R / igraph：任何在深度优先搜索回调中获取/设置顶点属性的调用都会导致段错误 [英] R / igraph : any call to get/set vertex attribute within a depth-first-search callback causes a segfault

问题描述

我发现在回调中使用igraph库获取/设置顶点属性的任何调用都会导致R中出现段错误。例如，来自一段代码的平凡回调：

  dfsCallBack < -  function（graph，data，extra）{
 cat（in：，paste（collapse =，，data） \ n）
 distFromRoot < -  data [2] 
 vertexID < -  data [1] 
 set.vertex.attribute（graph，0，name ='color'，value ='blue'）
 FALSE 
} 
 graph.dfs（g，1，in.callback = dfsCallBack）
  

生成此错误：

  graph.dfs（g，1，in。 callback = dfsCallBack）
 in：0，0 
 
 ***发现段错误*** 
地址0x0，导致'内存未映射'
 
 Traceback：
 1：.Call（R_igraph_dfs，graph，root，neimode，unreachable，as.logical（order），as.logical（order.out），as.logical（father），as.logical dist），in.callback，out.callback，extra，rho，PACKAGE =igr aph）
 2：graph.dfs（g，1，in.callback = dfsCallBack）
 
可能的操作：
 1：abort（如果启用了核心转储）
 2：正常R退出
 3：退出R而不保存工作区
 4：退出R保存工作区
选择：
  

这里有什么问题？另外，igraph在处理这些错误时应该更加健壮，崩溃掉R对于像R这样的高级语言来说并不理想。

解决方案如果你说 set.vertex.attribute（

图表，...），图表实际上没有改变，但是新的副本返回并更新了属性。 R对象（几乎总是）不可变的，你不能改变它们，只能根据它们创建新的对象。 属性（图形0，name ='color'，value ='blue'）是错误的，因为顶点id从1开始，所以0无效。这应该被报告为一个错误，并且已经在我们的开发树中修复了。 这不是错误，而是错误。 igraph错误不会崩溃R，他们只是给出错误消息。由于igraph代码和R在同一个线程中运行，因此igraph错误可能会导致R崩溃，除了避免错误之外，我们无法做到这一点。

我建议使用 igraph.dfs 的结果适当地设置属性。您当然可以使用回调来记录信息，或者终止DFS。

I'm finding that any call to get/set vertex attribute using the igraph library within callback causes a segfault in R. For example, the trivial callback from a segment of code:

  dfsCallBack <- function(graph, data, extra) {
    cat("in:", paste(collapse=", ", data), "\n")
    distFromRoot <- data[2]
    vertexID <- data[1]
    set.vertex.attribute(graph, 0, name = 'color', value = 'blue')
    FALSE    
  }
  graph.dfs(g, 1, in.callback = dfsCallBack)

Produces this error:

  graph.dfs(g, 1, in.callback = dfsCallBack)
in: 0, 0 

 *** caught segfault ***
address 0x0, cause 'memory not mapped'

Traceback:
 1: .Call("R_igraph_dfs", graph, root, neimode, unreachable, as.logical(order),     as.logical(order.out), as.logical(father), as.logical(dist),     in.callback, out.callback, extra, rho, PACKAGE = "igraph")
 2: graph.dfs(g, 1, in.callback = dfsCallBack)

Possible actions:
1: abort (with core dump, if enabled)
2: normal R exit
3: exit R without saving workspace
4: exit R saving workspace
Selection: 

What's wrong here? Also, igraph should probably be more robust in dealing with these errors, crashing out of R is not ideal for a high-level language like R.

解决方案

A couple of points.

1. If you say set.vertex.attribute(graph, ...), graph is actually not changed, but a new copy is returned with the attribute updated. R objects are (almost always) immutable, you cannot change them, only create new objects based on them.

2. set.vertex.attribute(graph, 0, name = 'color', value = 'blue') is wrong, because vertex ids start at 1, so the 0 is invalid. This should be reported as an error, and was already fixed in our development tree.

3. This is not an error, it is a bug. igraph errors do not crash R, they just give an error message. Because the igraph code and R run in the same thread, igraph bugs might crash R, and apart from avoiding bugs, there is not much we can do about this.

I would suggest to use the results of igraph.dfs to set the attributes appropriately. You can of course use the callback to record information, or to terminate the DFS.

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