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diff --git a/doc/tevent_events.dox b/doc/tevent_events.dox new file mode 100644 index 0000000..94fed9c --- /dev/null +++ b/doc/tevent_events.dox @@ -0,0 +1,341 @@ +/** +@page tevent_events Chapter 2: Tevent events +@section pools Tevent events + +Ok, after reading previous chapter we can start doing something useful. So, the +way of creating events is similar for all types - signals, file descriptors, +time or immediate events. At the beginning it is good to know about some +typedefs which are set in tevent library and which specify the arguments for +each callback. These callbacks are: + +- tevent_timer_handler_t() + +- tevent_immediate_handler_t() + +- tevent_signal_handler_t() + +- tevent_fd_handler_t() + +According their names it is obvious that for creating callback for e.g. time +event, tevent_timer_handler_t will be used. + +The best way how to introduce registering an event and setting up a callback +would be example, so examples describing all the types of events follow. + +@subsection Time Time event + +This example shows how to set up an event which will be repeated for a minute +with interval of 2 seconds (will be triggered 30 times). After exceeding this +limit, the event loop will finish and all the memory resources will be freed. +This is just example describing repeated activity, nothing useful is done +within foo function + +@code +#include <stdio.h> +#include <unistd.h> +#include <tevent.h> +#include <sys/time.h> + +struct state { + struct timeval endtime; + int counter; + TALLOC_CTX *ctx; +}; + +static void callback(struct tevent_context *ev, struct tevent_timer *tim, + struct timeval current_time, void *private_data) +{ + struct state *data = talloc_get_type_abort(private_data, struct state); + struct tevent_timer *time_event; + struct timeval schedule; + + printf("Data value: %d\n", data->counter); + data->counter += 1; // increase counter + + // if time has not reached its limit, set another event + if (tevent_timeval_compare(¤t_time, &(data->endtime)) < 0) { + // do something + // set repeat with delay 2 seconds + schedule = tevent_timeval_current_ofs(2, 0); + time_event = tevent_add_timer(ev, data->ctx, schedule, callback, data); + if (time_event == NULL) { // error ... + fprintf(stderr, "MEMORY PROBLEM\n"); + return; + } + } else { + // time limit exceeded + } +} + +int main(void) { + struct tevent_context *event_ctx; + TALLOC_CTX *mem_ctx; + struct tevent_timer *time_event; + struct timeval schedule; + + mem_ctx = talloc_new(NULL); // parent + event_ctx = tevent_context_init(mem_ctx); + + struct state *data = talloc(mem_ctx, struct state); + + schedule = tevent_timeval_current_ofs(2, 0); // +2 second time value + data->endtime = tevent_timeval_add(&schedule, 60, 0); // one minute time limit + data->ctx = mem_ctx; + data->counter = 0; + + // add time event + time_event = tevent_add_timer(event_ctx, mem_ctx, schedule, callback, data); + if (time_event == NULL) { + fprintf(stderr, "FAILED\n"); + return EXIT_FAILURE; + } + + tevent_loop_wait(event_ctx); + talloc_free(mem_ctx); + return EXIT_SUCCESS; +} +@endcode + +Variable <code>counter</code> is only used for counting the number of triggered +functions. List of all available functions which tevent offers for working with +time are listed +<a href="http://tevent.samba.org/group__tevent__helpers.html">here</a> together +with their description. More detailed view at these functions is unnecessary +because their purpose and usage is quite simple and clear. + +@subsection Immediate Immediate event + +These events are, as their name indicates, activated and performed immediately. +It means that this kind of events have priority over others (except signal +events). So if there is a bulk of events registered and after that a +tevent loop is launched, then all the immediate events will be triggered before +the other events. Except other immediate events (and signal events) because +they are also processed sequentially - according the order they were scheduled. +Signals have the highest priority and therefore they are processed +preferentially. Therefore the expression immediate may not correspond exactly +to the dictionary definition of "something without delay" but rather "as soon +as possible" after all preceding immediate events. + +For creating an immediate event there is a small different which lies in the +fact that the creation of such event is done in 2 steps. One represents the +creation (memory allocation), the second one represents registering as the +event within some tevent context. + +@code +struct tevent_immediate *run(TALLOC_CTX* mem_ctx, + struct tevent_context event_ctx, + void * data) +{ + struct tevent_immediate *im; + + im = tevent_create_immediate(mem_ctx); + if (im == NULL) { + return NULL; + } + tevent_schedule_immediate(im, event_ctx, foo, data); + + return im; +} +@endcode + +Example which may be compiled and run representing the creation of immediate event. + +@code + +#include <stdio.h> +#include <unistd.h> +#include <tevent.h> + +struct info_struct { + int counter; +}; + +static void foo(struct tevent_context *ev, struct tevent_immediate *im, + void *private_data) +{ + struct info_struct *data = talloc_get_type_abort(private_data, struct info_struct); + printf("Data value: %d\n", data->counter); +} + +int main (void) { + struct tevent_context *event_ctx; + TALLOC_CTX *mem_ctx; + struct tevent_immediate *im; + + printf("INIT\n"); + + mem_ctx = talloc_new(NULL); + event_ctx = tevent_context_init(mem_ctx); + + struct info_struct *data = talloc(mem_ctx, struct info_struct); + + // setting up private data + data->counter = 1; + + // first immediate event + im = tevent_create_immediate(mem_ctx); + if (im == NULL) { + fprintf(stderr, "FAILED\n"); + return EXIT_FAILURE; + } + tevent_schedule_immediate(im, event_ctx, foo, data); + + tevent_loop_wait(event_ctx); + talloc_free(mem_ctx); + + return 0; +} +@endcode + +@subsection Signal Signal event + +This is an alternative to standard C library functions signal() or sigaction(). +The main difference that distinguishes these ways of treating signals is their +setting up of handlers for different time intervals of the running program. + +While standard C library methods for dealing with signals offer sufficient +tools for most cases, they are inadequate for handling signals within the +tevent loop. It could be necessary to finish certain tevent requests within the +tevent loop without interruption. If a signal was sent to a program at a moment +when the tevent loop is in progress, a standard signal handler would not return +processing to the application at the very same place and it would quit the +tevent loop for ever. In such cases, tevent signal handlers offer the +possibility of dealing with these signals by masking them from the rest of +application and not quitting the loop, so the other events can still be +processed. + +Tevent offers also a control function, which enables us to verify whether it is +possible to handle signals via tevent, is defined within tevent library and it +returns a boolean value revealing the result of the verification. + +@code +bool tevent_signal_support (struct tevent_context *ev) +@endcode + +Checking for signal support is not necessary, but if it is not guaranteed, this +is a good and easy control to prevent unexpected behaviour or failure of the +program occurring. Such a test of course does not have to be run every single +time you wish to create a signal handler, but simply at the beginning - during +the initialization procedures of the program. Afterthat, simply adapt to each +situation that arises. + +@code + +#include <stdio.h> +#include <tevent.h> +#include <signal.h> + +static void handler(struct tevent_context *ev, + struct tevent_signal *se, + int signum, + int count, + void *siginfo, + void *private_data) +{ + + // Do something useful + + printf("handling signal...\n"); + exit(EXIT_SUCCESS); +} + +int main (void) +{ + struct tevent_context *event_ctx; + TALLOC_CTX *mem_ctx; + struct tevent_signal *sig; + + mem_ctx = talloc_new(NULL); //parent + if (mem_ctx == NULL) { + fprintf(stderr, "FAILED\n"); + return EXIT_FAILURE; + } + + event_ctx = tevent_context_init(mem_ctx); + if (event_ctx == NULL) { + fprintf(stderr, "FAILED\n"); + return EXIT_FAILURE; + } + + if (tevent_signal_support(event_ctx)) { + // create signal event + sig = tevent_add_signal(event_ctx, mem_ctx, SIGINT, 0, handler, NULL); + if (sig == NULL) { + fprintf(stderr, "FAILED\n"); + return EXIT_FAILURE; + } + tevent_loop_wait(event_ctx); + } + + talloc_free(mem_ctx); + return EXIT_SUCCESS; +} +@endcode + + +@subsection File File descriptor event + +Support of events on file descriptors is mainly useful for socket communication +but it certainly works flawlessly with standard streams (stdin, stdout, stderr) + as well. Working asynchronously with file descriptors enables switching + within processing I/O operations. This ability may rise with a greater + number of I/O operations and such overlapping leads to enhancement of the + throughput. + +There are several other functions included in tevent API related to handling +file descriptors (there are too many functions defined within tevent therefore +just some of them are fully described within this thesis. The +declaration of the rest can be easily found on the library’s website or +directly from the source code): + +<ul> +<li>tevent_fd_set_close_fn() - can add another function to be called at the + moment when a structure tevent fd is freed.</li> +<li>tevent_fd_set_auto_close() - calling this function can simplify the + maintenance of file descriptors, because it instructs tevent to close the + appropriate file descriptor when the tevent fd structure is about to be + freed.</li> +<li>tevent_fd_get_flags() - returns flags which are set on the file descriptor + connected with this tevent fd structure.</li> +<li>tevent_fd_set_flags() - sets specified flags on the event’s file + descriptor.</li> +</ul> + +@code + +static void close_fd(struct tevent_context *ev, struct tevent_fd *fd_event, + int fd, void *private_data) +{ + // processing when fd_event is freed +} + +struct static void handler(struct tevent_context *ev, + struct tevent_fd *fde, + uint16_t flags, + void *private_data) +{ + // handling event; reading from a file descriptor + tevent_fd_set_close_fn (fd_event, close_fd); +} + +int run(TALLOC_CTX *mem_ctx, struct tevent_context *event_ctx, + int fd, uint16_t flags, char *buffer) +{ + struct tevent_fd* fd_event = NULL; + + if (flags & TEVENT_FD_READ) { + fd_event = tevent_add_fd(event_ctx, + mem_ctx, + fd, + flags, + handler, + buffer); + } + if (fd_event == NULL) { + // error handling + } + return tevent_loop_once(); +} +@endcode + +*/ |