Advanced Signals with sigqueue and sigaction in Java Encoding PDF417 in Java Advanced Signals with sigqueue and sigaction

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Advanced Signals with sigqueue and sigaction using jvm tobuild pdf417 in web,windows application Visual Studio Development Language Finally, we come spring framework barcode pdf417 to an alternative to the kill system call named sigqueue. The prototype is shown below and looks much like the kill system call except that it takes an additional argument:. int sigqueue(pid_ t pid, int sig, const union sigval value);. Signals The pid and sig a rguments are identical to the kill system call, but the value argument actually lets you include data with the signal. Recall that non real time signals are not queued, so only when you use a signal number between RTSIGMIN and RTSIGMAX will the signals be queued with their associated information. The additional information provided by the sigqueue function can be retrieved only by a handler installed with the sigaction function, which I introduced earlier as an alternative to the signal system call.

Installing a handler with sigaction is a bit more involved. Using Listing 7-6 as an example, the signal function could be replaced by sigaction as follows:. struct sigaction jar PDF 417 sa = { .sa_handler = handler, .sa_flags = SA_RESTART }; sigemptyset(&sa.

sa_mask); sigaction(SIGRTMIN,&sa,NULL);. Using C99 structu re initializer syntax . . .

Same handler as before Rearm the signal handler after it s called . . .

Create an empty signal mask Discard the old action via NULL. Filling in the si Java pdf417 gaction structure is an extra step required to use the sigaction function. The sa_mask field is a signal mask that is used while the signal handler runs. Normally, when the signal handler is called, the signal being handled is blocked.

The mask specified here indicates additional signals to be blocked while the handler runs. The handler in the sigaction structure is a pointer to a function. This is actually a union containing pointers to two different handler types.

sa_handler points to a System V style signal handler, used above. sa_sigaction points to a new-style handler that has the following prototype:. void handler(int sig, struct siginfo *si, void *ptr). To take full adva jsp pdf417 2d barcode ntage of sigqueue, you should define a new-style handler. To indicate that you are using a new-style handler, you set the SA_SIGINFO flag in the sa_flags field as follows:. struct sigaction sa = { .sa_sigaction = handler, .sa_flags = SA_RESTART SA_SIGINFO }; sig jar pdf417 2d barcode emptyset(&sa.sa_mask);. Using C99 structu re initializer . . .

Use new-style handler DON T FORGET THIS!. When the kernel s PDF417 for Java ees the SA_SIGINFO flag, it puts different arguments on the stack for the signal handler. Without this, your signal handler will be called with the wrong arguments and probably will cause your application to crash with a SIGSEGV..

7 Communication between Processes Now that you have jsp PDF-417 2d barcode a new-style handler, you can replace the kill function with sigqueue as follows:. union sigval sv = { .sival_int = 42 }; sigqueue(getppid(), SIGRTMIN, sv);. Any user-defined number will do. You can use any signal, but only RT signals are queued. Looking at the ha ndler again, the siginfo structure contains various things defined by different standards. Following are the set of values used in Linux and their POSIX definitions:. int si_signo int PDF-417 2d barcode for Java si_code int si_errno pid_t si_pid uid_t si_uid void *si_addr int si_status long si_band union sigval si_value. Signal number S IGINT and so on Signal code (see text) If nonzero, an errno value associated with this signal Sending process ID Real user ID of sending process (see text) Exit value or signal Band event for SIGPOLL Signal value. As the annotation j2se barcode pdf417 above suggests, several signal-specific fields in the siginfo structure are not defined under all circumstances. Of all the fields defined, only the si_signo, si_errno, and si_code fields contain valid data all the time, according to POSIX. If the signal is sent by another process, si_pid and si_uid indicate the process ID and user ID of the process that sent the signal.

The si_code takes one of the values defined in Table 7-4 and indicates some details about the source of the signal and the reason for it. A signal that was the result of another process or a call to the raise function results in an si_code value of SI_USER. A signal that is sent with the sigqueue function has an si_code value of SI_QUEUE.

An example of a context-sensitive field is the si_value field, which is defined only if the caller used sigqueue to send the signal. When this is true, si_value contains a copy of the sigval that was sent by the function. Most of the other fields deal with various exception conditions that have nothing to do with IPC and come from the current process.

Another context-sensitive field, si_errno may be nonzero if an error is associated with this signal. si_band is defined only for SIGPOLL, which can be useful in certain IPC applications..

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