diff options
Diffstat (limited to 'FAQ.in')
| -rw-r--r-- | FAQ.in | 46 |
1 files changed, 23 insertions, 23 deletions
@@ -1602,29 +1602,29 @@ this should be necessary. supports synchronous context switches only. There are several reasons for this: - o UNIX provides no other (portable) way of effecting a synchronous - context switch (also known as co-routine switch). Some versions - support this via setjmp()/longjmp() but this does not work - universally. - - o As defined by the UNIX '98 standard, the only way setcontext() - could trigger an asychronous context switch is if this function - were invoked on the ucontext_t pointer passed as the third argument - to a signal handler. But according to draft 5, XPG6, XBD 2.4.3, - setcontext() is not among the set of routines that may be called - from a signal handler. - - o If setcontext() were to be used for asynchronous context switches, - all kinds of synchronization and re-entrancy issues could arise and - these problems have already been solved by real multi-threading - libraries (e.g., POSIX threads or Linux threads). - - o Synchronous context switching can be implemented entirely in - user-level and less state needs to be saved/restored than for an - asynchronous context switch. It is therefore useful to distinguish - between the two types of context switches. Indeed, some - application vendors are known to use setcontext() to implement - co-routines on top of normal (heavier-weight) pre-emptable threads. +- UNIX provides no other (portable) way of effecting a synchronous + context switch (also known as co-routine switch). Some versions + support this via setjmp()/longjmp() but this does not work + universally. + +- As defined by the UNIX '98 standard, the only way setcontext() + could trigger an asychronous context switch is if this function + were invoked on the ucontext_t pointer passed as the third argument + to a signal handler. But according to draft 5, XPG6, XBD 2.4.3, + setcontext() is not among the set of routines that may be called + from a signal handler. + +- If setcontext() were to be used for asynchronous context switches, + all kinds of synchronization and re-entrancy issues could arise and + these problems have already been solved by real multi-threading + libraries (e.g., POSIX threads or Linux threads). + +- Synchronous context switching can be implemented entirely in + user-level and less state needs to be saved/restored than for an + asynchronous context switch. It is therefore useful to distinguish + between the two types of context switches. Indeed, some + application vendors are known to use setcontext() to implement + co-routines on top of normal (heavier-weight) pre-emptable threads. It should be noted that if someone was dead-bent on using setcontext() on the third arg of a signal handler, then IA-64 Linux could support |