R/queue.R

   1 createQ <- function(filename) {
   2         dbCreate(filename, "DB1")
   3         qdb <- dbInit(filename, "DB1")
   4
   5         metaname <- paste(filename, "head", sep = ".")
   6         file.create(metaname)
   7
   8         list(qdb = qdb, meta = metaname, name = filename)
   9 }
  10
  11 initQ <- function(filename) {
  12         list(qdb = dbInit(filename, "DB1"),
  13              meta = paste(filename, "head", sep = "."),
  14              name = filename)
  15 }
  16
  17 lockFileQ <- function(dbl) {
  18         paste(dbl$name, "qlock", sep = ".")
  19 }
  20
  21 putQ <- function(dbl, vals) {
  22         if(!createLockFile(lockFileQ(dbl)))
  23                 stop("cannot create lock file")
  24         on.exit(deleteLockFile(lockFileQ(dbl)))
  25
  26         if(!is.list(vals))
  27                 vals <- as.list(vals)
  28         len <- length(vals)
  29         nextkey <- readLines(dbl$meta)
  30
  31         for(i in seq_along(vals)) {
  32                 obj <- list(value = vals[[i]], nextkey = nextkey)
  33                 key <- sha1(obj)
  34
  35                 ## These two are critical and need to be protected
  36                 writeLines(key, dbl$meta)
  37                 dbInsert(dbl$qdb, key, obj)
  38
  39                 nextkey <- key
  40         }
  41         writeLines(nextkey, dbl$meta)
  42 }
  43
  44 headQkey <- function(dbl) {
  45         with(dbl, readLines(meta))
  46 }
  47
  48 popQ <- function(dbl) {
  49         if(!createLockFile(lockFileQ(dbl)))
  50                 stop("cannot create lock file")
  51         on.exit(deleteLockFile(lockFileQ(dbl)))
  52
  53         h <- headQkey(dbl)
  54
  55         if(!length(h))
  56                 return(NULL)
  57         obj <- dbFetch(dbl$qdb, h)
  58
  59         ## These two are critical and need to be protected
  60         writeLines(obj$nextkey, meta)
  61         dbDelete(dbl$qdb, h)
  62
  63         obj$value
  64 }