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makecontext(2) System Calls Manual makecontext(2) NAME makecontext, swapcontext - Provides 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 stan- dards as follows: makecontext(), swapcontext(): XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry 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, execu- tion stack, and machine registers. (See ucontext(5) for more informa- tion about the format of the ucontext structure.) Specifies a function to be called when program execution begins in the new context. Speci- fies the number of parameters passed to the func() function. You in- clude the parameters themselves following the argc parameter. Pointer to the ucontext structure that holds the current context structure. 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 re- sumed when the context modified by makecontext() returns. You initial- ize 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 de- scribed 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 in- dicate the error. ERRORS The makecontext() or swapcontext() functions set errno to the specified values for the following conditions: The ucp parameter has too little stack left to complete the operation. RELATED INFORMATION Functions: exit(2), getcontext(2), sigaction(2), sigprocmask(2) Files: ucontext(5) Standards: standards(5) delim off makecontext(2)