock");
-            else
-                return false;
-        }
-    } else {
-        while (flock(fd, type | LOCK_NB) != 0) {
-            checkInterrupt();
-            if (errno == EWOULDBLOCK) return false;
-            if (errno != EINTR)
-                throw SysError("acquiring/releasing lock");
-        }
-    }
-
-    return true;
-}
-
-
 PathLocks::PathLocks()
     : deletePaths(false)
 {
@@ -82,68 +22,6 @@ PathLocks::PathLocks(const PathSet & paths, const std::string & waitMsg)
 }
 
 
-bool PathLocks::lockPaths(const PathSet & paths,
-    const std::string & waitMsg, bool wait)
-{
-    assert(fds.empty());
-
-    /* Note that `fds' is built incrementally so that the destructor
-       will only release those locks that we have already acquired. */
-
-    /* Acquire the lock for each path in sorted order. This ensures
-       that locks are always acquired in the same order, thus
-       preventing deadlocks. */
-    for (auto & path : paths) {
-        checkInterrupt();
-        Path lockPath = path + ".lock";
-
-        debug("locking path '%1%'", path);
-
-        AutoCloseFD fd;
-
-        while (1) {
-
-            /* Open/create the lock file. */
-            fd = openLockFile(lockPath, true);
-
-            /* Acquire an exclusive lock. */
-            if (!lockFile(fd.get(), ltWrite, false)) {
-                if (wait) {
-                    if (waitMsg != "") printError(waitMsg);
-                    lockFile(fd.get(), ltWrite, true);
-                } else {
-                    /* Failed to lock this path; release all other
-                       locks. */
-                    unlock();
-                    return false;
-                }
-            }
-
-            debug("lock acquired on '%1%'", lockPath);
-
-            /* Check that the lock file hasn't become stale (i.e.,
-               hasn't been unlinked). */
-            struct stat st;
-            if (fstat(fd.get(), &st) == -1)
-                throw SysError("statting lock file '%1%'", lockPath);
-            if (st.st_size != 0)
-                /* This lock file has been unlinked, so we're holding
-                   a lock on a deleted file.  This means that other
-                   processes may create and acquire a lock on
-                   `lockPath', and proceed.  So we must retry. */
-                debug("open lock file '%1%' has become stale", lockPath);
-            else
-                break;
-        }
-
-        /* Use borrow so that the descriptor isn't closed. */
-        fds.push_back(FDPair(fd.release(), lockPath));
-    }
-
-    return true;
-}
-
-
 PathLocks::~PathLocks()
 {
     try {
@@ -154,40 +32,10 @@ PathLocks::~PathLocks()
 }
 
 
-void PathLocks::unlock()
-{
-    for (auto & i : fds) {
-        if (deletePaths) deleteLockFile(i.second, i.first);
-
-        if (close(i.first) == -1)
-            printError(
-                "error (ignored): cannot close lock file on '%1%'",
-                i.second);
-
-        debug("lock released on '%1%'", i.second);
-    }
-
-    fds.clear();
-}
-
-
 void PathLocks::setDeletion(bool deletePaths)
 {
     this->deletePaths = deletePaths;
 }
 
 
-FdLock::FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg)
-    : fd(fd)
-{
-    if (wait) {
-        if (!lockFile(fd, lockType, false)) {
-            printInfo("%s", waitMsg);
-            acquired = lockFile(fd, lockType, true);
-        }
-    } else
-        acquired = lockFile(fd, lockType, false);
-}
-
-
 }

src/libstore/pathlocks.hh

@@ -5,22 +5,6 @@
 
 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, int fd);
-
-enum LockType { ltRead, ltWrite, ltNone };
-
-bool lockFile(int fd, LockType lockType, bool wait);
-
 class PathLocks
 {
 private:
@@ -40,18 +24,6 @@ public:
     void setDeletion(bool deletePaths);
 };
 
-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);
-    }
-};
-
 }
+
+#include "pathlocks-impl.hh"

src/libstore/unix/pathlocks-impl.hh

@@ -0,0 +1,38 @@
+#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

@@ -0,0 +1,165 @@
+#include "pathlocks.hh"
+#include "util.hh"
+#include "sync.hh"
+#include "signals.hh"
+
+#include <cerrno>
+#include <cstdlib>
+
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/file.h>
+
+
+namespace nix {
+
+using namespace nix::unix;
+
+AutoCloseFD unix::openLockFile(const Path & path, bool create)
+{
+    AutoCloseFD fd;
+
+    fd = open(path.c_str(), O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600);
+    if (!fd && (create || errno != ENOENT))
+        throw SysError("opening lock file '%1%'", path);
+
+    return fd;
+}
+
+
+void unix::deleteLockFile(const Path & path, int fd)
+{
+    /* 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");
+    /* 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)
+{
+    int type;
+    if (lockType == ltRead) type = LOCK_SH;
+    else if (lockType == ltWrite) type = LOCK_EX;
+    else if (lockType == ltNone) type = LOCK_UN;
+    else abort();
+
+    if (wait) {
+        while (flock(fd, type) != 0) {
+            checkInterrupt();
+            if (errno != EINTR)
+                throw SysError("acquiring/releasing lock");
+            else
+                return false;
+        }
+    } else {
+        while (flock(fd, type | LOCK_NB) != 0) {
+            checkInterrupt();
+            if (errno == EWOULDBLOCK) return false;
+            if (errno != EINTR)
+                throw SysError("acquiring/releasing lock");
+        }
+    }
+
+    return true;
+}
+
+
+bool PathLocks::lockPaths(const PathSet & paths,
+    const std::string & waitMsg, bool wait)
+{
+    assert(fds.empty());
+
+    /* Note that `fds' is built incrementally so that the destructor
+       will only release those locks that we have already acquired. */
+
+    /* Acquire the lock for each path in sorted order. This ensures
+       that locks are always acquired in the same order, thus
+       preventing deadlocks. */
+    for (auto & path : paths) {
+        checkInterrupt();
+        Path lockPath = path + ".lock";
+
+        debug("locking path '%1%'", path);
+
+        AutoCloseFD fd;
+
+        while (1) {
+
+            /* Open/create the lock file. */
+            fd = openLockFile(lockPath, true);
+
+            /* Acquire an exclusive lock. */
+            if (!lockFile(fd.get(), ltWrite, false)) {
+                if (wait) {
+                    if (waitMsg != "") printError(waitMsg);
+                    lockFile(fd.get(), ltWrite, true);
+                } else {
+                    /* Failed to lock this path; release all other
+                       locks. */
+                    unlock();
+                    return false;
+                }
+            }
+
+            debug("lock acquired on '%1%'", lockPath);
+
+            /* Check that the lock file hasn't become stale (i.e.,
+               hasn't been unlinked). */
+            struct stat st;
+            if (fstat(fd.get(), &st) == -1)
+                throw SysError("statting lock file '%1%'", lockPath);
+            if (st.st_size != 0)
+                /* This lock file has been unlinked, so we're holding
+                   a lock on a deleted file.  This means that other
+                   processes may create and acquire a lock on
+                   `lockPath', and proceed.  So we must retry. */
+                debug("open lock file '%1%' has become stale", lockPath);
+            else
+                break;
+        }
+
+        /* Use borrow so that the descriptor isn't closed. */
+        fds.push_back(FDPair(fd.release(), lockPath));
+    }
+
+    return true;
+}
+
+
+void PathLocks::unlock()
+{
+    for (auto & i : fds) {
+        if (deletePaths) deleteLockFile(i.second, i.first);
+
+        if (close(i.first) == -1)
+            printError(
+                "error (ignored): cannot close lock file on '%1%'",
+                i.second);
+
+        debug("lock released on '%1%'", i.second);
+    }
+
+    fds.clear();
+}
+
+
+FdLock::FdLock(int fd, LockType lockType, bool wait, std::string_view waitMsg)
+    : fd(fd)
+{
+    if (wait) {
+        if (!lockFile(fd, lockType, false)) {
+            printInfo("%s", waitMsg);
+            acquired = lockFile(fd, lockType, true);
+        }
+    } else
+        acquired = lockFile(fd, lockType, false);
+}
+
+
+}

src/libstore/windows/pathlocks-impl.hh

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

src/libstore/windows/pathlocks.cc

@@ -0,0 +1,16 @@
+#include "logging.hh"
+#include "pathlocks.hh"
+
+namespace nix {
+
+bool PathLocks::lockPaths(const PathSet & _paths, const std::string & waitMsg, bool wait)
+{
+    return true;
+}
+
+void PathLocks::unlock()
+{
+    warn("PathLocks::unlock: not yet implemented");
+}
+
+}