* Defensive programming against POSIX locking idiocy.

* Simplified realiseSlice().
This commit is contained in:
Eelco Dolstra 2003-08-01 15:06:23 +00:00
parent 545145cd58
commit d99d04e644
3 changed files with 18 additions and 25 deletions

View file

@ -240,35 +240,10 @@ void realiseSlice(const FSId & id, FSIdSet pending)
if (fs.type != FState::fsSlice)
throw Error(format("expected slice in %1%") % (string) id);
/* Perhaps all paths already contain the right id? */
bool missing = false;
for (SliceElems::const_iterator i = fs.slice.elems.begin();
i != fs.slice.elems.end(); i++)
{
SliceElem elem = *i;
string id;
if (!nixDB.queryString(noTxn, dbPath2Id, elem.path, id)) {
if (pathExists(elem.path))
throw Error(format("path `%1%' obstructed") % elem.path);
missing = true;
break;
}
if (parseHash(id) != elem.id)
throw Error(format("path `%1%' obstructed") % elem.path);
}
if (!missing) {
debug(format("already installed"));
return;
}
/* For each element, expand its id at its path. */
for (SliceElems::const_iterator i = fs.slice.elems.begin();
i != fs.slice.elems.end(); i++)
{
SliceElem elem = *i;
debug(format("expanding %1% in `%2%'") % (string) elem.id % elem.path);
expandId(elem.id, elem.path, "/", pending);
}
}

View file

@ -3,6 +3,14 @@
#include "pathlocks.hh"
/* This enables us to check whether are not already holding a lock on
a file ourselves. POSIX locks (fcntl) suck in this respect: if we
close a descriptor, the previous lock will be closed as well. And
there is no way to query whether we already have a lock (F_GETLK
only works on locks held by other processes). */
static StringSet lockedPaths; /* !!! not thread-safe */
PathLocks::PathLocks(const Strings & _paths)
{
/* Note that `fds' is built incrementally so that the destructor
@ -19,6 +27,9 @@ PathLocks::PathLocks(const Strings & _paths)
string lockPath = path + ".lock";
debug(format("locking path `%1%'") % path);
if (lockedPaths.find(lockPath) != lockedPaths.end())
throw Error(format("already holding lock on `%1%'") % lockPath);
/* Open/create the lock file. */
int fd = open(lockPath.c_str(), O_WRONLY | O_CREAT, 0666);
@ -26,6 +37,7 @@ PathLocks::PathLocks(const Strings & _paths)
throw SysError(format("opening lock file `%1%'") % lockPath);
fds.push_back(fd);
this->paths.push_back(lockPath);
/* Lock it. */
struct flock lock;
@ -37,6 +49,8 @@ PathLocks::PathLocks(const Strings & _paths)
while (fcntl(fd, F_SETLKW, &lock) == -1)
if (errno != EINTR)
throw SysError(format("acquiring lock on `%1%'") % lockPath);
lockedPaths.insert(lockPath);
}
}
@ -45,4 +59,7 @@ PathLocks::~PathLocks()
{
for (list<int>::iterator i = fds.begin(); i != fds.end(); i++)
close(*i);
for (Strings::iterator i = paths.begin(); i != paths.end(); i++)
lockedPaths.erase(*i);
}

View file

@ -8,6 +8,7 @@ class PathLocks
{
private:
list<int> fds;
Strings paths;
public:
PathLocks(const Strings & _paths);