First implementation of plotCache

NAMESPACE

@@ -164,6 +164,7 @@ export(pageWithSidebar)
 export(paneViewer)
 export(parseQueryString)
 export(passwordInput)
+export(plotCache)
 export(plotOutput)
 export(plotPNG)
 export(pre)

R/render-plot.R

@@ -975,3 +975,77 @@ find_panel_ranges <- function(g, pixelratio, res) {
     )
   })
 }
+
+
+#' Disk-based plot cache
+#'
+#' Creates a read-through cache for plots. The plotting logic is provided as
+#' plotFunc, a function that can have any number/combination of arguments; the
+#' return value of plotCache is a function that should be used in the place of
+#' plotFunc. Each unique combination of inputs will be cached to disk in the
+#' location specified by cachePath.
+#'
+#' The invalidationExpr expression will be monitored and whenever it is
+#' invalidated, so too is the cache invalidated (the contents are erased).
+#'
+#' @param cacheId An identifier for this cache; by default, will be incorporated
+#'   into the cache directory path.
+#' @param invalidationExpr Any expression or block of code that accesses any
+#'   reactives whose invalidation should cause cache invalidation. This
+#'   typically would be an expression that indicates that the source data has
+#'   changed. Use \code{NULL} if you don't want to cause cache invalidation.
+#' @param width,height The dimensions of the plot. (Use double the user
+#'   width/height for retina/hi-dpi compatibility.)
+#' @param res The resolution of the PNG. Use 72 for normal screens, 144 for
+#'   retina/hi-dpi.
+#' @param plotFunc Plotting logic, provided as a function that takes zero or
+#'   more arguments. Don't worry about setting up a graphics device or creating
+#'   a PNG; just write to the graphics device (you must call \code{print()} on
+#'   ggplot2 objects).
+#' @param cachePath The location on disk where the cache will be stored. By
+#'   default, uses a temp directory, which is generally cleaned up during a
+#'   normal shutdown of the R process.
+#' @param invalidation.env The environment where the \code{invalidationExpr} is
+#'   evaluated.
+#' @param invalidation.quoted Is \code{invalidationExpr} expression quoted? By
+#'   default, this is FALSE. This is useful when you want to use an expression
+#'   that is stored in a variable; to do so, it must be quoted with
+#'   \code{quote()}.
+#'
+#' @export
+plotCache <- function(cacheId, invalidationExpr, width, height, res = 72,
+  plotFunc,
+  cachePath = file.path(tempdir(), cacheId),
+  invalidation.env = parent.frame(),
+  invalidation.quoted = FALSE) {
+
+  dir.create(cachePath, recursive = TRUE, mode = "0700")
+
+  if (!invalidation.quoted) {
+    invalidationExpr <- substitute(invalidationExpr)
+  }
+
+  observeEvent(invalidationExpr, event.env = invalidation.env, event.quoted = TRUE, {
+    # TODO: robustify
+    if (dir.exists(cachePath)) {
+      file.rename(cachePath, paste0(cachePath, ".gone"))
+    }
+    dir.create(cachePath, recursive = TRUE, mode = "0700")
+    unlink(paste0(cachePath, ".gone"), recursive = TRUE)
+  })
+
+  function(...) {
+    args <- list(...)
+    key <- paste0(digest::digest(args), ".png")
+    filePath <- file.path(cachePath, key)
+    if (!file.exists(filePath)) {
+      message("Cache miss")
+      plotPNG(function() {
+        do.call("plotFunc", args)
+      }, filename = filePath, width = width, height = height, res = res)
+    } else {
+      message("Cache hit")
+    }
+    filePath
+  }
+}

man/plotCache.Rd

@@ -0,0 +1,53 @@
+% Generated by roxygen2: do not edit by hand
+% Please edit documentation in R/render-plot.R
+\name{plotCache}
+\alias{plotCache}
+\title{Disk-based plot cache}
+\usage{
+plotCache(cacheId, invalidationExpr, width, height, res = 72, plotFunc,
+  cachePath = file.path(tempdir(), cacheId),
+  invalidation.env = parent.frame(), invalidation.quoted = FALSE)
+}
+\arguments{
+\item{cacheId}{An identifier for this cache; by default, will be incorporated
+into the cache directory path.}
+
+\item{invalidationExpr}{Any expression or block of code that accesses any
+reactives whose invalidation should cause cache invalidation. This
+typically would be an expression that indicates that the source data has
+changed. Use \code{NULL} if you don't want to cause cache invalidation.}
+
+\item{width, height}{The dimensions of the plot. (Use double the user
+width/height for retina/hi-dpi compatibility.)}
+
+\item{res}{The resolution of the PNG. Use 72 for normal screens, 144 for
+retina/hi-dpi.}
+
+\item{plotFunc}{Plotting logic, provided as a function that takes zero or
+more arguments. Don't worry about setting up a graphics device or creating
+a PNG; just write to the graphics device (you must call \code{print()} on
+ggplot2 objects).}
+
+\item{cachePath}{The location on disk where the cache will be stored. By
+default, uses a temp directory, which is generally cleaned up during a
+normal shutdown of the R process.}
+
+\item{invalidation.env}{The environment where the \code{invalidationExpr} is
+evaluated.}
+
+\item{invalidation.quoted}{Is \code{invalidationExpr} expression quoted? By
+default, this is FALSE. This is useful when you want to use an expression
+that is stored in a variable; to do so, it must be quoted with
+\code{quote()}.}
+}
+\description{
+Creates a read-through cache for plots. The plotting logic is provided as
+plotFunc, a function that can have any number/combination of arguments; the
+return value of plotCache is a function that should be used in the place of
+plotFunc. Each unique combination of inputs will be cached to disk in the
+location specified by cachePath.
+}
+\details{
+The invalidationExpr expression will be monitored and whenever it is
+invalidated, so too is the cache invalidated (the contents are erased).
+}