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Andreas Jaeger 2001-05-05 14:43:14 +00:00
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@ -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.
- 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.
- 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).
- 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.
- 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