shm-logging: implement i3-dump-log -f (follow)
This changes the SHM log format, it doesn’t use 0-bytes to separate entries anymore. Instead of using lots of printf() calls in i3-dump-log, we now do precisely one big write(). So, to be clear: i3-dump-log and i3 both need to be upgraded. Mismatching versions will lead to garbage output (no crashes of i3, just garbage output). The -f flag uses an inter-process pthread_cond_t in the shared memory header to broadcast the arrival of new messages to all i3-dump-log processes. This internally uses futexes and thus doesn’t even mean a kernel call in most cases. inter-process pthread_cond_ts require NPTL (the Native Posix Thread Library, introduce in Linux 2.6).
This commit is contained in:
Michael Stapelberg
parent
070a18e598
commit
e68a8dd86c
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@ -2,7 +2,7 @@
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* vim:ts=4:sw=4:expandtab
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*
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* i3 - an improved dynamic tiling window manager
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* © 2009-2011 Michael Stapelberg and contributors (see also: LICENSE)
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* © 2009-2012 Michael Stapelberg and contributors (see also: LICENSE)
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*
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* i3-dump-log/main.c: Dumps the i3 SHM log to stdout.
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*
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@ -28,18 +28,47 @@
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#include "shmlog.h"
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#include <i3/ipc.h>
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static uint32_t offset_next_write,
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wrap_count;
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static i3_shmlog_header *header;
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static char *logbuffer,
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*walk;
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static int check_for_wrap(void) {
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if (wrap_count == header->wrap_count)
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return 0;
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/* The log wrapped. Print the remaining content and reset walk to the top
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* of the log. */
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wrap_count = header->wrap_count;
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write(STDOUT_FILENO, walk, ((logbuffer + header->offset_last_wrap) - walk));
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walk = logbuffer + sizeof(i3_shmlog_header);
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return 1;
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}
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static void print_till_end(void) {
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check_for_wrap();
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int n = write(STDOUT_FILENO, walk, ((logbuffer + header->offset_next_write) - walk));
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if (n > 0) {
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walk += n;
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}
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}
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int main(int argc, char *argv[]) {
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int o, option_index = 0;
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bool verbose = false;
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bool verbose = false,
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follow = false;
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static struct option long_options[] = {
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{"version", no_argument, 0, 'v'},
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{"verbose", no_argument, 0, 'V'},
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{"follow", no_argument, 0, 'f'},
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{"help", no_argument, 0, 'h'},
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{0, 0, 0, 0}
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};
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char *options_string = "s:vVh";
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char *options_string = "s:vfVh";
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while ((o = getopt_long(argc, argv, options_string, long_options, &option_index)) != -1) {
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if (o == 'v') {
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@ -47,9 +76,11 @@ int main(int argc, char *argv[]) {
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return 0;
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} else if (o == 'V') {
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verbose = true;
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} else if (o == 'f') {
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follow = true;
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} else if (o == 'h') {
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printf("i3-dump-log " I3_VERSION "\n");
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printf("i3-dump-log [-s <socket>]\n");
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printf("i3-dump-log [-f] [-s <socket>]\n");
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return 0;
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}
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}
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@ -90,45 +121,61 @@ int main(int argc, char *argv[]) {
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struct stat statbuf;
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int logbuffer_shm = shm_open(shmname, O_RDONLY, 0);
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/* NB: While we must never read, we need O_RDWR for the pthread condvar. */
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int logbuffer_shm = shm_open(shmname, O_RDWR, 0);
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if (logbuffer_shm == -1)
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err(EXIT_FAILURE, "Could not shm_open SHM segment for the i3 log (%s)", shmname);
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if (fstat(logbuffer_shm, &statbuf) != 0)
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err(EXIT_FAILURE, "stat(%s)", shmname);
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char *logbuffer = mmap(NULL, statbuf.st_size, PROT_READ, MAP_SHARED, logbuffer_shm, 0);
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/* NB: While we must never read, we need O_RDWR for the pthread condvar. */
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logbuffer = mmap(NULL, statbuf.st_size, PROT_READ | PROT_WRITE, MAP_SHARED, logbuffer_shm, 0);
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if (logbuffer == MAP_FAILED)
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err(EXIT_FAILURE, "Could not mmap SHM segment for the i3 log");
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i3_shmlog_header *header = (i3_shmlog_header*)logbuffer;
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header = (i3_shmlog_header*)logbuffer;
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if (verbose)
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printf("next_write = %d, last_wrap = %d, logbuffer_size = %d, shmname = %s\n",
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header->offset_next_write, header->offset_last_wrap, header->size, shmname);
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int chars;
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char *walk = logbuffer + header->offset_next_write;
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/* Skip the first line, it very likely is mangled. Not a problem, though,
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* the log is chatty enough to have plenty lines left. */
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while (*walk != '\0')
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walk++;
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walk = logbuffer + header->offset_next_write;
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/* Print the oldest log lines. We use printf("%s") to stop on \0. */
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while (walk < (logbuffer + header->offset_last_wrap)) {
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chars = printf("%s", walk);
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/* Shortcut: If there are two consecutive \0 bytes, this part of the
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* buffer was never touched. To not call printf() for every byte of the
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* buffer, we directly exit the loop. */
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if (*walk == '\0' && *(walk+1) == '\0')
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break;
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walk += (chars > 0 ? chars : 1);
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/* We first need to print old content in case there was at least one
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* wrapping already. */
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if (*walk != '\0') {
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/* In case there was a write to the buffer already, skip the first
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* old line, it very likely is mangled. Not a problem, though, the log
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* is chatty enough to have plenty lines left. */
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while (*walk != '\n')
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walk++;
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walk++;
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}
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/* In case there was no wrapping, this is a no-op, otherwise it prints the
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* old lines. */
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wrap_count = 0;
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check_for_wrap();
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/* Then start from the beginning and print the newer lines */
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walk = logbuffer + sizeof(i3_shmlog_header);
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while (walk < (logbuffer + header->offset_next_write)) {
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chars = printf("%s", walk);
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walk += (chars > 0 ? chars : 1);
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print_till_end();
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if (follow) {
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/* Since pthread_cond_wait() expects a mutex, we need to provide one.
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* To not lock i3 (that’s bad, mhkay?) we just define one outside of
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* the shared memory. */
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pthread_mutex_t dummy_mutex = PTHREAD_MUTEX_INITIALIZER;
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pthread_mutex_lock(&dummy_mutex);
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while (1) {
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pthread_cond_wait(&(header->condvar), &dummy_mutex);
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/* If this was not a spurious wakeup, print the new lines. */
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if (header->offset_next_write != offset_next_write) {
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offset_next_write = header->offset_next_write;
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print_till_end();
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}
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}
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}
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return 0;
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@ -12,11 +12,33 @@
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#define _I3_SHMLOG_H
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#include <stdint.h>
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#include <pthread.h>
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/*
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* Header of the shmlog file. Used by i3/src/log.c and i3/i3-dump-log/main.c.
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*
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*/
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typedef struct i3_shmlog_header {
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/* Byte offset where the next line will be written to. */
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uint32_t offset_next_write;
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/* Byte offset where the last wrap occured. */
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uint32_t offset_last_wrap;
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/* The size of the logfile in bytes. Since the size is limited to 25 MiB
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* an uint32_t is sufficient. */
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uint32_t size;
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/* wrap counter. We need it to reliably signal to clients that we just
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* wrapped (clients cannot use offset_last_wrap because that might
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* coincidentally be exactly the same as previously). Overflows can happen
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* and don’t matter — clients use an equality check (==). */
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uint32_t wrap_count;
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/* pthread condvar which will be broadcasted whenever there is a new
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* message in the log. i3-dump-log uses this to implement -f (follow, like
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* tail -f) in an efficient way. */
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pthread_cond_t condvar;
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} i3_shmlog_header;
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#endif
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@ -7,7 +7,7 @@ i3_SOURCES := $(filter-out $(i3_SOURCES_GENERATED),$(wildcard src/*.c)
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i3_HEADERS_CMDPARSER := $(wildcard include/GENERATED_*.h)
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i3_HEADERS := $(filter-out $(i3_HEADERS_CMDPARSER),$(wildcard include/*.h))
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i3_CFLAGS = $(XCB_CFLAGS) $(XCB_KBD_CFLAGS) $(XCB_WM_CFLAGS) $(X11_CFLAGS) $(XCURSOR_CFLAGS) $(YAJL_CFLAGS) $(LIBEV_CFLAGS) $(PCRE_CFLAGS) $(LIBSN_CFLAGS)
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i3_LIBS = $(XCB_LIBS) $(XCB_KBD_LIBS) $(XCB_WM_LIBS) $(X11_LIBS) $(XCURSOR_LIBS) $(YAJL_LIBS) $(LIBEV_LIBS) $(PCRE_LIBS) $(LIBSN_LIBS) -lm
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i3_LIBS = $(XCB_LIBS) $(XCB_KBD_LIBS) $(XCB_WM_LIBS) $(X11_LIBS) $(XCURSOR_LIBS) $(YAJL_LIBS) $(LIBEV_LIBS) $(PCRE_LIBS) $(LIBSN_LIBS) -lm -lpthread
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# When using clang, we use pre-compiled headers to speed up the build. With
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# gcc, this actually makes the build slower.
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36
src/log.c
36
src/log.c
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@ -20,6 +20,7 @@
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#include <sys/mman.h>
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#include <sys/stat.h>
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#include <errno.h>
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#include <pthread.h>
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#if defined(__APPLE__)
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#include <sys/types.h>
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#include <sys/sysctl.h>
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@ -48,6 +49,8 @@ int shmlog_size = 0;
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static char *logbuffer;
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/* A pointer (within logbuffer) where data will be written to next. */
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static char *logwalk;
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/* A pointer to the shmlog header */
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static i3_shmlog_header *header;
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/* A pointer to the byte where we last wrapped. Necessary to not print the
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* left-overs at the end of the ringbuffer. */
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static char *loglastwrap;
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@ -63,8 +66,6 @@ static int logbuffer_shm;
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*
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*/
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static void store_log_markers(void) {
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i3_shmlog_header *header = (i3_shmlog_header*)logbuffer;
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header->offset_next_write = (logwalk - logbuffer);
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header->offset_last_wrap = (loglastwrap - logbuffer);
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header->size = logbuffer_size;
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@ -128,6 +129,18 @@ void init_logging(void) {
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logbuffer = NULL;
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return;
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}
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/* Initialize with 0-bytes, just to be sure… */
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memset(logbuffer, '\0', logbuffer_size);
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header = (i3_shmlog_header*)logbuffer;
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pthread_condattr_t cond_attr;
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pthread_condattr_init(&cond_attr);
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if (pthread_condattr_setpshared(&cond_attr, PTHREAD_PROCESS_SHARED) != 0)
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ELOG("pthread_condattr_setpshared() failed, i3-dump-log -f will not work!\n");
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pthread_cond_init(&(header->condvar), &cond_attr);
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logwalk = logbuffer + sizeof(i3_shmlog_header);
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loglastwrap = logbuffer + logbuffer_size;
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store_log_markers();
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@ -199,22 +212,25 @@ static void vlog(const bool print, const char *fmt, va_list args) {
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fprintf(stderr, "BUG: single log message > 4k\n");
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}
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/* If there is no space for the current message (plus trailing
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* nullbyte) in the ringbuffer, we need to wrap and write to the
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* beginning again. */
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if ((len+1) >= (logbuffer_size - (logwalk - logbuffer))) {
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/* If there is no space for the current message in the ringbuffer, we
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* need to wrap and write to the beginning again. */
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if (len >= (logbuffer_size - (logwalk - logbuffer))) {
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loglastwrap = logwalk;
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logwalk = logbuffer + sizeof(i3_shmlog_header);
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store_log_markers();
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header->wrap_count++;
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}
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/* Copy the buffer, terminate it, move the write pointer to the byte after
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* our current message. */
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/* Copy the buffer, move the write pointer to the byte after our
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* current message. */
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strncpy(logwalk, message, len);
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logwalk[len] = '\0';
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logwalk += len + 1;
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logwalk += len;
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store_log_markers();
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/* Wake up all (i3-dump-log) processes waiting for condvar. */
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pthread_cond_broadcast(&(header->condvar));
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if (print)
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fwrite(message, len, 1, stdout);
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}
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