lsst::ap::detail::BootstrapLock Struct Reference

Mutual exclusion lock suitable for initializing shared memory objects. More...

Public Member Functions
	BootstrapLock (char const *const name)
	~BootstrapLock ()

Public Attributes
char const *const	_name
int	_fd

Detailed Description

Mutual exclusion lock suitable for initializing shared memory objects.

Before standard POSIX shared memory mutexes can be used for inter-process synchronization, shared memory must be allocated and initialized. Therefore, such mutexes cannot be used to protect allocation and initialization of shared memory blocks themselves. BootstrapLock instances get around this by spinning on exclusive creation of a zero-size shared memory object.

Definition at line 88 of file ChunkManager.cc.

Constructor & Destructor Documentation

lsst::ap::detail::BootstrapLock::BootstrapLock

(

char const *const

name

)

Definition at line 98 of file ChunkManager.cc.

                                                    : _name(name), _fd(-1) {

    assert(name != 0 && name[0] == '/' && "BootstrapLock: illegal name");

    TimeSpec ts;
    ts.tv_nsec = 50000; // start off with 50usec sleep time
    int tries  = 22;
    int fd     = 0;

    while ((fd = ::shm_open(name, O_RDONLY | O_CREAT | O_EXCL, S_IRUSR | S_IRGRP | S_IROTH)) == -1) {
        if (tries == 0) {
            throw LSST_EXCEPT(ex::TimeoutError,
                (boost::format("Unable to obtain shared memory bootstrap lock %1%") % name).str());
        }
        ::nanosleep(&ts, 0);
        ts += ts; // exponential backoff
        --tries;
    }
    _fd = fd;
}

lsst::ap::detail::BootstrapLock::~BootstrapLock

(

)

Definition at line 120 of file ChunkManager.cc.

                              {
    if (_fd != -1) {
        ::close(_fd);
        ::shm_unlink(_name);
    }
}

Member Data Documentation

int lsst::ap::detail::BootstrapLock::_fd

Definition at line 91 of file ChunkManager.cc.

char const* const lsst::ap::detail::BootstrapLock::_name

Definition at line 90 of file ChunkManager.cc.

---

The documentation for this struct was generated from the following file:

• /home/lsstsw/stack/Linux64/ap/10.0+224/src/ChunkManager.cc