SYNOPSIS<\/a>
DESCRIPTION<\/a>
RETURN VALUE<\/a>
ERRORS<\/a>
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NOTES<\/a>
SEE ALSO<\/a>
COLOPHON<\/a> <\/p>\n
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NAME <\/a> <\/h2>\ngetcontext, setcontext \u2212 get or set the user context<\/p>\n
SYNOPSIS <\/a> <\/h2>\n#include <\/b><\/p>\nint getcontext(ucontext_t *<\/b>ucp<\/i>);
int setcontext(const ucontext_t *<\/b>ucp<\/i>);<\/b><\/p>\nDESCRIPTION <\/a> <\/h2>\nIn a System V-like environment, one has the two types mcontext_t<\/i> and ucontext_t<\/i> defined in <\/i> and the four functions getcontext<\/b>(), setcontext<\/b>(), makecontext<\/b>(3), and swapcontext<\/b>(3) that allow user-level context switching between multiple threads of control within a process.<\/p>\nThe mcontext_t<\/i> type is machine-dependent and opaque. The ucontext_t<\/i> type is a structure that has at least the following fields:<\/p>\n
typedef struct ucontext_t {
struct ucontext_t *uc_link;
sigset_t uc_sigmask;
stack_t uc_stack;
mcontext_t uc_mcontext;
…
} ucontext_t;<\/p>\n
with sigset_t<\/i> and stack_t<\/i> defined in <\/i>. Here uc_link<\/i> points to the context that will be resumed when the current context terminates (in case the current context was created using makecontext<\/b>(3)), uc_sigmask<\/i> is the set of signals blocked in this context (see sigprocmask<\/b>(2)), uc_stack<\/i> is the stack used by this context (see sigaltstack<\/b>(2)), and uc_mcontext<\/i> is the machine-specific representation of the saved context, that includes the calling thread\u2019s machine registers.<\/p>\nThe function getcontext<\/b>() initializes the structure pointed to by ucp<\/i> to the currently active context.<\/p>\n
The function setcontext<\/b>() restores the user context pointed to by ucp<\/i>. A successful call does not return. The context should have been obtained by a call of getcontext<\/b>(), or makecontext<\/b>(3), or received as the third argument to a signal handler (see the discussion of the SA_SIGINFO<\/b> flag in sigaction<\/b>(2)).<\/p>\n
If the context was obtained by a call of getcontext<\/b>(), program execution continues as if this call just returned.<\/p>\n
If the context was obtained by a call of makecontext<\/b>(3), program execution continues by a call to the function func<\/i> specified as the second argument of that call to makecontext<\/b>(3). When the function func<\/i> returns, we continue with the uc_link<\/i> member of the structure ucp<\/i> specified as the first argument of that call to makecontext<\/b>(3). When this member is NULL, the thread exits.<\/p>\n
If the context was obtained by a call to a signal handler, then old standard text says that “program execution continues with the program instruction following the instruction interrupted by the signal”. However, this sentence was removed in SUSv2, and the present verdict is “the result is unspecified”.<\/p>\n
RETURN VALUE <\/a> <\/h2>\nWhen successful, getcontext<\/b>() returns 0 and setcontext<\/b>() does not return. On error, both return \u22121 and set errno<\/i> appropriately.<\/p>\nERRORS <\/a> <\/h2>\nNone defined.<\/p>\n
ATTRIBUTES <\/a> <\/h2>\nFor an explanation of the terms used in this section, see attributes<\/b>(7).<\/p>\n
#include int getcontext(ucontext_t *<\/b>ucp<\/i>); In a System V-like environment, one has the two types mcontext_t<\/i> and ucontext_t<\/i> defined in The mcontext_t<\/i> type is machine-dependent and opaque. The ucontext_t<\/i> type is a structure that has at least the following fields:<\/p>\n typedef struct ucontext_t { with sigset_t<\/i> and stack_t<\/i> defined in The function getcontext<\/b>() initializes the structure pointed to by ucp<\/i> to the currently active context.<\/p>\n The function setcontext<\/b>() restores the user context pointed to by ucp<\/i>. A successful call does not return. The context should have been obtained by a call of getcontext<\/b>(), or makecontext<\/b>(3), or received as the third argument to a signal handler (see the discussion of the SA_SIGINFO<\/b> flag in sigaction<\/b>(2)).<\/p>\n If the context was obtained by a call of getcontext<\/b>(), program execution continues as if this call just returned.<\/p>\n If the context was obtained by a call of makecontext<\/b>(3), program execution continues by a call to the function func<\/i> specified as the second argument of that call to makecontext<\/b>(3). When the function func<\/i> returns, we continue with the uc_link<\/i> member of the structure ucp<\/i> specified as the first argument of that call to makecontext<\/b>(3). When this member is NULL, the thread exits.<\/p>\n If the context was obtained by a call to a signal handler, then old standard text says that “program execution continues with the program instruction following the instruction interrupted by the signal”. However, this sentence was removed in SUSv2, and the present verdict is “the result is unspecified”.<\/p>\n When successful, getcontext<\/b>() returns 0 and setcontext<\/b>() does not return. On error, both return \u22121 and set errno<\/i> appropriately.<\/p>\n None defined.<\/p>\n For an explanation of the terms used in this section, see attributes<\/b>(7).<\/p>\n
int setcontext(const ucontext_t *<\/b>ucp<\/i>);<\/b><\/p>\nDESCRIPTION <\/a> <\/h2>\n
struct ucontext_t *uc_link;
sigset_t uc_sigmask;
stack_t uc_stack;
mcontext_t uc_mcontext;
…
} ucontext_t;<\/p>\nRETURN VALUE <\/a> <\/h2>\n
ERRORS <\/a> <\/h2>\n
ATTRIBUTES <\/a> <\/h2>\n
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