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Diffstat (limited to 'doc/refchan.n')
| -rw-r--r-- | doc/refchan.n | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/doc/refchan.n b/doc/refchan.n index 42e5588..b2bcabb 100644 --- a/doc/refchan.n +++ b/doc/refchan.n @@ -4,7 +4,7 @@ '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" -'\" RCS: @(#) $Id: refchan.n,v 1.11.2.1 2009/08/06 22:28:44 andreas_kupries Exp $ +'\" RCS: @(#) $Id: refchan.n,v 1.11.2.2 2010/03/09 21:13:13 andreas_kupries Exp $ .so man.macros .TH refchan n 8.5 Tcl "Tcl Built-In Commands" .BS @@ -168,9 +168,43 @@ negative value implies that the write failed. Returning a value greater than the number of bytes given to the handler, or zero, is forbidden and will cause the Tcl core to throw an error. .PP -If the subcommand throws an error the command which caused its +To signal that the channel is not able to accept data for writing +right now, it is necessary to throw the error "EAGAIN", i.e. to either +.PP +.CS +return -code error EAGAIN +.CE +or +.CS +error EAGAIN +.CE +.PP +For extensibility any error whose value is a negative integer number +will cause the higher layers to set the C-level variable "\fBerrno\fR" +to the absolute value of this number, signaling a system error. +However, note that the exact mapping between these error numbers and +their meanings is operating system dependent. +.PP +For example, while on Linux both +.PP +.CS +return -code error -11 +.CE +and +.CS +error -11 +.CE +.PP +are equivalent to the examples above, using the more readable string "EAGAIN", +this is not true for BSD, where the equivalent number is -35. +.PP +The symbolic string however is the same across systems, and internally +translated to the correct number. No other error value has such a mapping +to a symbolic string. +.PP +If the subcommand throws any other error the command which caused its invocation (usually \fBputs\fR) will appear to have thrown this error. -Any exception beyond \fIerror\fR (e.g. \fIbreak\fR, etc.) is treated +Any exception beyond \fIerror\fR (e.g.\ \fIbreak\fR, etc.) is treated as and converted to an error. .RE .TP |