c8d3882cdc
parallel as possible (similar to GNU Make's `-j' switch). This is useful on SMP systems, but it is especially useful for doing builds on multiple machines. The idea is that a large derivation is initiated on one master machine, which then distributes sub-derivations to any number of slave machines. This should not happen synchronously or in lock-step, so the master must be capable of dealing with multiple parallel build jobs. We now have the infrastructure to support this. TODO: substitutes are currently broken.
127 lines
3.5 KiB
C++
127 lines
3.5 KiB
C++
#include <cerrno>
|
|
|
|
#include <sys/types.h>
|
|
#include <sys/stat.h>
|
|
#include <fcntl.h>
|
|
|
|
#include "pathlocks.hh"
|
|
|
|
|
|
bool lockFile(int fd, LockType lockType, bool wait)
|
|
{
|
|
struct flock lock;
|
|
if (lockType == ltRead) lock.l_type = F_RDLCK;
|
|
else if (lockType == ltWrite) lock.l_type = F_WRLCK;
|
|
else if (lockType == ltNone) lock.l_type = F_UNLCK;
|
|
else abort();
|
|
lock.l_whence = SEEK_SET;
|
|
lock.l_start = 0;
|
|
lock.l_len = 0; /* entire file */
|
|
|
|
if (wait) {
|
|
while (fcntl(fd, F_SETLKW, &lock) != 0) {
|
|
checkInterrupt();
|
|
if (errno != EINTR)
|
|
throw SysError(format("acquiring/releasing lock"));
|
|
}
|
|
} else {
|
|
while (fcntl(fd, F_SETLK, &lock) != 0) {
|
|
checkInterrupt();
|
|
if (errno == EACCES || errno == EAGAIN) return false;
|
|
if (errno != EINTR)
|
|
throw SysError(format("acquiring/releasing lock"));
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
|
|
/* 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()
|
|
: deletePaths(false)
|
|
{
|
|
}
|
|
|
|
|
|
PathLocks::PathLocks(const PathSet & paths)
|
|
: deletePaths(false)
|
|
{
|
|
lockPaths(paths);
|
|
}
|
|
|
|
|
|
void PathLocks::lockPaths(const PathSet & _paths)
|
|
{
|
|
/* May be called only once! */
|
|
assert(this->paths.empty());
|
|
|
|
/* Note that `fds' is built incrementally so that the destructor
|
|
will only release those locks that we have already acquired. */
|
|
|
|
/* Sort the paths. This assures that locks are always acquired in
|
|
the same order, thus preventing deadlocks. */
|
|
Paths paths(_paths.begin(), _paths.end());
|
|
paths.sort();
|
|
|
|
/* Acquire the lock for each path. */
|
|
for (Paths::iterator i = paths.begin(); i != paths.end(); i++) {
|
|
checkInterrupt();
|
|
Path path = *i;
|
|
Path lockPath = path + ".lock";
|
|
|
|
debug(format("locking path `%1%'") % path);
|
|
|
|
if (lockedPaths.find(lockPath) != lockedPaths.end()) {
|
|
debug(format("already holding lock on `%1%'") % lockPath);
|
|
continue;
|
|
}
|
|
|
|
/* Open/create the lock file. */
|
|
int fd = open(lockPath.c_str(), O_WRONLY | O_CREAT, 0666);
|
|
if (fd == -1)
|
|
throw SysError(format("opening lock file `%1%'") % lockPath);
|
|
|
|
fds.push_back(fd);
|
|
this->paths.push_back(lockPath);
|
|
|
|
/* Acquire an exclusive lock. */
|
|
lockFile(fd, ltWrite, true);
|
|
|
|
debug(format("lock acquired on `%1%'") % lockPath);
|
|
|
|
lockedPaths.insert(lockPath);
|
|
}
|
|
}
|
|
|
|
|
|
PathLocks::~PathLocks()
|
|
{
|
|
for (list<int>::iterator i = fds.begin(); i != fds.end(); i++)
|
|
if (close(*i) != 0) throw SysError("closing fd");
|
|
|
|
for (Paths::iterator i = paths.begin(); i != paths.end(); i++) {
|
|
checkInterrupt();
|
|
if (deletePaths) {
|
|
/* This is not safe in general! */
|
|
unlink(i->c_str());
|
|
/* Note that the result of unlink() is ignored; removing
|
|
the lock file is an optimisation, not a necessity. */
|
|
}
|
|
lockedPaths.erase(*i);
|
|
debug(format("lock released on `%1%'") % *i);
|
|
}
|
|
}
|
|
|
|
|
|
void PathLocks::setDeletion(bool deletePaths)
|
|
{
|
|
this->deletePaths = deletePaths;
|
|
}
|