add experimental iom API for multithreaded I/O multiplexing (in io.h)

CHANGES

@@ -4,6 +4,7 @@
   fix fmt_ip6 (Erwin Hoffmann)
   add MSG_ZEROCOPY support (only used for buffers >8k)
   use write in buffer_put for a slight perf improvement
+  add experimental iom API for multithreaded I/O multiplexing (in io.h)
 
 0.31:
   special case buffer_get_token with token length 1 through memccpy (almost 4x speedup)

io.h

@@ -144,6 +144,51 @@ int64 io_mmapwritefile(int64 out,int64 in,uint64 off,uint64 bytes,io_write_callb
  * aid in debugging the state machine if a descriptor loops or so */
 unsigned int io_debugstring(int64 s,char* buf,unsigned int bufsize);
 
+#ifdef __dietlibc__
+#include <threads.h>
+#else
+#include <pthread.h>
+#include <semaphore.h>
+#endif
+
+enum { SLOTS=128 };
+typedef struct iomux {
+  int ctx;
+  int working;	/* used to synchronize who is filling the queue */
+  unsigned int h,l; /* high, low */
+  struct {
+    int fd, events;
+  } q[SLOTS];
+#ifdef __dietlibc__
+  mtx_t mtx;
+  cnd_t sem;
+#else
+  sem_t sem;
+#endif
+} iomux_t;
+
+
+/* Init master context */
+int iom_init(iomux_t* c);
+
+/* Add socket to iomux */
+enum {
+  IOM_READ=1,
+  IOM_WRITE=2,
+  IOM_ERROR=4
+};
+/* return -1 if error, or | of IOM_READ, IOM_WRITE or IOM_ERROR */
+int iom_add(iomux_t* c,int64 s,unsigned int events);
+
+/* Blocking wait for single event, timeout in milliseconds */
+/* return -1 if error, 0 if ok; s set to fd, revents set to known events on that fd */
+/* when done with the fd, call iom_add on it again! */
+/* This can be called by multiple threads in parallel */
+int iom_wait(iomux_t* c,int64* s,unsigned int* revents,unsigned long timeout);
+
+/* Call this to terminate all threads waiting in iom_wait */
+int iom_abort(iomux_t* c);
+
 #ifdef __cplusplus
 }
 #endif

io/iom_abort.3

@@ -0,0 +1,19 @@
+.TH iom_abort 3
+.SH NAME
+iom_abort \- abort all pending iom_wait calls
+.SH SYNTAX
+.B #include <libowfat/io.h>
+
+int \fBiom_abort\fP(iomux_t* c);
+.SH DESCRIPTION
+\fIiom_abort\fR will cause all currently running instances of
+\fIiom_wait\fR to return immediately with return value -2.
+
+.SH "LINKING"
+You may have to add \fI-lpthread\fR to the command line in the linking
+step.
+
+.SH "RETURN VALUE"
+iom_abort returns 0 on success and -1 on error, setting errno.
+.SH "SEE ALSO"
+iom_init, iom_add, iom_wait

io/iom_abort.c

@@ -0,0 +1,10 @@
+#include "io_internal.h"
+
+int iom_abort(iomux_t* c) {
+  c->working=-2;
+#ifdef __dietlibc__
+  return cnd_broadcast(&c->sem);
+#else
+  return sem_post(&c->sem);
+#endif
+}

io/iom_add.3

@@ -0,0 +1,33 @@
+.TH iom_add 3
+.SH NAME
+iom_add \- add event to I/O multiplexer
+.SH SYNTAX
+.B #include <libowfat/io.h>
+
+int \fBiom_add\fP(iomux_t* c, int64 fd, unsigned int events);
+.SH DESCRIPTION
+iom_add adds an event you are interested in to an I/O multiplexer.
+
+\fIfd\fR is the file descriptor (usually a socket) you are interested
+in, and \fIevents\fR is the operation you want to do. It can be IOM_READ
+or IOM_WRITE.
+
+If that operation becomes possible on that descriptor, and some thread
+is calling \fIiom_wait\fR at the time, it will return and tell you the
+fd and the event.
+
+Note that the event registration is removed from the iomux_t context if
+it occurs. You will have to call \fIiom_wait\fR again after you handled
+the event, if you are still interested in it.
+
+Closing a file descriptor with registered events will discard the event
+registration.
+
+.SH "LINKING"
+You may have to add \fI-lpthread\fR to the command line in the linking
+step.
+
+.SH "RETURN VALUE"
+iom_add returns 0 on success and -1 on error, setting errno.
+.SH "SEE ALSO"
+iom_init, iom_wait, iom_abort

io/iom_add.c

@@ -0,0 +1,28 @@
+#include "io_internal.h"
+#ifdef HAVE_EPOLL
+#include <sys/epoll.h>
+#endif
+#ifdef HAVE_KQUEUE
+#include <sys/types.h>
+#include <sys/event.h>
+#include <sys/time.h>
+#endif
+
+int iom_add(iomux_t* c,int64 s,unsigned int events) {
+#ifdef HAVE_EPOLL
+  struct epoll_event e = { .events=EPOLLONESHOT, .data.fd=s };
+  if (events & IOM_READ) e.events|=EPOLLIN;
+  if (events & IOM_WRITE) e.events|=EPOLLOUT;
+  return epoll_ctl(c->ctx, EPOLL_CTL_ADD, s, &e);
+#elif defined(HAVE_KQUEUE)
+  struct kevent kev;
+  struct timespec ts = { 0 };
+  EV_SET(&kev, s,
+	 (events & IOM_READ ? EVFILT_READ : 0) +
+	 (events & IOM_WRITE ? EVFILT_WRITE : 0),
+	 EV_ADD | EV_ENABLE | EV_ONESHOT, 0, 0, (void*)s);
+  return kevent(c->ctx, &kev, 1, 0, 0, &ts);
+#else
+#warning "only epoll and kqueue supported for now"
+#endif
+}

io/iom_init.3

@@ -0,0 +1,30 @@
+.TH iom_init 3
+.SH NAME
+iom_init \- create new I/O multiplexer
+.SH SYNTAX
+.B #include <libowfat/io.h>
+
+int \fBiom_init\fP(iomux_t* c);
+.SH DESCRIPTION
+iom_init initializes an I/O multiplexer.
+
+An I/O multiplexer is a context that can be used to do I/O multiplexing
+with support for multiple threads. Add events to a multiplexer using
+\fIiom_add\fR, and then get the next available event with
+\fIiom_wait\fR. If you are done and want to signal all the threads
+something, set a volatile global variable to tell the threads to stop
+and then fall \fIiom_abort\fR to tell all pending iom_wait operations in
+all threads to return immediately.
+
+After \fIiom_init\fR is done, \fIiom_add\fR and \fIiom_wait\fR can be
+called from different threads on the same context, and they will
+synchronize internally.
+
+.SH "LINKING"
+You may have to add \fI-lpthread\fR to the command line in the linking
+step.
+
+.SH "RETURN VALUE"
+iom_init returns 0 on success and -1 on error, setting errno.
+.SH "SEE ALSO"
+iom_add, iom_wait, iom_abort

io/iom_init.c

@@ -0,0 +1,38 @@
+#include "io_internal.h"
+#ifdef HAVE_EPOLL
+#include <sys/epoll.h>
+#endif
+#ifdef HAVE_KQUEUE
+#include <sys/types.h>
+#include <sys/event.h>
+#include <sys/time.h>
+#endif
+
+int iom_init(iomux_t* c) {
+#ifdef HAVE_EPOLL
+  c->ctx = epoll_create1(EPOLL_CLOEXEC);
+#elif defined(HAVE_KQUEUE)
+  if ((c->ctx = kqueue()) != -1) {
+    if (fcntl(c->ctx,F_SETFD,FD_CLOEXEC) == -1) {
+      close(c->ctx);
+      c->ctx=-1;
+    }
+  }
+#else
+#warning "only epoll and kqueue supported for now"
+#endif
+  unsigned int i;
+  c->working=0;
+  c->h=c->l=0;	/* no elements in queue */
+  for (i=0; i<SLOTS; ++i) {
+    c->q[i].fd=-1;
+    c->q[i].events=0;
+  }
+#ifdef __dietlibc__
+  mtx_init(&c->mtx, mtx_timed);
+  cnd_init(&c->sem);
+#else
+  sem_init(&c->sem, 0, 1);
+#endif
+  return (c->ctx!=-1);
+}

io/iom_wait.3

@@ -0,0 +1,38 @@
+.TH iom_wait 3
+.SH NAME
+iom_wait \- wait for event from I/O multiplexer
+.SH SYNTAX
+.B #include <libowfat/io.h>
+
+int \fBiom_wait\fP(iomux_t* c,
+                   int64* fd, unsigned int* events,
+		   unsigned long timeout);
+.SH DESCRIPTION
+iom_wait will wait for events registered to the I/O multiplexer with
+\fIiom_add\fR. It will wait \fItimeout\fR milliseconds.
+
+If during that time any of the registered events occur, \fIiom_wait\fR
+will set \fIfd\fR to the file descriptor the event happened on, and
+\fIevents\fR to the sum of IOM_READ, IOM_WRITE and IOM_ERROR, depending
+on what event actually happened, and return 1.
+
+If nothing happens during that time, it will return 0 and leave \fIfd\fR
+and \fIevents\fR alone.
+
+Note that the event registration is removed from the iomux_t context if
+it occurs. You will have to call \fIiom_wait\fR again after you handled
+the event, if you are still interested in it.
+
+Closing a file descriptor with registered events will discard the event
+registration.
+
+.SH "LINKING"
+You may have to add \fI-lpthread\fR to the command line in the linking
+step.
+
+.SH "RETURN VALUE"
+iom_wait returns 1 on success, 0 if there was a timeout, and -1 on
+error, setting errno. If \fIiom_abort\fR was called on the I/O
+multiplexer context, it will return -2.
+.SH "SEE ALSO"
+iom_init, iom_add, iom_abort

io/iom_wait.c

@@ -0,0 +1,124 @@
+#include "io_internal.h"
+#ifdef HAVE_EPOLL
+#include <sys/epoll.h>
+#endif
+#ifdef HAVE_KQUEUE
+#include <sys/types.h>
+#include <sys/event.h>
+#include <sys/time.h>
+#endif
+#include <errno.h>
+
+int iom_wait(iomux_t* c,int64* s,unsigned int* revents,unsigned long timeout) {
+  for (;;) {
+    /* If we have an event in the queue, use that one */
+    int r;
+    if (c->working==-2) return -2;	/* iomux was aborted */
+    for (;;) {
+      unsigned int f=c->l;
+      if (f == c->h)
+	break; /* no elements in queue */
+      int n=(f+1)%SLOTS;
+      if (__sync_bool_compare_and_swap(&c->l,f,n)) {
+	/* we got one, and its index is in f */
+	*s=c->q[f].fd;
+	*revents=c->q[f].events;
+      }
+      /* collided with another thread, try again */
+    }
+    /* The queue was empty. If someone else is already calling
+    * epoll_wait/kevent, then use the semaphore */
+    if (__sync_bool_compare_and_swap(&c->working,0,1)) {
+      /* we have the job to fill the struct. */
+      int freeslots = (c->h - c->l);
+      if (!freeslots) freeslots=SLOTS;
+
+#ifdef HAVE_EPOLL
+      struct epoll_event ee[SLOTS];
+      int i;
+      r=epoll_wait(c->ctx, ee, freeslots, timeout);
+      if (r<=0) {
+	/* we ran into a timeout, so let someone else take over */
+	c->working=0;
+#ifdef __dietlibc__
+	cnd_broadcast(&c->sem);
+#else
+	sem_post(&c->sem);
+#endif
+	return r;
+      }
+      for (i=0; i<r; ++i) {
+	/* convert events */
+	int e = ((ee[i].events & (EPOLLIN|EPOLLHUP|EPOLLERR)) ? IOM_READ : 0) |
+	        ((ee[i].events & (EPOLLOUT|EPOLLHUP|EPOLLERR)) ? IOM_WRITE : 0) |
+	        ((ee[i].events & EPOLLERR) ? IOM_ERROR : 0);
+	if (i+1==r) {
+	  /* return last event instead of enqueueing it */
+	  *s=ee[i].data.fd;
+	  *revents=e;
+	} else {
+	  c->q[c->h].fd=ee[i].data.fd;
+	  c->q[c->h].events=e;
+	  c->h = (c->h + 1) % SLOTS;
+	}
+      }
+#elif defined(HAVE_KQUEUE)
+      struct kevent kev[SLOTS];
+      struct timespec ts = { .tv_sec=timeout/1000, .tv_nsec=(timeout%1000)*1000000 };
+      int r=kevent(c->ctx, 0, 0, &kev, freeslots, &ts);
+      if (r<=0) {
+	/* we ran into a timeout, so let someone else take over */
+	c->working=0;
+#ifdef __dietlibc__
+	cnd_broadcast(&c->sem);
+#else
+	sem_post(&c->sem);
+#endif
+	return r;
+      }
+      for (i=0; i<r; ++i) {
+	/* convert events */
+	int e = (kev[i].filter == EVFILT_READ ? IOM_READ : 0) |
+	        (kev[i].filter == EVFILT_WRITE ? IOM_WRITE : 0);
+	if (i+1==r) {
+	  /* return last event instead of enqueueing it */
+	  *s=kev.ident;
+	  *revents=e;
+	} else {
+	  c->q[c->h].fd=kev[i].ident;
+	  c->q[c->h].events=e;
+	  c->h = (c->h + 1) % SLOTS;
+	}
+      }
+#else
+#warning "only epoll and kqueue supported for now"
+#endif
+      /* We need to signal the other threads.
+	 Either there are other events left, or we need one of them to
+	 wake up and call epoll_wait/kevent next, because we aren't
+	 doing it anymore */
+      c->working=0;
+#ifdef __dietlibc__
+      cnd_signal(&c->sem);
+#else
+      sem_post(&c->sem);
+#endif
+      return 1;
+    } else {
+      /* somebody else has the job to fill the queue */
+      struct timespec ts;
+      ts.tv_sec = timeout / 1000;
+      ts.tv_nsec = (timeout % 1000) * 1000000;
+#ifdef __dietlibc__
+      r=cnd_timedwait(&c->sem,&c->mtx,&ts);
+#else
+      r=sem_timedwait(&c->sem,&ts);
+#endif
+      if (r==-1) {
+	if (errno==ETIMEDOUT) return 0;
+	return -1;
+      }
+      /* fall through into next loop iteration */
+    }
+  }
+}