From: Scott Worley Date: Wed, 13 Sep 2023 21:14:22 +0000 (-0700) Subject: Hold a lock while appending X-Git-Tag: v1.0.0~8 X-Git-Url: http://git.scottworley.com/tl-append/commitdiff_plain/b56e29cbdf58c1baa75e3340ff25c493329f2b9e Hold a lock while appending --- diff --git a/tl-append.c b/tl-append.c index 3e60a24..0650721 100644 --- a/tl-append.c +++ b/tl-append.c @@ -1,6 +1,7 @@ #define _POSIX_C_SOURCE 199309L #include +#include #include #include #include @@ -15,6 +16,7 @@ const char PROMPT[] = "\33[H" /* Move cursor 'home' */ "\33[J" /* Clear screen */ "> "; const char ACKNOWLEDGE[] = "[OK]"; +const char WAITING[] = "[Waiting on lock...]\n"; const struct timespec ACKNOWLEDGE_DELAY = {0, 300000000}; typedef struct { @@ -45,9 +47,7 @@ static void read_line(conf_t conf, char *buf) { } } -static void write_line(conf_t conf, const char *line) { - const char *now = encode_time(time(NULL)); - FILE *f = fopen(FILENAME, "a"); +static void write_line(const char *now, FILE *f, const char *line) { if (f == NULL) die_err("Error opening output file"); if (fputs(now, f) == EOF) @@ -56,8 +56,29 @@ static void write_line(conf_t conf, const char *line) { die("Error writing to output file"); if (fputs(line, f) == EOF) die("Error writing to output file"); - if (fclose(f) != 0) - die_err("Error closing output file"); +} + +static void take_lock(FILE *f) { + struct flock lock; + lock.l_type = F_WRLCK; + lock.l_whence = SEEK_SET; + lock.l_start = 0; + lock.l_len = 0; + int fd = fileno(f); + if (fd == -1) + die_err("Couldn't get file descriptor for locking"); + if (fcntl(fd, F_SETLK, &lock) == 0) + return; + if (errno != EACCES && errno != EAGAIN) + die_err("Couldn't take lock"); + if (fputs(WAITING, stderr) == EOF) + die("Error writing waiting message"); + if (fcntl(fd, F_SETLKW, &lock) == 0) + return; + die_err("Couldn't take lock"); +} + +static void write_acknowledgment(conf_t conf) { if (conf.interactive) { if (fputs(ACKNOWLEDGE, stderr) == EOF) die("Error writing acknowledgment"); @@ -66,11 +87,24 @@ static void write_line(conf_t conf, const char *line) { } } +static void lock_and_write_line(conf_t conf, const char *line) { + const char *now = encode_time(time(NULL)); + FILE *f = fopen(FILENAME, "a"); + + take_lock(f); + write_line(now, f, line); + + if (fclose(f) != 0) + die_err("Error closing output file"); + + write_acknowledgment(conf); +} + int main(int argc, char *argv[]) { conf_t conf = parse_command_line(argc, argv); char buf[BUF_SIZE]; for (read_line(conf, buf); buf[0]; read_line(conf, buf)) { - write_line(conf, buf); + lock_and_write_line(conf, buf); } return 0; }