makecontext(2) [osf1 man page]
makecontext(2) System Calls Manual makecontext(2) NAME
makecontext, swapcontext - Manipulate user level context switching SYNOPSIS
#include <ucontext.h> void makecontext( ucontext_t *ucp, void (*func)(), int argc ... ); int swapcontext( ucontext_t *oucp, const ucontext_t *ucp ); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: makecontext(), swapcontext(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Provides a pointer to a ucontext structure, defined in the <ucontext.h> header file. The ucontext structure contains the signal mask, exe- cution stack, and machine registers. (See ucontext(5) for more information about the format of the ucontext structure.) Specifies a func- tion to be called when program execution begins in the new context. Specifies the number of parameters passed to the func() function. You include the parameters themselves following the argc parameter. Pointer to the ucontext structure that holds the current context struc- ture. DESCRIPTION
The makecontext() function modifies the context specified by the ucp parameter. Before you call the makecontext() function, call the get- context() function to initialize the ucp parameter. Before you call the makecontext() function, you should allocate a stack for the new context. Also, you should initialize the uc_link member of the ucontext structure. This member determines the context that is resumed when the context modified by makecontext() returns. You ini- tialize the uc_link member by calling the getcontext() function. To execute the new context, call the setcontext() or swapcontext() function. Program execution begins by calling the function specified in the func parameter. Any parameters you specify following the argc parameter are passed to the func() function. The swapcontext() function switches between two user contexts. The function stores the current context in the oucp parameter. It then switches execution to the context described by the ucp parameter. When the new context finishes execution, control returns to the context described by the oucp parameter. RETURN VALUES
The makecontext() function does not return. On success, the swapcontext() function returns 0 (zero). On failure the swapcontext() function returns a value of -1 and sets errno to indicate the error. ERRORS
The makecontext() or swapcontext() functions set errno to the specified values for the following conditions: The ucp parameter has too lit- tle stack left to complete the operation. SEE ALSO
Functions: exit(2), getcontext(2), sigaction(2), sigprocmask(2) Files: ucontext(5) Standards: standards(5) makecontext(2)
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getcontext(2) System Calls Manual getcontext(2) NAME
getcontext, setcontext - Initiates and restores user level context switching SYNOPSIS
#include <ucontext.h> int getcontext( ucontext_t *ucp ); int setcontext( const ucontext_t *ucp ); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: getcontext(), setcontext(): XSH5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
Provides a pointer to a ucontext structure, defined in the <ucontext.h> header file. The ucontext structure contains the signal mask, exe- cution stack, and machine registers. (See ucontext(5) for more information about the format of the ucontext structure.) DESCRIPTION
Using both the getcontext() and setcontext() functions enables you to initiate user level context control, switching between multiple threads of control within a single process. When you call getcontext(), it initializes the ucp argument to the current user context of the calling process. Use the setcontext() function to restore the state of the user context pointed to by the ucp argument. The setcontext() function, if suc- cessful, does not return; application execution continues from the point specified by the ucontext structure you pass to the setcontext() function. The ucontext structure that you pass to the setcontext() function must have been created by a call to the getcontext() function or the makecontext() function, or have been passed as the third argument to a signal handler. (The third argument in a call to the sigaction() function determines the action to be performed when a signal is delivered. For more information, see sigaction(2).) When a context structure is created by the getcontext() function, execution of the program continues as if the corresponding call of the getcontext() function had just returned. When a context structure is created by the makecontext() function, program execution continues with the function passed to makecontext(). When that function returns, the thread continues as if after a call to setcontext() with the context structure argument that was input to makecontext(). If the uc_link member of the ucontext_t structure pointed to by the ucp argument is 0 (zero), then this context is the main context, and the thread will exit when this context returns. The effects of passing a ucp argument from any other source are unspecified. NOTES
When a signal handler executes, the current user context is saved and a new context is created by the kernel. If the process leaves the signal handler using the longjmp() function, the original context cannot be restored, and the result of future calls to the getcontext() function are unpredictable. Use the siglongjmp() or setcontext() functions in signal handlers, instead of the longjmp() function. RETURN VALUES
The setcontext() function does not return upon success. The getcontext() function returns 0 (zero) upon success. Upon failure, both the setcontext() and getcontext() functions return a value of -1. SEE ALSO
Functions: bsd_signal(2), makecontext(2), sigaction(2), sigaltstack(2), sigprocmask(2), setjmp(3), sigsetjmp(3) Files: ucontext(5) Standards: standards(5) getcontext(2)