diff options
Diffstat (limited to 'utils/xshm.c')
| -rw-r--r-- | utils/xshm.c | 340 |
1 files changed, 340 insertions, 0 deletions
diff --git a/utils/xshm.c b/utils/xshm.c new file mode 100644 index 0000000..8992140 --- /dev/null +++ b/utils/xshm.c @@ -0,0 +1,340 @@ +/* xscreensaver, Copyright (c) 1993-2017 Jamie Zawinski <jwz@jwz.org> + * + * Permission to use, copy, modify, distribute, and sell this software and its + * documentation for any purpose is hereby granted without fee, provided that + * the above copyright notice appear in all copies and that both that + * copyright notice and this permission notice appear in supporting + * documentation. No representations are made about the suitability of this + * software for any purpose. It is provided "as is" without express or + * implied warranty. + */ + +/* The MIT-SHM (Shared Memory) extension is pretty tricky to use. + This file contains the common boiler-plate for creating a shared + XImage structure, and for making sure that the shared memory segments + get allocated and shut down cleanly. + + This code currently deals only with shared XImages, not with shared Pixmaps. + It also doesn't use "completion events", but so far that doesn't seem to + be a problem (and I'm not entirely clear on when they would actually be + needed, anyway.) + + If you don't have man pages for this extension, see + https://www.x.org/releases/current/doc/xextproto/shm.html + + (This document seems not to ever remain available on the web in one place + for very long; you can search for it by the title, "MIT-SHM -- The MIT + Shared Memory Extension".) + + To monitor the system's shared memory segments, run "ipcs -m". + */ + +#include "utils.h" + +/* #define DEBUG */ + +#include <errno.h> /* for perror() */ + +#ifdef HAVE_JWXYZ +# include "jwxyz.h" +#else +# include <X11/Xutil.h> /* for XDestroyImage() */ +#endif + +#include "xshm.h" +#include "resources.h" /* for get_string_resource() */ +#include "thread_util.h" /* for thread_malloc() */ + +#ifdef DEBUG +# include <X11/Xmu/Error.h> +#endif + +extern char *progname; + + +/* The documentation for the XSHM extension implies that if the server + supports XSHM but is not the local machine, the XShm calls will return + False; but this turns out not to be the case. Instead, the server + throws a BadAccess error. So, we need to catch X errors around all + of our XSHM calls, sigh. + */ + +#ifdef HAVE_XSHM_EXTENSION + +static Bool shm_got_x_error = False; +XErrorHandler old_handler = 0; +static int +shm_ehandler (Display *dpy, XErrorEvent *error) +{ + shm_got_x_error = True; + +#ifdef DEBUG + fprintf (stderr, "\n%s: ignoring X error from XSHM:\n", progname); + XmuPrintDefaultErrorMessage (dpy, error, stderr); + fprintf (stderr, "\n"); +#endif + + return 0; +} + + +#define CATCH_X_ERROR(DPY) do { \ + XSync((DPY), False); \ + shm_got_x_error = False; \ + if (old_handler != shm_ehandler) \ + old_handler = XSetErrorHandler (shm_ehandler); \ +} while(0) + +#define UNCATCH_X_ERROR(DPY) do { \ + XSync((DPY), False); \ + if (old_handler) \ + XSetErrorHandler (old_handler); \ + old_handler = 0; \ +} while(0) + +#endif /* HAVE_XSHM_EXTENSION */ + + +static void +print_error (int err) +{ + fprintf(stderr, "%s: %s\n", progname, strerror(err)); +} + +static XImage * +create_fallback (Display *dpy, Visual *visual, + unsigned int depth, + int format, XShmSegmentInfo *shm_info, + unsigned int width, unsigned int height) +{ + XImage *image = XCreateImage (dpy, visual, depth, format, 0, NULL, + width, height, BitmapPad(dpy), 0); + shm_info->shmid = -1; + + if (!image) { + print_error (ENOMEM); + } else { + /* Sometimes the XImage data needs to be aligned, such as for SIMD (SSE2 + in Fireworkx), or multithreading (AnalogTV). + */ + int error = thread_malloc ((void **)&image->data, dpy, + image->height * image->bytes_per_line); + if (error) { + print_error (error); + XDestroyImage (image); + image = NULL; + } else { + memset (image->data, 0, image->height * image->bytes_per_line); + } + } + + return image; +} + + +XImage * +create_xshm_image (Display *dpy, Visual *visual, + unsigned int depth, + int format, XShmSegmentInfo *shm_info, + unsigned int width, unsigned int height) +{ +#ifndef HAVE_XSHM_EXTENSION + + return create_fallback (dpy, visual, depth, format, shm_info, width, height); + +#else /* HAVE_XSHM_EXTENSION */ + + Status status; + XImage *image = 0; + if (!get_boolean_resource(dpy, "useSHM", "Boolean") || + !XShmQueryExtension (dpy)) { + return create_fallback (dpy, visual, depth, format, shm_info, + width, height); + } + + CATCH_X_ERROR(dpy); + image = XShmCreateImage(dpy, visual, depth, + format, NULL, shm_info, width, height); + UNCATCH_X_ERROR(dpy); + if (shm_got_x_error) + return create_fallback (dpy, visual, depth, format, shm_info, + width, height); + +#ifdef DEBUG + fprintf(stderr, "\n%s: XShmCreateImage(... %d, %d)\n", progname, + width, height); +#endif + + shm_info->shmid = shmget(IPC_PRIVATE, + image->bytes_per_line * image->height, + IPC_CREAT | 0777); +#ifdef DEBUG + fprintf(stderr, "%s: shmget(IPC_PRIVATE, %d, IPC_CREAT | 0777) ==> %d\n", + progname, image->bytes_per_line * image->height, shm_info->shmid); +#endif + + if (shm_info->shmid == -1) + { + char buf[1024]; + sprintf (buf, "%s: shmget failed", progname); + perror(buf); + XDestroyImage (image); + image = 0; + XSync(dpy, False); + } + else + { + shm_info->readOnly = False; + image->data = shm_info->shmaddr = shmat(shm_info->shmid, 0, 0); + +#ifdef DEBUG + fprintf(stderr, "%s: shmat(%d, 0, 0) ==> %d\n", progname, + shm_info->shmid, (int) image->data); +#endif + + CATCH_X_ERROR(dpy); + status = XShmAttach(dpy, shm_info); + UNCATCH_X_ERROR(dpy); + if (shm_got_x_error) + status = False; + + if (!status) + { + fprintf (stderr, "%s: XShmAttach failed!\n", progname); + XDestroyImage (image); + XSync(dpy, False); + shmdt (shm_info->shmaddr); + image = 0; + } +#ifdef DEBUG + else + fprintf(stderr, "%s: XShmAttach(dpy, shm_info) ==> True\n", progname); +#endif + + XSync(dpy, False); + + /* Delete the shared segment right now; the segment won't actually + go away until both the client and server have deleted it. The + server will delete it as soon as the client disconnects, so we + should delete our side early in case of abnormal termination. + (And note that, in the context of xscreensaver, abnormal + termination is the rule rather than the exception, so this would + leak like a sieve if we didn't do this...) + + #### Are we leaking anyway? Perhaps because of the window of + opportunity between here and the XShmAttach call above, during + which we might be killed? Do we need to establish a signal + handler for this case? + */ + shmctl (shm_info->shmid, IPC_RMID, 0); + +#ifdef DEBUG + fprintf(stderr, "%s: shmctl(%d, IPC_RMID, 0)\n\n", progname, + shm_info->shmid); +#endif + } + + if (!image) { + return create_fallback (dpy, visual, depth, format, shm_info, + width, height); + } + + return image; + +#endif /* HAVE_XSHM_EXTENSION */ +} + + +Bool +put_xshm_image (Display *dpy, Drawable d, GC gc, XImage *image, + int src_x, int src_y, int dest_x, int dest_y, + unsigned int width, unsigned int height, + XShmSegmentInfo *shm_info) +{ +#ifdef HAVE_XSHM_EXTENSION + assert (shm_info); /* Don't just s/XShmPutImage/put_xshm_image/. */ + if (shm_info->shmid != -1) { + /* XShmPutImage is asynchronous; the contents of the XImage must not be + modified until the server has placed the pixels on the screen and the + client has received an XShmCompletionEvent. Breaking this rule can cause + tearing. That said, put_xshm_image doesn't provide a send_event + parameter, so we're always breaking this rule. Not that it seems to + matter; everything (so far) looks fine without it. + + ####: Add a send_event parameter. And fake it for XPutImage. + */ + return XShmPutImage (dpy, d, gc, image, src_x, src_y, dest_x, dest_y, + width, height, False); + } +#endif /* HAVE_XSHM_EXTENSION */ + + return XPutImage (dpy, d, gc, image, src_x, src_y, dest_x, dest_y, + width, height); +} + + +Bool +get_xshm_image (Display *dpy, Drawable d, XImage *image, int x, int y, + unsigned long plane_mask, XShmSegmentInfo *shm_info) +{ +#ifdef HAVE_XSHM_EXTENSION + if (shm_info->shmid != -1) { + return XShmGetImage (dpy, d, image, x, y, plane_mask); + } +#endif /* HAVE_XSHM_EXTENSION */ + return XGetSubImage (dpy, d, x, y, image->width, image->height, plane_mask, + image->format, image, 0, 0) != NULL; +} + + +void +destroy_xshm_image (Display *dpy, XImage *image, XShmSegmentInfo *shm_info) +{ +#ifdef HAVE_XSHM_EXTENSION + if (shm_info->shmid == -1) { +#endif /* HAVE_XSHM_EXTENSION */ + + /* Don't let XDestroyImage free image->data. */ + thread_free (image->data); + image->data = NULL; + XDestroyImage (image); + return; + +#ifdef HAVE_XSHM_EXTENSION + } + + Status status; + + CATCH_X_ERROR(dpy); + status = XShmDetach (dpy, shm_info); + UNCATCH_X_ERROR(dpy); + if (shm_got_x_error) + status = False; + if (!status) + fprintf (stderr, "%s: XShmDetach failed!\n", progname); +#ifdef DEBUG + else + fprintf (stderr, "%s: XShmDetach(dpy, shm_info) ==> True\n", progname); +#endif + + XDestroyImage (image); + XSync(dpy, False); + + status = shmdt (shm_info->shmaddr); + + if (status != 0) + { + char buf[1024]; + sprintf (buf, "%s: shmdt(0x%lx) failed", progname, + (unsigned long) shm_info->shmaddr); + perror(buf); + } +#ifdef DEBUG + else + fprintf (stderr, "%s: shmdt(shm_info->shmaddr) ==> 0\n", progname); +#endif + + XSync(dpy, False); + +#endif /* HAVE_XSHM_EXTENSION */ +} |