UCONTEXT_ALLOC(3C) Standard C Library Functions UCONTEXT_ALLOC(3C)

ucontext_alloc, ucontext_free — allocate and free ucontext structures

Standard C Library (libc, -lc)

#include <ucontext.h>

ucontext_t *
ucontext_alloc(uint32_t flags);

void
ucontext_free(ucontext_t *ucp);

The () function allocates and initializes a ucontext_t structure for subsequent use with functions such as getcontext_extd(2) or swapcontext_extd(2).

Traditionally applications declare the ucontext_t structure on the stack, as part of another structure, or in other global data. Due to the advent of extended states (such as the x86 xsave state) the traditional structure is not sufficient to capture all state. The () function determines the correct size for the current process to cover all of its extended states in addition to the standard ucontext_t and then proceeds to set up the other members of the ucontext_t to point at the additional memory.

It is not recommended that the returned ucontext structure be used with either getcontext(2) or swapcontext(2). While the resulting calls will work, they will not preserve that space for the extended state has been allocated. No memory will be leaked as a result of that.

The () function is used to release all the memory associated with ucp. ucp must have come from a prior call to ucontext_alloc(). If it is not, then it is undefined as to what will happen to the program, but it will result in eventual memory corruption. If ucp was declared on the stack, as a structure member, as global data, or allocated in some way that wasn't calling ucontext_alloc(), do not pass it to ucontext_free().

Upon successful completion, the ucontext_alloc() function returns a pointer to an allocated ucontext_t. Otherwise NULL is returned and errno is set to indicate the error.

The ucontext_alloc() function will set errno based on the failure of the underlying memory allocator. For more information and details on these errors, see malloc(3C), the list of errors below may not be exhaustive.

The ucontext_alloc() function will fail if:

The flags argument had unknown or unsupported values.
There was insufficient memory to allocate an extended ucontext structure. See malloc(3C) for more information.
There was insufficient memory to allocate an extended ucontext structure, but the application could try again later. See malloc(3C) for more information.

January 24, 2023 OmniOS