Add unix signal integration with the iomux

src/iomux_signal.c

@@ -0,0 +1,279 @@
+#include <pthread.h>
+#include <string.h>
+#include <stdint.h>
+#include <signal.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <assert.h>
+#include <unistd.h>
+#include "ucore/tailq.h"
+#include "ucore/fd_utils.h"
+#include "ucore/iomux_signal.h"
+
+/* Integrating of unix signals (man 7 signal) with
+ * an IOMux event loop.
+ * This is done by setting up a pipe, registring a handler with
+ * the IOMux to handle the read end to that pipe, and writing
+ * the signal number to that pipe in the signal handler.
+ *
+ * Currently the signal number is treated as an uint8_t to avoid
+ * dealing with the extremely unlikely case of partial writes in
+ * a signal handler. Currently this is more than enough for the max value of
+ * signals on linux at least.
+ *
+ */
+
+struct IOMuxSignalEntry {
+    struct TailQ entry; //within SignalData.head
+    int signo;
+    IOMuxSignalHandler callback;
+    void *cookie;
+    struct sigaction old_sa;
+};
+
+struct SignalData {
+    struct TailQ head; //of IOMuxSignalEntry
+    struct IOMuxFD fd;
+    int pipes[2];
+    struct IOMux *mux;
+    int initialized;
+};
+
+static pthread_mutex_t g_signal_lock = PTHREAD_MUTEX_INITIALIZER;
+
+//protected by g_signal_lock
+struct SignalData g_signal_global;
+
+static inline void uc_signal_lock(void)
+{
+    int rc = pthread_mutex_lock(&g_signal_lock);
+    assert(rc == 0);
+}
+
+static inline void uc_signal_unlock(void)
+{
+    int rc = pthread_mutex_unlock(&g_signal_lock);
+    assert(rc == 0);
+}
+
+//call with lock held
+static struct IOMuxSignalEntry *uc_find_signal_entry(int signo)
+{
+    struct IOMuxSignalEntry *it;
+
+    UC_TAILQ_FOREACH_CONTAINER(it, entry, &g_signal_global.head) {
+        if (it->signo == signo) {
+            return it;
+        }
+    }
+
+    return NULL;
+}
+
+//call with lock held
+static void uc_deinitailize_iomux_signals(void)
+{
+    assert(g_signal_global.mux != NULL);
+    assert(g_signal_global.initialized == 1);
+    assert(uc_tailq_empty(&g_signal_global.head));
+
+    iomux_unregister_fd(g_signal_global.mux, &g_signal_global.fd);
+
+    close(g_signal_global.pipes[0]);
+    close(g_signal_global.pipes[1]);
+
+    g_signal_global.mux = NULL; 
+    g_signal_global.initialized = 0; 
+    g_signal_global.fd.callback = NULL;
+    g_signal_global.fd.fd = -1;
+}
+
+//IOMux fd callback, which dispatches the signal to the registered handler
+static void uc_iomux_signal_cb(struct IOMux *mux, struct IOMuxFD *fd, unsigned int events)
+{
+
+    uint8_t signo;
+    ssize_t rc;
+    struct IOMuxSignalEntry *entry = NULL;
+
+    uc_signal_lock();
+
+    rc = read(fd->fd, &signo, 1);
+    if (rc == 1) {
+        entry = uc_find_signal_entry(signo);
+    }
+
+    assert(rc != -1 || errno == EWOULDBLOCK);
+
+    //need to unlock here, otherwise we deadlock if the callback
+    //registers/unregisters a signal
+    uc_signal_unlock();
+
+    if (entry != NULL) {
+        entry->callback(mux, signo, entry->cookie);
+        //note don't touch entry after this, the callback might
+        //have unregistered itself
+    }
+}
+
+//unix signal handler
+static void uc_global_signal_handler(int signo)
+{
+    uint8_t data = signo;
+    int save_errno = errno;
+
+    write(g_signal_global.pipes[1], &data, 1);
+
+    errno = save_errno;
+}
+
+//call with lock held
+static int uc_initailize_iomux_signals(struct IOMux *mux)
+{
+    int rc = 0;
+
+    assert(g_signal_global.mux == NULL);
+    assert(g_signal_global.initialized == 0);
+
+    rc = pipe(g_signal_global.pipes);
+    if (rc != 0) {
+        return errno;
+    }
+    
+    uc_set_nonblocking(g_signal_global.pipes[0]);
+    uc_set_nonblocking(g_signal_global.pipes[1]);
+
+    uc_tailq_init(&g_signal_global.head);
+
+    g_signal_global.mux         = mux;
+    g_signal_global.fd.fd       = g_signal_global.pipes[0];
+    g_signal_global.fd.what     = MUX_EV_READ;
+    g_signal_global.fd.callback = uc_iomux_signal_cb;
+
+    rc = iomux_register_fd(mux, &g_signal_global.fd);
+    if (rc == 0) {
+        g_signal_global.initialized = 1; 
+    } else {
+        uc_deinitailize_iomux_signals();
+    }
+
+    return rc;
+}
+
+static struct IOMuxSignalEntry *uc_signal_entry_new(int signo,
+                                            IOMuxSignalHandler handler,
+                                            void *cookie)
+{
+   struct IOMuxSignalEntry *entry;
+   
+   entry = calloc(1, sizeof *entry);
+   if (entry == NULL) {
+       return NULL;
+   }
+
+   entry->signo    = signo;
+   entry->callback = handler;
+   entry->cookie   = cookie;
+
+   return entry;
+}
+
+
+static int iomux_register_unixsignal_internal(struct IOMux *mux, 
+                      int signo, 
+                      IOMuxSignalHandler handler, 
+                      void *cookie)
+{
+    struct IOMuxSignalEntry *entry;
+    int rc;
+    struct sigaction sa;
+
+    if (!g_signal_global.initialized) {
+        rc = uc_initailize_iomux_signals(mux);
+        if (rc != 0) {
+            return rc;
+        }
+    }
+
+    //Only one mux can handle signals
+    if (g_signal_global.mux != mux) {
+        return EINVAL;
+    }
+
+    entry = uc_find_signal_entry(signo);
+    if (entry != NULL) {
+        return EEXIST;
+    }
+
+    entry = uc_signal_entry_new(signo, handler, cookie);
+    if (entry == NULL) {
+        return ENOMEM;
+    }
+
+    memset(&sa, 0, sizeof sa);
+    sa.sa_handler = uc_global_signal_handler;
+    sa.sa_flags = SA_RESTART;
+    sigfillset(&sa.sa_mask);
+
+    rc = sigaction(signo, &sa, &entry->old_sa);
+    if (rc == 0) {
+        uc_tailq_insert_tail(&g_signal_global.head, &entry->entry);
+    } else {
+        rc = errno;
+        free(entry);
+    }
+
+   return rc;
+}
+
+int iomux_register_unixsignal(struct IOMux *mux, 
+                      int signo, 
+                      IOMuxSignalHandler handler, 
+                      void *cookie)
+{
+    int rc;
+
+    uc_signal_lock();
+    
+    rc = iomux_register_unixsignal_internal(mux, signo, handler, cookie);
+
+    if (g_signal_global.initialized && uc_tailq_empty(&g_signal_global.head)) {
+        //we might have initialized the iomux but otherwise failed
+        uc_deinitailize_iomux_signals();
+    }
+
+    uc_signal_unlock();
+
+    return rc;
+}
+
+int iomux_unregister_unixsignal(struct IOMux *mux, int signo)
+{
+    struct IOMuxSignalEntry *entry;
+    int rc = ENOENT;
+
+    uc_signal_lock();
+    
+    if (!g_signal_global.initialized || g_signal_global.mux != mux) {
+        uc_signal_unlock();
+        return EINVAL;
+    }
+
+
+    entry = uc_find_signal_entry(signo);
+    if (entry != NULL) {
+        uc_tailq_remove(&entry->entry);
+        rc = sigaction(entry->signo, &entry->old_sa, NULL);
+        assert(rc == 0);
+        free(entry);
+    }
+
+    if (uc_tailq_empty(&g_signal_global.head)) {
+        uc_deinitailize_iomux_signals();
+    }
+
+    uc_signal_unlock();
+
+    return 0;
+}
+