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setjmp.h is a header defined in the C standard library to provide "non-local jumps": control flow that deviates from the usual subroutine call and return sequence. The complementary functions setjmp and longjmp provide this functionality.
For example, if the subroutine modifies a 64-bit global variable on a 32-bit machine, the operation may be split into two 32-bit operations, and thus, if the subroutine is interrupted while executing, and called again from the interrupt handler, the global variable may be in a state where only 32 bits have been updated.
"Instrumenting" all the source code with additional source statements that issue a function that invokes an internal or external debug subroutine, is yet another common approach. This method increases the binary size and might adversely affect normal memory allocation and exception handlers .
In the C Standard Library, signal processing defines how a program handles various signals while it executes. A signal can report some exceptional behavior within the program (such as division by zero), or a signal can report some asynchronous event outside the program (such as someone striking an interactive attention key on a keyboard).
For example, INT 13H will generate the 20th software interrupt (0x13 is nineteen (19) in hexadecimal notation, and the count starts at 0), causing the function pointed to by the 20th vector in the interrupt table to be executed. INT is widely used in real mode. In protected mode, INT is a privileged instruction. [1]
The calling code does nothing but list the subroutines to be called. This puts all the function setup and clean-up code in one place—the prologue and epilogue of the function—rather than in the many places that function is called. This makes threaded code the most compact calling convention. Threaded code passes all arguments on the stack.
This can happen in multi-threaded environments, or even in single-threaded environments when other code (typically called in the destruction of some object) resets the global variable before the checking code. The following example shows a way to avoid this problem (see [dead link ] or ; cf. ). But at the cost of not being able to use return ...
For example, hardware timers send interrupts to the CPU at regular intervals. Most operating systems execute a HLT instruction when there is no immediate work to be done, putting the processor into an idle state. In Windows NT, for example, this instruction is run in the "System Idle Process". On x86 processors, the opcode of HLT is 0xF4.