Question

使用 withCallingHandlers （）无法捕获S4泛型函数的评估参数时，会生成

警告。

withCallingHandlers的正常行为说明：

### simple function that sends a warning
send_warning <- function() {
  warning('send_warning')
}
send_warning()
# Warning message:
# In send_warning() : send_warning

### the warning can be caught by withCallingHandlers
withCallingHandlers(send_warning(), warning = function(w) 
  { stop('got warning:', w) })
# Error in (function (w)  : 
#   got warning:simpleWarning in send_warning(): send_warning

现在，让我们在S4发送期间发出警告：

### simplest method ever
setGeneric('my_method', function(x) standardGeneric('my_method') )
setMethod('my_method', 'ANY', function(x) str(x) )

### call it with an argument that produces a warning: seems to work
my_method(warning('argh'))
#  chr "argh"
# Warning message:
# argh 

### !!! BUT it is not caught !!!!!!!!!!!!!!!!!!:
withCallingHandlers(my_method(warning('argh')), warning = function(w) 
  { stop('got warning:', w) })
#  chr "argh"
# Warning message:
# argh

最后一个示例表明在S4方法调用期间不会发生这种情况：

setGeneric('my_method2', function(x) standardGeneric('my_method2') )
setMethod('my_method2', 'ANY', function(x) warning('my_method2') )
my_method2()
# Warning message:
# In my_method2() : my_method2

### warning is caught
withCallingHandlers(my_method2(), warning = function(w) 
  { stop('got warning:', w) })
# Error in (function (w)  : 
#   got warning:simpleWarning in my_method2(): my_method2

据我所知，S4调度期间发出的警告似乎有特殊行为。我想知道为什么以及如何抓住它们。

Answer 1

我最初的猜测是，这是因为方法调度会发出警告

f = function(x) withCallingHandlers(x, warning=function(w) { 
    cat('muffled\n')
    invokeRestart("muffleWarning")
})

然后

> withCallingHandlers(f(warning("f")), warning=function(w) message("caught"))
muffled

深入挖掘，实际警告调用在此C堆栈跟踪中

#0  do_warning (call=0x3d4ad50, op=0x9c4bf0, args=0x45b9968, rho=0x45b9c40) at /home/mtmorgan/src/R-devel/src/main/errors.c:1140
#1  0x00000000004b4198 in bcEval (body=<optimized out>, rho=<optimized out>, useCache=<optimized out>) at /home/mtmorgan/src/R-devel/src/main/eval.c:4700
#2  0x00000000004bff40 in Rf_eval (e=0x3d45618, rho=0x45b9c40) at /home/mtmorgan/src/R-devel/src/main/eval.c:554
#3  0x00000000004c4e4d in Rf_applyClosure (call=0x45b8630, op=0x3d45730, arglist=<optimized out>, rho=0x9e7638, suppliedenv=0x9e7670) at /home/mtmorgan/src/R-devel/src/main/eval.c:1033
#4  0x00000000004c0005 in Rf_eval (e=0x45b8630, rho=0x9e7638) at /home/mtmorgan/src/R-devel/src/main/eval.c:670
#5  0x00000000004c0695 in forcePromise (e=0x45b9410) at /home/mtmorgan/src/R-devel/src/main/eval.c:458
#6  0x00000000004c0462 in Rf_eval (e=0xa1d338, rho=0x45b9368) at /home/mtmorgan/src/R-devel/src/main/eval.c:577
#7  0x000000000046fbfb in protectedEval (d=0x7fffffffc7f0) at /home/mtmorgan/src/R-devel/src/main/context.c:750
#8  0x0000000000470d48 in R_ToplevelExec (fun=0x46fbe0 <protectedEval>, data=0x7fffffffc7f0) at /home/mtmorgan/src/R-devel/src/main/context.c:705
#9  0x0000000000470de7 in R_tryEval (e=<optimized out>, env=<optimized out>, ErrorOccurred=0x7fffffffc89c) at /home/mtmorgan/src/R-devel/src/main/context.c:764
#10 0x0000000000470e26 in R_tryEvalSilent (e=<optimized out>, env=<optimized out>, ErrorOccurred=<optimized out>) at /home/mtmorgan/src/R-devel/src/main/context.c:787
#11 0x00007ffff49230b9 in R_dispatchGeneric (fname=0x44b37e8, ev=0x45b9368, fdef=0x45b92f8) at /home/mtmorgan/src/R-devel/src/library/methods/src/methods_list_dispatch.c:993
#12 0x00000000004f5337 in do_standardGeneric (call=<optimized out>, op=<optimized out>, args=<optimized out>, env=0x45b9368) at /home/mtmorgan/src/R-devel/src/main/objects.c:1167
....

在R_dispatchGeneric方法的C代码中，dispatch试图通过评估它来弄清楚参数的类

989         if(arg_sym == R_dots) {
990         thisClass = dots_class(ev, &check_err);
991         }
992         else {
993         PROTECT(arg = R_tryEvalSilent(arg_sym, ev, &check_err));
994         if(!check_err)
995             thisClass = R_data_class(arg, TRUE);
996         UNPROTECT(1); /* for arg */
997         }

这似乎是为了实现C级错误处理程序：

998         if(check_err)
999         error(_("error in evaluating the argument '%s' in selecting a method for function '%s': %s"),
1000                  CHAR(PRINTNAME(arg_sym)),CHAR(asChar(fname)),
1001                  R_curErrorBuf());

Rf_tryEvalSilent在顶级评估，类似于命令提示符，其中没有建立调用处理程序;您可以在C代码中看到这一点，其中处理程序堆栈设置为NULL

686 Rboolean R_ToplevelExec(void (*fun)(void *), void *data)
687 {
688     RCNTXT thiscontext;
689     RCNTXT * volatile saveToplevelContext;
690     volatile SEXP topExp, oldHStack;
691     Rboolean result;
692 
693 
694     PROTECT(topExp = R_CurrentExpr);
695     PROTECT(oldHStack = R_HandlerStack);
696     R_HandlerStack = R_NilValue;
697     saveToplevelContext = R_ToplevelContext;

由于参数评估在没有处理程序的情况下开始，因此可以使用

my_method(withCallingHandlers(warning('arrgh'), warning=function(w) ...))

但这可能不实用。

如何捕获S4方法选择期间发送的警告

1 个答案: