如果先前的用户在队列中正在进行交易，那么如何确保其他用户无法完成交易？例如：
在订购系统中，require('shiny')
require('ggplot2')
require('shinyjqui')
mtcars <- as.data.table(mtcars)
max_plots <- 12;
ui <- pageWithSidebar(
headerPanel("Dynamic number of plots"),
sidebarPanel(width = 2, sliderInput("n", "Number of plots", value=5, min=1, max=max_plots),
h4('click points to see info'),
h4('select area to zoom'),
h4('Double click to unzoom')
),
mainPanel(
tags$head(
tags$style('
#my_tooltip {
position: absolute;
pointer-events:none;
width: 300px;
z-index: 100;
padding: 0;
}'),
tags$script('
$(document).ready(function() {
$("[id^=plot]").mousemove(function(e) {
$("#my_tooltip").show();
$("#my_tooltip").css({
top: (e.pageY + 5) + "px",
left: (e.pageX + 5) + "px"
});
});
});')
),
tabsetPanel(
tabPanel('fp1',
uiOutput("FP1Plotmultiplots")
),
tabPanel('clean',
uiOutput("CleanFP1multiplots")
)
),
style = 'width:1250px'
)
)
server <- function(input, output, session) {
plotlist <- c('FP1Plot', 'CleanFP1')
ranges <- reactiveValues()
# make the individual plots
observe({
lapply(1:input$n, function(i){
plotname <- paste0('FP1Plot', i)
output[[plotname]] <- renderPlot({
ggplot(mtcars, aes(wt, mpg, color = as.factor(cyl))) + geom_point() +
coord_cartesian(xlim =ranges[[paste('FP1Plot', i, 'x', sep = '')]],
ylim = ranges[[paste('FP1Plot', i, 'y', sep = '')]]
) +
theme_classic() +
theme(legend.text=element_text(size=12),
legend.title=element_blank(),
legend.position = 'bottom')
})
})
})
observe({
lapply(1:input$n, function(i){
plotname <- paste0('CleanFP1', i)
output[[plotname]] <- renderPlot({
ggplot(iris, aes(iris[ ,ncol(iris)-1], iris[ ,i], color = as.factor(Species))) + geom_point() +
coord_cartesian(xlim =ranges[[paste('CleanFP1', i, 'x', sep = '')]],
ylim = ranges[[paste('CleanFP1', i, 'y', sep = '')]]
) +
theme_classic() +
theme(legend.text=element_text(size=12),
legend.title=element_blank(),
legend.position = 'bottom')
})
})
})
# make the divs with plots and buttons etc
lapply(plotlist, function(THEPLOT) {
output[[paste(THEPLOT, 'multiplots', sep = '')]] <- renderUI({
plot_output_list <- list()
n <- input$n
n_cols <- if(n == 1) {
1
} else if (n %in% c(2,4)) {
2
} else if (n %in% c(3,5,6,9)) {
3
} else {
4
}
Pwidth <- 900/n_cols
Pheigth <- 500/ceiling(n/n_cols) # calculate number of rows
Pwidth2 <- Pwidth+40
Pheigth2 <-Pheigth+40
plot_output_list <- list();
for(i in 1:input$n) {
plot_output_list <- append(plot_output_list,list(
div(id = paste0('div', THEPLOT, i),
wellPanel(
plotOutput(paste0(THEPLOT, i),
width = Pwidth,
height = Pheigth,
hover = hoverOpts(id = paste(THEPLOT, i, "hover", sep = '_'), delay = 0)
# click = paste0(THEPLOT, i, '_click'),
# dblclick = paste0(THEPLOT, i, '_dblclick'),
# brush = brushOpts(
# id = paste0(THEPLOT, i, '_brush'),
# resetOnNew = TRUE
# )
),
style = paste('border-color:#339fff; border-width:2px; background-color: #fff; width:', Pwidth2, 'px; height:', Pheigth2, 'px', sep = '')),
style = paste('display: inline-block; margin: 2px; width:', Pwidth2, 'px; height:', Pheigth2, 'px', sep = ''))
))
}
do.call(tagList, plot_output_list)
})
})
eg <- expand.grid(plotlist, 1:max_plots)
tooltipTable <- reactive({
## attempt to make this work for the large amount of plots in my app
hovers <- as.list(sapply(c(sprintf('%s_%s', eg[,1], eg[,2])), function(key) key = eval(parse(text = paste('input$', key, '_hover', sep = ''))) ))
notNull <- sapply(hovers, Negate(is.null))
if(any(notNull)){
plotid <- names(which(notNull))
plothoverid <- paste0(plotid, "_hover")
dataset <- if(grepl('FP1Plot', plotid)) { mtcars } else { iris }
## I will add some code here based on the plot nr to grab the needed columns for the x and y data of the specific plot, since the list of x and y columns will be stored in two vectors:
## 1 vector with x parameter 1:12, and 1 for y.
## every group of plots will use the same list of selected x and y parameters
# (or if I switch to plot group specific lists, the lists will contain the group names just like the plots, so I can link them by name here)
y <- nearPoints(dataset, input[[plothoverid]],
threshold = 15)
if(nrow(y)){
datatable(t(y), colnames = rep("", nrow(y)),
options = list(dom = 't'))
}
}
})
output$my_tooltip <- renderUI({
req(tooltipTable())
wellPanel(DTOutput("vals"),
style = 'background-color:#fff; padding:10px; width:400px;border-color:#339fff')
})
output$vals <- renderDT({
tooltipTable()
})
}
shinyApp(ui, server)
在消息队列中推送“我将接受此订购”事件。但是1秒后，Staff A执行了相同的操作。后台工作人员尚未处理队列，因此两名工作人员均收到“确定”响应。鉴于存在冲突，Staff B的请求应已被拒绝。
除了直接的数据库更新之外，是否还有其他方法可以在消息队列的上下文中处理这种情况？