Branch imports for masters.

Copied from Perforce
 Change: 23678
 ServerID: perforce.ravenbrook.com

1 files changed, 1526 insertions, 0 deletions

diff --git a/mps/code/buffer.c b/mps/code/buffer.c
new file mode 100644
index 00000000000..22b4cda9485
--- /dev/null
+++ b/mps/code/buffer.c
@@ -0,0 +1,1526 @@
+/* impl.c.buffer: ALLOCATION BUFFER IMPLEMENTATION
+ *
+ * $HopeName: MMsrc!buffer.c(trunk.63) $
+ * Copyright (C) 2000 Harlequin Limited.  All rights reserved.
+ *
+ * .purpose: This is (part of) the implementation of allocation buffers.
+ * Several macros which also form part of the implementation are in
+ * impl.h.mps.  Several macros forming part of impl.h.mps should be
+ * consistent with the macros and functions in this module.
+ *
+ * DESIGN
+ *
+ * .design: See design.mps.buffer.
+ *
+ * .ap.async: The mutator is allowed to change certain AP fields
+ * asynchronously.  Functions that can be called on buffers not
+ * synchronized with the mutator must take care when reading these
+ * fields.  Such functions are marked with this tag.
+ *
+ * TRANSGRESSIONS
+ *
+ * .trans.mod: There are several instances where pool structures are
+ * directly accessed by this module because impl.c.pool does not provide
+ * an adequate (or adequately documented) interface.  They bear this
+ * tag.  */
+
+#include "mpm.h"
+
+SRCID(buffer, "$HopeName: MMsrc!buffer.c(trunk.63) $");
+
+
+/* forward declarations */
+static void BufferFrameNotifyPopPending(Buffer buffer);
+
+
+/* BufferCheck -- check consistency of a buffer
+ *
+ * See .ap.async.  */
+
+Bool BufferCheck(Buffer buffer)
+{
+  CHECKS(Buffer, buffer);
+  CHECKL(buffer->serial < buffer->pool->bufferSerial); /* .trans.mod */
+  CHECKU(Arena, buffer->arena);
+  CHECKU(Pool, buffer->pool);
+  CHECKL(buffer->arena == buffer->pool->arena);
+  CHECKL(RingCheck(&buffer->poolRing)); /* design.mps.check.type.no-sig */
+  CHECKL(BoolCheck(buffer->isMutator));
+  CHECKL(buffer->fillSize >= 0.0);
+  CHECKL(buffer->emptySize >= 0.0);
+  CHECKL(buffer->emptySize <= buffer->fillSize);
+  CHECKL(buffer->alignment == buffer->pool->alignment);
+  CHECKL(AlignCheck(buffer->alignment));
+  CHECKL(BoolCheck(buffer->apStruct.enabled));
+
+  if (buffer->apStruct.enabled) {
+    /* no useful check for frameptr - mutator may be updating it */
+    CHECKL(BoolCheck(buffer->apStruct.lwPopPending));
+  } else {
+    CHECKL(buffer->apStruct.lwPopPending == FALSE);
+    CHECKL(buffer->apStruct.frameptr == NULL);
+  }
+
+  /* If any of the buffer's fields indicate that it is reset, make */
+  /* sure it is really reset.  Otherwise, check various properties */
+  /* of the non-reset fields. */
+  if (buffer->mode & BufferModeTRANSITION) {
+    /* nothing to check */
+  } else if ((buffer->mode & BufferModeATTACHED) == 0
+             || buffer->base == (Addr)0
+             || buffer->apStruct.init == (Addr)0
+             || buffer->apStruct.alloc == (Addr)0
+             || buffer->poolLimit == (Addr)0) {
+    CHECKL((buffer->mode & BufferModeATTACHED) == 0);
+    CHECKL(buffer->base == (Addr)0);
+    CHECKL(buffer->initAtFlip == (Addr)0);
+    CHECKL(buffer->apStruct.init == (Addr)0);
+    CHECKL(buffer->apStruct.alloc == (Addr)0);
+    CHECKL(buffer->apStruct.limit == (Addr)0);
+    /* Nothing reliable to check for lightweight frame state */
+    CHECKL(buffer->poolLimit == (Addr)0);
+  } else {
+    Addr aplimit; 
+
+    /* The buffer is attached to a region of memory.   */
+    /* Check consistency. */
+    CHECKL(buffer->mode & BufferModeATTACHED);
+
+    /* These fields should obey the ordering */
+    /* base <= init <= alloc <= poolLimit */
+    CHECKL(buffer->base <= buffer->apStruct.init);
+    CHECKL(buffer->apStruct.init <= buffer->apStruct.alloc);
+    CHECKL(buffer->apStruct.alloc <= buffer->poolLimit);
+
+    /* Check that the fields are aligned to the buffer alignment. */
+    CHECKL(AddrIsAligned(buffer->base, buffer->alignment));
+    CHECKL(AddrIsAligned(buffer->initAtFlip, buffer->alignment));
+    CHECKL(AddrIsAligned(buffer->apStruct.init, buffer->alignment));
+    CHECKL(AddrIsAligned(buffer->apStruct.alloc, buffer->alignment));
+    CHECKL(AddrIsAligned(buffer->apStruct.limit, buffer->alignment));
+    CHECKL(AddrIsAligned(buffer->poolLimit, buffer->alignment));
+
+    /* .lwcheck: If LW frames are enabled, the buffer may become */
+    /* trapped asynchronously. It can't become untrapped */
+    /* asynchronously, though. See design.mps.alloc-frame.lw-frame.pop. */
+    /* Read a snapshot value of the limit field. Use this to determine */
+    /* if we are trapped, and to permit more useful checking when not */
+    /* yet trapped. */
+    aplimit = buffer->apStruct.limit;
+
+    /* If the buffer isn't trapped then "limit" should be the limit */
+    /* set by the owning pool.  Otherwise, "init" is either at the */
+    /* same place it was at flip (.commit.before) or has been set */
+    /* to "alloc" (.commit.after).  Also, when the buffer is */
+    /* flipped, initAtFlip should hold the init at flip, which is */
+    /* between the base and current init.  Otherwise, initAtFlip */
+    /* is kept at zero to avoid misuse (see */
+    /* request.dylan.170429.sol.zero). */
+
+    if ((buffer->apStruct.enabled && aplimit == (Addr)0) /* see .lwcheck */
+        || (!buffer->apStruct.enabled && BufferIsTrapped(buffer))) {
+      /* .check.use-trapped: This checking function uses BufferIsTrapped, */
+      /* So BufferIsTrapped can't do checking as that would cause an */
+      /* infinite loop. */
+      CHECKL(aplimit == (Addr)0);
+      if (buffer->mode & BufferModeFLIPPED) {
+        CHECKL(buffer->apStruct.init == buffer->initAtFlip
+               || buffer->apStruct.init == buffer->apStruct.alloc);
+        CHECKL(buffer->base <= buffer->initAtFlip);
+        CHECKL(buffer->initAtFlip <= buffer->apStruct.init);
+      }
+      /* Nothing special to check in the logged mode. */
+    } else {
+      CHECKL(aplimit == buffer->poolLimit); /* see .lwcheck */
+      CHECKL(buffer->initAtFlip == (Addr)0);
+    }
+  }
+
+  return TRUE;
+}
+
+
+/* BufferDescribe -- write out description of buffer
+ *
+ * See impl.h.mpmst for structure definitions.  */
+
+Res BufferDescribe(Buffer buffer, mps_lib_FILE *stream)
+{
+  Res res;
+
+  if (!CHECKT(Buffer, buffer)) return ResFAIL;
+  if (stream == NULL) return ResFAIL;
+
+  res = WriteF(stream,
+               "Buffer $P ($U) {\n",
+               (WriteFP)buffer, (WriteFU)buffer->serial,
+               "  class $P (\"$S\")\n", 
+               (WriteFP)buffer->class, buffer->class->name,
+               "  Arena $P\n",       (WriteFP)buffer->arena,
+               "  Pool $P\n",        (WriteFP)buffer->pool,
+               buffer->isMutator ?
+                 "  Mutator Buffer\n" : "  Internal Buffer\n",
+               "  Mode $B\n",        (WriteFB)(buffer->mode),
+               "  fillSize $UKb\n",  (WriteFU)(buffer->fillSize / 1024),
+               "  emptySize $UKb\n", (WriteFU)(buffer->emptySize / 1024),
+               "  alignment $W\n",   (WriteFW)buffer->alignment,
+               "  base $A\n",        buffer->base,
+               "  initAtFlip $A\n",  buffer->initAtFlip,
+               "  init $A\n",        buffer->apStruct.init,
+               "  alloc $A\n",       buffer->apStruct.alloc,
+               "  limit $A\n",       buffer->apStruct.limit,
+               "  poolLimit $A\n",   buffer->poolLimit,
+               NULL);
+  if (res != ResOK) return res;
+
+  res = buffer->class->describe(buffer, stream);
+  if (res != ResOK) return res;
+
+  res = WriteF(stream, "} Buffer $P ($U)\n",
+               (WriteFP)buffer, (WriteFU)buffer->serial,
+               NULL);
+  return res;
+}
+
+
+/* BufferInitV -- initialize an allocation buffer */
+
+static Res BufferInitV(Buffer buffer, BufferClass class,
+                       Pool pool, Bool isMutator, va_list args)
+{
+  Arena arena;
+  Res res;
+
+  AVER(buffer != NULL);
+  AVERT(BufferClass, class);
+  AVERT(Pool, pool);
+  /* The PoolClass should support buffer protocols */
+  AVER((pool->class->attr & AttrBUF)); /* .trans.mod */
+  
+  arena = PoolArena(pool);
+  /* Initialize the buffer.  See impl.h.mpmst for a definition of */
+  /* the structure.  sig and serial comes later .init.sig-serial */
+  buffer->arena = arena;
+  buffer->class = class;
+  buffer->pool = pool;
+  RingInit(&buffer->poolRing);
+  buffer->isMutator = isMutator;
+  if (ArenaGlobals(arena)->bufferLogging) {
+    buffer->mode = BufferModeLOGGED;
+  } else {
+    buffer->mode = 0;
+  }
+  buffer->fillSize = 0.0;
+  buffer->emptySize = 0.0;
+  buffer->alignment = pool->alignment; /* .trans.mod */
+  buffer->base = (Addr)0;
+  buffer->initAtFlip = (Addr)0;
+  buffer->apStruct.init = (Addr)0;
+  buffer->apStruct.alloc = (Addr)0;
+  buffer->apStruct.limit = (Addr)0;
+  buffer->apStruct.frameptr = NULL;
+  buffer->apStruct.enabled = FALSE;
+  buffer->apStruct.lwPopPending = FALSE;
+  buffer->poolLimit = (Addr)0;
+  buffer->rampCount = 0;
+
+  /* .init.sig-serial: Now the vanilla stuff is initialized, */
+  /* sign the buffer and give it a serial number. It can */
+  /* then be safely checked in subclass methods. */
+  buffer->sig = BufferSig;
+  buffer->serial = pool->bufferSerial; /* .trans.mod */
+  ++pool->bufferSerial;
+  AVERT(Buffer, buffer);
+
+  /* Dispatch to the buffer class method to perform any  */
+  /* class-specific initialization of the buffer. */
+  res = (*class->init)(buffer, pool, args);
+  if (res != ResOK)
+    goto failInit;
+
+  /* Attach the initialized buffer to the pool. */
+  RingAppend(&pool->bufferRing, &buffer->poolRing);
+
+  return ResOK;
+
+failInit:
+  RingFinish(&buffer->poolRing);
+  buffer->sig = SigInvalid;
+  return res;
+}
+
+
+/* BufferCreate -- create an allocation buffer
+ *
+ * See design.mps.buffer.method.create.  */
+
+Res BufferCreate(Buffer *bufferReturn, BufferClass class, 
+                 Pool pool, Bool isMutator, ...)
+{
+  Res res;
+  va_list args;
+
+  va_start(args, isMutator);
+  res = BufferCreateV(bufferReturn, class, pool, isMutator, args);
+  va_end(args);
+  return res;
+}
+
+
+/* BufferCreateV -- create an allocation buffer, with varargs
+ *
+ * See design.mps.buffer.method.create.  */
+
+Res BufferCreateV(Buffer *bufferReturn, BufferClass class, 
+                  Pool pool, Bool isMutator, va_list args)
+{
+  Res res;
+  Buffer buffer;
+  Arena arena;
+  void *p;
+
+  AVER(bufferReturn != NULL);
+  AVERT(BufferClass, class);
+  AVERT(Pool, pool);
+
+  arena = PoolArena(pool);
+
+  /* Allocate memory for the buffer descriptor structure. */
+  res = ControlAlloc(&p, arena, class->size, 
+                     /* withReservoirPermit */ FALSE);
+  if (res != ResOK)
+    goto failAlloc;
+  buffer = p;
+
+  /* Initialize the buffer descriptor structure. */
+  res = BufferInitV(buffer, class, pool, isMutator, args);
+  if (res != ResOK)
+    goto failInit;
+
+  *bufferReturn = buffer;
+  return ResOK;
+
+failInit:
+  ControlFree(arena, buffer, class->size);
+failAlloc:
+  return res;
+}
+
+
+/* BufferDetach -- detach a buffer from a region  */
+
+void BufferDetach(Buffer buffer, Pool pool)
+{
+  AVERT(Buffer, buffer);
+  AVER(BufferIsReady(buffer));
+
+  if (!BufferIsReset(buffer)) {
+    Addr init, limit;
+    Size spare;
+
+    buffer->mode |= BufferModeTRANSITION;
+    init = buffer->apStruct.init;
+    limit = buffer->poolLimit;
+    /* Ask the owning pool to do whatever it needs to before the */
+    /* buffer is detached (e.g. copy buffer state into pool state). */
+    (*pool->class->bufferEmpty)(pool, buffer, init, limit);
+    /* Use of lightweight frames must have been disabled by now */
+    AVER(BufferFrameState(buffer) == BufferFrameDISABLED);
+
+    /* run any class-specific detachment method */
+    buffer->class->detach(buffer);
+
+    spare = AddrOffset(init, limit);
+    buffer->emptySize += spare;
+    if (buffer->isMutator) {
+      buffer->pool->emptyMutatorSize += spare;
+      ArenaGlobals(buffer->arena)->emptyMutatorSize += spare;
+      ArenaGlobals(buffer->arena)->allocMutatorSize +=
+        AddrOffset(buffer->base, init);
+    } else {
+      buffer->pool->emptyInternalSize += spare;
+      ArenaGlobals(buffer->arena)->emptyInternalSize += spare;
+    }
+
+    /* Reset the buffer. */
+    buffer->base = (Addr)0;
+    buffer->initAtFlip = (Addr)0;
+    buffer->apStruct.init = (Addr)0;
+    buffer->apStruct.alloc = (Addr)0;
+    buffer->apStruct.limit = (Addr)0;
+    buffer->poolLimit = (Addr)0;
+    buffer->mode &=
+      ~(BufferModeATTACHED|BufferModeFLIPPED|BufferModeTRANSITION);
+    BufferFrameSetState(buffer, BufferFrameDISABLED);
+
+    EVENT_PW(BufferEmpty, buffer, spare);
+  }
+}
+
+
+/* BufferDestroy -- destroy an allocation buffer
+ *
+ * See design.mps.buffer.method.destroy.  */
+
+void BufferDestroy(Buffer buffer)
+{
+  Arena arena;
+  BufferClass class;
+
+  AVERT(Buffer, buffer);
+  arena = buffer->arena;
+  class = buffer->class;
+  AVERT(BufferClass, class);
+  BufferFinish(buffer);
+  ControlFree(arena, buffer, class->size);
+}
+
+
+/* BufferFinish -- finish an allocation buffer */
+
+void BufferFinish(Buffer buffer)
+{
+  Pool pool;
+
+  AVERT(Buffer, buffer);
+
+  pool = BufferPool(buffer);
+
+  /* The PoolClass should support buffer protocols */
+  AVER((pool->class->attr & AttrBUF)); /* .trans.mod */
+  AVER(BufferIsReady(buffer));
+
+  /* design.mps.alloc-frame.lw-frame.sync.trip */
+  if (BufferIsTrappedByMutator(buffer)) {
+    BufferFrameNotifyPopPending(buffer);
+  }
+
+  BufferDetach(buffer, pool);
+
+  /* Dispatch to the buffer class method to perform any  */
+  /* class-specific finishing of the buffer. */
+  (*buffer->class->finish)(buffer);
+
+  /* Detach the buffer from its owning pool and unsig it. */
+  RingRemove(&buffer->poolRing);
+  buffer->sig = SigInvalid;
+  
+  /* Finish off the generic buffer fields. */
+  RingFinish(&buffer->poolRing);
+
+  EVENT_P(BufferFinish, buffer);
+}
+
+
+/* BufferIsReset -- test whether a buffer is in the "reset" state
+ *
+ * A buffer is "reset" when it is not attached.  In this state all of
+ * the pointers into the region are zero.  This condition is checked by
+ * BufferCheck.  */
+
+Bool BufferIsReset(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+
+  return !(buffer->mode & BufferModeATTACHED);
+}
+
+
+/* BufferIsReady -- test whether a buffer is ready for reserve
+ *
+ * BufferIsReady returns TRUE if and only if the buffer is not between a
+ * reserve and commit.  The result is only reliable if the client is not
+ * currently using the buffer, since it may update the alloc and init
+ * pointers asynchronously.  */
+
+Bool BufferIsReady(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+
+  return buffer->apStruct.init == buffer->apStruct.alloc;
+}
+
+
+/* BufferIsMutator -- test whether buffer belongs to mutator
+ *
+ * Returns TRUE iff mutator was created for the mutator.  */
+
+Bool BufferIsMutator(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+
+  return buffer->isMutator;
+}
+
+
+/* BufferSetUnflipped
+ *
+ * Unflip a buffer if it was flipped.  */
+
+static void BufferSetUnflipped(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  AVER(buffer->mode & BufferModeFLIPPED);
+  buffer->mode &= ~BufferModeFLIPPED;
+  /* restore apStruct.limit if appropriate */
+  if (!BufferIsTrapped(buffer)) {
+    buffer->apStruct.limit = buffer->poolLimit;
+  }
+  buffer->initAtFlip = (Addr)0;
+}
+
+
+/* BufferFrameState
+ *
+ * Returns the frame state of a buffer.  See
+ * design.mps.alloc-frame.lw-frame.states.  */
+
+FrameState BufferFrameState(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  if (buffer->apStruct.enabled) {
+    if (buffer->apStruct.lwPopPending) {
+      return BufferFramePOP_PENDING;
+    } else {
+      AVER(buffer->apStruct.frameptr == NULL);
+      return BufferFrameVALID;
+    }
+  } else {
+    AVER(buffer->apStruct.frameptr == NULL);
+    AVER(buffer->apStruct.lwPopPending == FALSE);
+    return BufferFrameDISABLED;
+  }
+}
+
+
+/* BufferFrameSetState
+ *
+ * Sets the frame state of a buffer.  Only the mutator may set the
+ * PopPending state.  See design.mps.alloc-frame.lw-frame.states.  */
+
+void BufferFrameSetState(Buffer buffer, FrameState state)
+{
+  AVERT(Buffer, buffer);
+  AVER(state == BufferFrameVALID || state == BufferFrameDISABLED);
+  buffer->apStruct.frameptr = NULL;
+  buffer->apStruct.lwPopPending = FALSE;
+  buffer->apStruct.enabled = (state == BufferFrameVALID);
+}
+
+
+/* BufferSetAllocAddr
+ *
+ * Sets the init & alloc pointers of a buffer.  */
+
+void BufferSetAllocAddr(Buffer buffer, Addr addr)
+{
+  AVERT(Buffer, buffer);
+  /* Can't check Addr */
+  AVER(BufferIsReady(buffer));
+  AVER(buffer->base <= addr);
+  AVER(buffer->poolLimit >= addr);
+
+  buffer->apStruct.init = addr;
+  buffer->apStruct.alloc = addr;
+}
+
+
+/* BufferFrameNotifyPopPending
+ *
+ * Notifies the pool when a lightweight frame pop operation has been
+ * deferred and needs to be processed.  See
+ * design.mps.alloc-frame.lw-frame.sync.trip.  */
+
+static void BufferFrameNotifyPopPending(Buffer buffer)
+{
+  AllocFrame frame;
+  Pool pool;
+  AVER(BufferIsTrappedByMutator(buffer));
+  AVER(BufferFrameState(buffer) == BufferFramePOP_PENDING);
+  frame = (AllocFrame)buffer->apStruct.frameptr;
+  /* Unset PopPending state & notify the pool */
+  BufferFrameSetState(buffer, BufferFrameVALID);
+  /* If the frame is no longer trapped, undo the trap by resetting */
+  /* the AP limit pointer */
+  if (!BufferIsTrapped(buffer)) {
+    buffer->apStruct.limit = buffer->poolLimit;
+  }
+  pool = BufferPool(buffer);
+  (*pool->class->framePopPending)(pool, buffer, frame);
+}
+
+
+
+/* BufferFramePush
+ *
+ * See design.mps.alloc-frame.  */
+
+Res BufferFramePush(AllocFrame *frameReturn, Buffer buffer)
+{
+  Pool pool;
+  AVERT(Buffer, buffer);
+  AVER(frameReturn != NULL);
+
+
+  /* Process any flip or PopPending */
+  if (!BufferIsReset(buffer) && buffer->apStruct.limit == (Addr)0) {
+    /* .fill.unflip: If the buffer is flipped then we unflip the buffer. */
+    if (buffer->mode & BufferModeFLIPPED) {
+      BufferSetUnflipped(buffer);
+    }
+  
+    /* check for PopPending */
+    if (BufferIsTrappedByMutator(buffer)) {
+      BufferFrameNotifyPopPending(buffer);
+    }
+  }
+  pool = BufferPool(buffer);
+  return (*pool->class->framePush)(frameReturn, pool, buffer);
+}
+
+
+/* BufferFramePop
+ *
+ * See design.mps.alloc-frame.  */
+
+Res BufferFramePop(Buffer buffer, AllocFrame frame)
+{
+  Pool pool;
+  AVERT(Buffer, buffer);
+  /* frame is of an abstract type & can't be checked */
+  pool = BufferPool(buffer);
+  return (*pool->class->framePop)(pool, buffer, frame);
+  
+}
+
+
+
+/* BufferReserve -- reserve memory from an allocation buffer
+ *
+ * .reserve: Keep in sync with impl.h.mps.reserve.  */
+
+Res BufferReserve(Addr *pReturn, Buffer buffer, Size size,
+                  Bool withReservoirPermit)
+{
+  Addr next;
+
+  AVER(pReturn != NULL);
+  AVERT(Buffer, buffer);
+  AVER(size > 0);
+  AVER(SizeIsAligned(size, BufferPool(buffer)->alignment));
+  AVER(BufferIsReady(buffer));
+  AVER(BoolCheck(withReservoirPermit));
+
+  /* Is there enough room in the unallocated portion of the buffer to */
+  /* satisfy the request?  If so, just increase the alloc marker and */
+  /* return a pointer to the area below it. */
+  next = AddrAdd(buffer->apStruct.alloc, size);
+  if (next > buffer->apStruct.alloc && next <= buffer->apStruct.limit) {
+    buffer->apStruct.alloc = next;
+    *pReturn = buffer->apStruct.init;
+    return ResOK;
+  }
+
+  /* If the buffer can't accommodate the request, call "fill". */
+  return BufferFill(pReturn, buffer, size, withReservoirPermit);
+}
+
+
+/* BufferAttach -- attach a region to a buffer
+ *
+ * BufferAttach is entered because of a BufferFill, or because of a Pop
+ * operation on a lightweight frame.  */
+
+void BufferAttach(Buffer buffer, Addr base, Addr limit, 
+                  Addr init, Size size)
+{
+  Size filled;
+
+  AVERT(Buffer, buffer);
+  AVER(BufferIsReset(buffer));
+  AVER(AddrAdd(base, size) <= limit);
+  AVER(base <= init);
+  AVER(init <= limit);
+
+  /* Set up the buffer to point at the supplied region */
+  buffer->mode |= BufferModeATTACHED;
+  buffer->base = base;
+  buffer->apStruct.init = init;
+  buffer->apStruct.alloc = AddrAdd(init, size);
+  /* only set limit if not logged */
+  if ((buffer->mode & BufferModeLOGGED) == 0) {
+    buffer->apStruct.limit = limit;
+  } else {
+    AVER(buffer->apStruct.limit == (Addr)0);
+  }
+  AVER(buffer->initAtFlip == (Addr)0);
+  buffer->poolLimit = limit;
+
+  filled = AddrOffset(init, limit);
+  buffer->fillSize += filled;
+  if (buffer->isMutator) {
+    if (base != init) { /* see design.mps.buffer.count.alloc.how */
+      Size prealloc = AddrOffset(base, init);
+      ArenaGlobals(buffer->arena)->allocMutatorSize -= prealloc;
+    }
+    buffer->pool->fillMutatorSize += filled;
+    ArenaGlobals(buffer->arena)->fillMutatorSize += filled;
+  } else {
+    buffer->pool->fillInternalSize += filled;
+    ArenaGlobals(buffer->arena)->fillInternalSize += filled;
+  }
+
+  /* run any class-specific attachment method */
+  buffer->class->attach(buffer, base, limit, init, size);
+
+  AVERT(Buffer, buffer);
+  EVENT_PWAW(BufferFill, buffer, size, base, filled);
+}
+
+
+/* BufferFill -- refill an empty buffer
+ *
+ * BufferFill is entered by the "reserve" operation on a buffer if there
+ * isn't enough room between "alloc" and "limit" to satisfy an
+ * allocation request.  This might be because the buffer has been
+ * trapped and "limit" has been set to zero.  */
+
+Res BufferFill(Addr *pReturn, Buffer buffer, Size size,
+               Bool withReservoirPermit)
+{
+  Res res;
+  Pool pool;
+  Addr base, limit, next;
+
+  AVER(pReturn != NULL);
+  AVERT(Buffer, buffer);
+  AVER(size > 0);
+  AVER(SizeIsAligned(size, BufferPool(buffer)->alignment));
+  AVER(BufferIsReady(buffer));
+
+  pool = BufferPool(buffer);
+
+  /* If we're here because the buffer was trapped, then we attempt */
+  /* the allocation here. */
+  if (!BufferIsReset(buffer) && buffer->apStruct.limit == (Addr)0) {
+    /* .fill.unflip: If the buffer is flipped then we unflip the buffer. */
+    if (buffer->mode & BufferModeFLIPPED) {
+      BufferSetUnflipped(buffer);
+    }
+
+    /* design.mps.alloc-frame.lw-frame.sync.trip */
+    if (BufferIsTrappedByMutator(buffer)) {
+      BufferFrameNotifyPopPending(buffer);
+    }
+
+    /* .fill.logged: If the buffer is logged then we leave it logged. */
+    next = AddrAdd(buffer->apStruct.alloc, size);
+    if (next > buffer->apStruct.alloc &&
+       next <= buffer->poolLimit) {
+      buffer->apStruct.alloc = next;
+      if (buffer->mode & BufferModeLOGGED) {
+        EVENT_PAW(BufferReserve, buffer, buffer->apStruct.init, size);
+      }
+      *pReturn = buffer->apStruct.init;
+      return ResOK;
+    }
+  }
+
+  /* There really isn't enough room for the allocation now. */
+  AVER(AddrAdd(buffer->apStruct.alloc, size) > buffer->poolLimit
+       || AddrAdd(buffer->apStruct.alloc, size) < buffer->apStruct.alloc);
+
+  BufferDetach(buffer, pool);
+
+  /* Ask the pool for some memory. */
+  res = (*pool->class->bufferFill)(&base, &limit,
+                                   pool, buffer, size,
+                                   withReservoirPermit);
+  if (res != ResOK)
+    return res;
+
+  /* Set up the buffer to point at the memory given by the pool */
+  /* and do the allocation that was requested by the client. */
+  BufferAttach(buffer, base, limit, base, size);
+
+  if (buffer->mode & BufferModeLOGGED) {
+    EVENT_PAW(BufferReserve, buffer, buffer->apStruct.init, size);
+  }
+
+  *pReturn = base;
+  return res;
+}
+
+
+
+/* BufferCommit -- commit memory previously reserved
+ *
+ * .commit: Keep in sync with impl.h.mps.commit.  */
+
+Bool BufferCommit(Buffer buffer, Addr p, Size size)
+{
+  AVERT(Buffer, buffer);
+  AVER(size > 0);
+  AVER(SizeIsAligned(size, BufferPool(buffer)->alignment));
+  AVER(!BufferIsReady(buffer));
+
+  /* See design.mps.collection.flip. */
+  /* .commit.before: If a flip occurs before this point, when the */
+  /* pool reads "initAtFlip" it will point below the object, so it */
+  /* will be trashed and the commit must fail when trip is called.  */
+  AVER(p == buffer->apStruct.init);
+  AVER(AddrAdd(buffer->apStruct.init, size) == buffer->apStruct.alloc);
+
+  /* .commit.update: Atomically update the init pointer to declare */
+  /* that the object is initialized (though it may be invalid if a */
+  /* flip occurred). */
+  buffer->apStruct.init = buffer->apStruct.alloc;
+
+  /* .improve.memory-barrier: Memory barrier here on the DEC Alpha */
+  /* (and other relaxed memory order architectures). */
+  /* .commit.after: If a flip occurs at this point, the pool will */
+  /* see "initAtFlip" above the object, which is valid, so it will */
+  /* be collected.  The commit must succeed when trip is called.  */
+  /* The pointer "p" will have been fixed up.  (@@@@ Will it?) */
+  /* .commit.trip: Trip the buffer if a flip has occurred. */
+  if (buffer->apStruct.limit == 0)
+    return BufferTrip(buffer, p, size);
+
+  /* No flip occurred, so succeed. */
+
+  return TRUE;
+}
+
+
+/* BufferTrip -- act on a trapped buffer
+ *
+ * Called from BufferCommit (and its equivalents) when invoked on a
+ * trapped buffer (indicated by limit == 0).  This function can decide
+ * whether to succeed or fail the commit.  */
+
+Bool BufferTrip(Buffer buffer, Addr p, Size size)
+{
+  Pool pool;
+
+  AVERT(Buffer, buffer);
+  AVER(p != 0);
+  AVER(size > 0);
+  AVER(SizeIsAligned(size, buffer->alignment));
+
+  /* The limit field should be zero, because that's how trip gets */
+  /* called.  See .commit.trip. */
+  AVER(buffer->apStruct.limit == 0);
+  /* Of course we should be trapped. */
+  AVER(BufferIsTrapped(buffer));
+  /* But the mutator shouldn't have caused the trap */
+  AVER(!BufferIsTrappedByMutator(buffer));
+
+  /* The init and alloc fields should be equal at this point, because */
+  /* the step .commit.update has happened. */
+  AVER(buffer->apStruct.init == buffer->apStruct.alloc);
+
+  /* The p parameter points at the base address of the allocated */
+  /* block, the end of which should now coincide with the init and */
+  /* alloc fields. */
+  /* Note that we don't _really_ care about p too much.  We don't */
+  /* do anything else with it apart from these checks. (in particular */
+  /* it seems like the algorithms could be modified to cope with the */
+  /* case of the object having been copied between Commit updating i */
+  /* and testing limit) */
+  AVER(AddrAdd(p, size) == buffer->apStruct.init);
+
+  pool = BufferPool(buffer);
+
+  AVER(PoolHasAddr(pool, p));
+
+  /* .trip.unflip: If the flip occurred before commit set "init" */
+  /* to "alloc" (see .commit.before) then the object is invalid */
+  /* (won't've been scanned) so undo the allocation and fail commit. */
+  /* Otherwise (see .commit.after) the object is valid (will've been */
+  /* scanned) so commit can simply succeed. */
+  if ((buffer->mode & BufferModeFLIPPED)
+      && buffer->apStruct.init != buffer->initAtFlip) {
+    /* Reset just enough state for Reserve/Fill to work. */
+    /* The buffer is left trapped and we leave the untrapping */
+    /* for the next reserve (which goes out of line to Fill */
+    /* (.fill.unflip) because the buffer is still trapped) */
+    buffer->apStruct.init = p;
+    buffer->apStruct.alloc = p;
+    return FALSE;
+  }
+
+  /* Emit event including class if loggged */
+  if (buffer->mode & BufferModeLOGGED) {
+    Bool b;
+    Format format;
+    Addr clientClass;
+
+    b = PoolFormat(&format, buffer->pool);
+    if (b) {
+      clientClass = format->class(p);
+    } else {
+      clientClass = (Addr)0;
+    }
+    EVENT_PAWA(BufferCommit, buffer, p, size, clientClass);
+    /* Of course, it's not _really_ unused unless you're not */
+    /* using telemetry.  This is a HACK @@@@.  It should be */
+    /* removed when telemetry is fixed to use its arguments. */
+    UNUSED(clientClass);
+  }
+  return TRUE;
+}
+
+
+/* BufferFlip -- trap buffer at GC flip time
+ *
+ * .flip: Tells the buffer that a flip has occurred.  If the buffer is
+ * between reserve and commit, and has a rank (i.e. references), and has
+ * the two-phase protocol, then the object being initialized is
+ * invalidated by failing the next commit.  The buffer code handles this
+ * automatically (ie the pool implementation is not involved).  If the
+ * buffer is reset there is no effect, since there is no object to
+ * invalidate.  If the buffer is already flipped there is no effect,
+ * since the object is already invalid by a previous trace.  The buffer
+ * becomes unflipped at the next reserve or commit operation (actually
+ * reserve because commit is lazy).  This is handled by BufferFill
+ * (.fill.unflip) or BufferTrip (.trip.unflip).  */
+
+void BufferFlip(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+
+  if (BufferRankSet(buffer) != RankSetEMPTY
+      && (buffer->mode & BufferModeFLIPPED) == 0
+      && !BufferIsReset(buffer)) {
+    AVER(buffer->initAtFlip == (Addr)0);
+    buffer->initAtFlip = buffer->apStruct.init;
+    /* Memory Barrier here? @@@@ */
+    buffer->apStruct.limit = (Addr)0;
+    buffer->mode |= BufferModeFLIPPED;
+  }
+}
+
+
+/* BufferScanLimit -- return limit of data to which to scan
+ *
+ * Returns the highest address to which it is safe to scan objects in
+ * the buffer.  When the buffer is not flipped, this is the "init" of
+ * the AP.  When the buffer is flipped, it is the value that "init" had
+ * at flip time.  [Could make BufferScanLimit return the AP "alloc" when
+ * using ambiguous scanning.]  See .ap.async.  */
+
+Addr BufferScanLimit(Buffer buffer)
+{
+  if (buffer->mode & BufferModeFLIPPED) {
+    return buffer->initAtFlip;
+  } else {
+    return buffer->apStruct.init;
+  }
+}
+
+
+Seg BufferSeg(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  return buffer->class->seg(buffer);
+}
+
+
+RankSet BufferRankSet(Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  return buffer->class->rankSet(buffer);
+}
+
+void BufferSetRankSet(Buffer buffer, RankSet rankset)
+{
+  AVERT(Buffer, buffer);
+  AVERT(RankSet, rankset);
+  buffer->class->setRankSet(buffer, rankset);
+}
+
+
+/* BufferReassignSeg -- adjust the seg of an attached buffer
+ *
+ * Used for segment splitting and merging.  */
+
+void BufferReassignSeg(Buffer buffer, Seg seg)
+{
+  AVERT(Buffer, buffer);
+  AVERT(Seg, seg);
+  AVER(!BufferIsReset(buffer));
+  AVER(BufferBase(buffer) >= SegBase(seg));
+  AVER(BufferLimit(buffer) <= SegLimit(seg));
+  AVER(BufferPool(buffer) == SegPool(seg));
+  buffer->class->reassignSeg(buffer, seg);
+}
+
+
+/* BufferIsTrapped
+ *
+ * Indicates whether the buffer is trapped - either by MPS or the
+ * mutator.  See .ap.async.  */
+
+Bool BufferIsTrapped(Buffer buffer)
+{
+  /* Can't check buffer, see .check.use-trapped */
+  return BufferIsTrappedByMutator(buffer)
+         || ((buffer->mode & (BufferModeFLIPPED|BufferModeLOGGED)) != 0);
+}
+
+
+/* BufferIsTrappedByMutator
+ *
+ * Indicates whether the mutator trapped the buffer.  See
+ * design.mps.alloc-frame.lw-frame.sync.trip and .ap.async.  */
+
+Bool BufferIsTrappedByMutator(Buffer buffer)
+{
+  AVER(!buffer->apStruct.lwPopPending || buffer->apStruct.enabled);
+  /* Can't check buffer, see .check.use-trapped */
+  return buffer->apStruct.lwPopPending;
+}
+
+
+/* Alloc pattern functions
+ *
+ * Just represent the two patterns by two different pointers to dummies.  */
+
+AllocPatternStruct AllocPatternRampStruct = {'\0'};
+
+AllocPattern AllocPatternRamp(void)
+{
+  return &AllocPatternRampStruct;
+}
+
+AllocPatternStruct AllocPatternRampCollectAllStruct = {'\0'};
+
+AllocPattern AllocPatternRampCollectAll(void)
+{
+  return &AllocPatternRampCollectAllStruct;
+}
+
+static Bool AllocPatternCheck(AllocPattern pattern)
+{
+  CHECKL(pattern == &AllocPatternRampCollectAllStruct
+         || pattern == &AllocPatternRampStruct);
+  UNUSED(pattern); /* impl.c.mpm.check.unused */
+  return TRUE;
+}
+
+
+/* BufferRampBegin -- note an entry into a ramp pattern
+ *
+ * .ramp.hack: We count the number of times the ap has begun ramp mode
+ * (and not ended), so we can do reset by ending all the current ramps.  */
+
+void BufferRampBegin(Buffer buffer, AllocPattern pattern)
+{
+  Pool pool;
+
+  AVERT(Buffer, buffer);
+  AVERT(AllocPattern, pattern);
+
+  ++buffer->rampCount;
+  AVER(buffer->rampCount > 0);
+
+  pool = BufferPool(buffer);
+  AVERT(Pool, pool);
+  (*pool->class->rampBegin)(pool, buffer,
+                            pattern == &AllocPatternRampCollectAllStruct);
+}
+
+
+/* BufferRampEnd -- note an exit from a ramp pattern */
+
+Res BufferRampEnd(Buffer buffer)
+{
+  Pool pool;
+
+  AVERT(Buffer, buffer);
+
+  if (buffer->rampCount == 0)
+    return ResFAIL;
+  --buffer->rampCount;
+
+  pool = BufferPool(buffer);
+  AVERT(Pool, pool);
+  (*pool->class->rampEnd)(pool, buffer);
+  return ResOK;
+}
+
+
+/* BufferRampReset -- exit from ramp mode */
+
+void BufferRampReset(Buffer buffer)
+{
+  Pool pool;
+
+  AVERT(Buffer, buffer);
+
+  if (buffer->rampCount == 0)
+    return;
+
+  pool = BufferPool(buffer);
+  AVERT(Pool, pool);
+  do
+    (*pool->class->rampEnd)(pool, buffer);
+  while(--buffer->rampCount > 0);
+}
+
+
+
+/* BufferClass -- support for the basic Buffer class */
+
+
+/* bufferTrivInit -- basic buffer init method */
+
+static Res bufferTrivInit (Buffer buffer, Pool pool, va_list args)
+{
+  /* initialization happens in BufferInitV so checks are safe */
+  AVERT(Buffer, buffer);
+  AVERT(Pool, pool);
+  UNUSED(args);
+  EVENT_PPU(BufferInit, buffer, pool, buffer->isMutator);
+  return ResOK;
+}
+
+
+/* bufferTrivFinish -- basic buffer finish method */
+
+static void bufferTrivFinish (Buffer buffer)
+{
+  /* No special finish for simple buffers */
+  AVERT(Buffer, buffer);
+  AVER(BufferIsReset(buffer));
+  NOOP;
+}
+
+
+/* bufferTrivAttach -- basic buffer attach method */
+
+static void bufferTrivAttach(Buffer buffer, Addr base, Addr limit, 
+                             Addr init, Size size)
+{
+  /* No special attach method for simple buffers */
+  AVERT(Buffer, buffer);
+  /* Other parameters are consistency checked in BufferAttach */
+  UNUSED(base);
+  UNUSED(limit);
+  UNUSED(init);
+  UNUSED(size);
+  NOOP;
+}
+
+
+/* bufferTrivDetach -- basic buffer detach method */
+
+static void bufferTrivDetach(Buffer buffer)
+{
+  /* No special detach method for simple buffers */
+  AVERT(Buffer, buffer);
+  NOOP;
+}
+
+
+/* bufferNoSeg -- basic buffer BufferSeg accessor method 
+ *
+ * .noseg: basic buffers don't support segments, so this method should
+ * not be called.  */
+
+static Seg bufferNoSeg (Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  NOTREACHED;  /* .noseg */
+  return NULL;
+}
+
+
+
+/* bufferTrivRankSet -- basic BufferRankSet accessor method */
+
+static RankSet bufferTrivRankSet (Buffer buffer)
+{
+  AVERT(Buffer, buffer);
+  /* vanilla buffers can only have empty rank set */
+  return RankSetEMPTY;
+}
+
+
+/* bufferNoSetRankSet -- basic BufferSetRankSet setter method 
+ *
+ * .norank: basic buffers don't support ranksets, so this method should
+ * not be called.  */
+
+static void bufferNoSetRankSet (Buffer buffer, RankSet rankset)
+{
+  AVERT(Buffer, buffer);
+  AVERT(RankSet, rankset);
+  NOTREACHED; /* .norank */
+}
+
+
+/* bufferNoReassignSeg -- basic BufferReassignSeg method 
+ *
+ * .noseg: basic buffers don't support attachment to sements, so this
+ * method should not be called.  */
+
+static void bufferNoReassignSeg (Buffer buffer, Seg seg)
+{
+  AVERT(Buffer, buffer);
+  AVERT(Seg, seg);
+  NOTREACHED; /* .noseg */
+}
+
+
+/* bufferTrivDescribe -- basic Buffer describe method */
+
+static Res bufferTrivDescribe(Buffer buffer, mps_lib_FILE *stream)
+{
+  if (!CHECKT(Buffer, buffer)) return ResFAIL;
+  if (stream == NULL) return ResFAIL;
+  /* dispatching function does it all */
+  return ResOK;
+}
+
+
+/* BufferClassCheck -- check the consistency of a BufferClass */
+
+Bool BufferClassCheck(BufferClass class)
+{
+  CHECKL(ProtocolClassCheck(&class->protocol));
+  CHECKL(class->name != NULL); /* Should be <=6 char C identifier */
+  CHECKL(class->size >= sizeof(BufferStruct));
+  CHECKL(FUNCHECK(class->init));
+  CHECKL(FUNCHECK(class->finish));
+  CHECKL(FUNCHECK(class->attach));
+  CHECKL(FUNCHECK(class->detach));
+  CHECKL(FUNCHECK(class->seg));
+  CHECKL(FUNCHECK(class->rankSet));
+  CHECKL(FUNCHECK(class->setRankSet));
+  CHECKL(FUNCHECK(class->reassignSeg));
+  CHECKL(FUNCHECK(class->describe));
+  CHECKS(BufferClass, class);
+  return TRUE;
+} 
+
+
+/* BufferClass -- the vanilla buffer class definition 
+ *
+ * See design.mps.buffer.class.hierarchy.buffer.  */
+
+DEFINE_CLASS(BufferClass, class)
+{
+  INHERIT_CLASS(&class->protocol, ProtocolClass);
+  class->name = "BUFFER";
+  class->size = sizeof(BufferStruct);
+  class->init = bufferTrivInit;
+  class->finish = bufferTrivFinish;
+  class->attach = bufferTrivAttach;
+  class->detach = bufferTrivDetach;
+  class->describe = bufferTrivDescribe;
+  class->seg = bufferNoSeg;
+  class->rankSet = bufferTrivRankSet;
+  class->setRankSet = bufferNoSetRankSet;
+  class->reassignSeg = bufferNoReassignSeg;
+  class->sig = BufferClassSig;
+}
+
+
+
+/* SegBufClass -- support for the SegBuf subclass */
+
+
+/* BufferSegBuf -- convert generic Buffer to a SegBuf */
+
+#define BufferSegBuf(buffer) ((SegBuf)(buffer))
+
+
+/* SegBufCheck -- check consistency of a SegBuf */
+
+Bool SegBufCheck(SegBuf segbuf)
+{
+  Buffer buffer;
+
+  CHECKS(SegBuf, segbuf);
+  buffer = &segbuf->bufferStruct;
+  CHECKL(BufferCheck(buffer));
+  CHECKL(RankSetCheck(segbuf->rankSet));
+
+  if (buffer->mode & BufferModeTRANSITION) {
+    /* nothing to check */
+  } else if ((buffer->mode & BufferModeATTACHED) == 0) {
+    CHECKL(segbuf->seg == NULL);
+  } else {
+    /* The buffer is attached to a segment. */
+    CHECKL(segbuf->seg != NULL);
+    CHECKL(SegCheck(segbuf->seg));
+    /* To avoid recursive checking, leave it to SegCheck to make */
+    /* sure the buffer and segment fields tally. */
+    
+    if (buffer->mode & BufferModeFLIPPED) {
+      /* Only buffers that allocate pointers get flipped. */
+      CHECKL(segbuf->rankSet != RankSetEMPTY);
+    }
+  }
+
+  return TRUE;
+}
+
+
+/* segBufInit -- SegBuf init method */
+
+static Res segBufInit (Buffer buffer, Pool pool, va_list args)
+{
+  BufferClass super;
+  SegBuf segbuf;
+  Res res;
+
+  AVERT(Buffer, buffer);
+  AVERT(Pool, pool);
+  segbuf = BufferSegBuf(buffer);
+
+  /* Initialize the superclass fields first via next-method call */
+  super = BUFFER_SUPERCLASS(SegBufClass);
+  res = super->init(buffer, pool, args);
+  if (res != ResOK)
+    return res;
+
+  segbuf->seg = NULL;
+  segbuf->sig = SegBufSig;
+  segbuf->rankSet = RankSetEMPTY;
+
+  AVERT(SegBuf, segbuf);
+  EVENT_PPU(BufferInitSeg, buffer, pool, buffer->isMutator);
+  return ResOK;
+}
+
+
+/* segBufFinish -- SegBuf finish method */
+
+static void segBufFinish (Buffer buffer)
+{
+  BufferClass super;
+  SegBuf segbuf;
+
+  AVERT(Buffer, buffer);
+  AVER(BufferIsReset(buffer));
+  segbuf = BufferSegBuf(buffer);
+  AVERT(SegBuf, segbuf);
+
+  segbuf->sig = SigInvalid;
+
+  /* finish the superclass fields last */
+  super = BUFFER_SUPERCLASS(SegBufClass);
+  super->finish(buffer);
+}
+
+
+/* segBufAttach -- SegBuf attach method */
+
+static void segBufAttach(Buffer buffer, Addr base, Addr limit, 
+                         Addr init, Size size)
+{
+  SegBuf segbuf;
+  Seg seg;
+  Arena arena;
+  Bool found;
+
+  AVERT(Buffer, buffer);
+  /* Other parameters are consistency checked in BufferAttach */
+  UNUSED(init);
+  UNUSED(size);
+
+  segbuf = BufferSegBuf(buffer);
+  arena = BufferArena(buffer);
+  found = SegOfAddr(&seg, arena, base);
+  AVER(found);
+  AVER(segbuf->seg == NULL);
+  AVER(SegBuffer(seg) == NULL);
+  AVER(SegBase(seg) <= base);
+  AVER(limit <= SegLimit(seg));
+
+  /* attach the buffer to the segment */
+  SegSetBuffer(seg, buffer);
+  segbuf->seg = seg;
+
+  AVERT(SegBuf, segbuf);
+}
+
+
+/* segBufDetach -- SegBuf detach method */
+
+static void segBufDetach(Buffer buffer)
+{
+  SegBuf segbuf;
+  Seg seg;
+
+  AVERT(Buffer, buffer);
+  segbuf = BufferSegBuf(buffer);
+  AVERT(SegBuf, segbuf);
+
+  seg = segbuf->seg;
+  AVER(seg != NULL);
+  SegSetBuffer(seg, NULL);
+  segbuf->seg = NULL;
+}
+
+
+/* segBufSeg -- BufferSeg accessor method for SegBuf instances */
+
+static Seg segBufSeg (Buffer buffer)
+{
+  SegBuf segbuf;
+
+  AVERT(Buffer, buffer);
+  segbuf = BufferSegBuf(buffer);
+  AVERT(SegBuf, segbuf);
+  return segbuf->seg;
+}
+
+
+/* segBufRankSet -- BufferRankSet accessor for SegBuf instances */
+
+static RankSet segBufRankSet (Buffer buffer)
+{
+  SegBuf segbuf;
+
+  AVERT(Buffer, buffer);
+  segbuf = BufferSegBuf(buffer);
+  AVERT(SegBuf, segbuf);
+  return segbuf->rankSet;
+}
+
+
+/* segBufSetRankSet -- BufferSetRankSet setter method for SegBuf */
+
+static void segBufSetRankSet (Buffer buffer, RankSet rankset)
+{
+  SegBuf segbuf;
+
+  AVERT(Buffer, buffer);
+  AVERT(RankSet, rankset);
+  segbuf = BufferSegBuf(buffer);
+  AVERT(SegBuf, segbuf);
+  segbuf->rankSet = rankset;
+}
+
+
+/* segBufReassignSeg -- BufferReassignSeg method for SegBuf
+ *
+ * Used to support segment merging and splitting.
+ *
+ * .invseg: On entry the buffer is attached to an invalid segment, which
+ * can't be checked. The method is called to make the attachment valid.  */
+
+static void segBufReassignSeg (Buffer buffer, Seg seg)
+{
+  SegBuf segbuf;
+
+  AVERT(Buffer, buffer);
+  AVERT(Seg, seg);
+  segbuf = BufferSegBuf(buffer);
+  /* Can't check segbuf on entry. See .invseg */
+  AVER(NULL != segbuf->seg);
+  AVER(seg != segbuf->seg);
+  segbuf->seg = seg;
+  AVERT(SegBuf, segbuf);
+}
+
+
+/* segBufDescribe --  describe method for SegBuf */
+
+static Res segBufDescribe(Buffer buffer, mps_lib_FILE *stream)
+{
+  SegBuf segbuf;
+  BufferClass super;
+  Res res;
+
+  if (!CHECKT(Buffer, buffer)) return ResFAIL;
+  if (stream == NULL) return ResFAIL;
+  segbuf = BufferSegBuf(buffer);
+  if (!CHECKT(SegBuf, segbuf)) return ResFAIL;
+
+  /* Describe the superclass fields first via next-method call */
+  super = BUFFER_SUPERCLASS(SegBufClass);
+  res = super->describe(buffer, stream);
+  if (res != ResOK) return res;
+
+  res = WriteF(stream,
+               "  Seg $P\n",         (WriteFP)segbuf->seg,
+               "  rankSet $U\n",     (WriteFU)segbuf->rankSet,
+               NULL);
+
+  return res;
+}
+
+
+/* SegBufClass -- SegBuf class definition 
+ *
+ * Supports an association with a single segment when attached.  See
+ * design.mps.buffer.class.hierarchy.segbuf.  */
+ 
+typedef BufferClassStruct SegBufClassStruct;
+
+DEFINE_CLASS(SegBufClass, class)
+{
+  INHERIT_CLASS(class, BufferClass);
+  class->name = "SEGBUF";
+  class->size = sizeof(SegBufStruct);
+  class->init = segBufInit;
+  class->finish = segBufFinish;
+  class->attach = segBufAttach;
+  class->detach = segBufDetach;
+  class->describe = segBufDescribe;
+  class->seg = segBufSeg;
+  class->rankSet = segBufRankSet;
+  class->setRankSet = segBufSetRankSet;
+  class->reassignSeg = segBufReassignSeg;
+}
+
+
+/* RankBufClass -- support for the RankBufClass subclass */
+
+
+/* rankBufInit -- RankBufClass init method */
+
+static Res rankBufInit (Buffer buffer, Pool pool, va_list args)
+{
+  /* Assumes pun compatibility between Rank and mps_rank_t */
+  /* Which is checked by mpsi_check in impl.c.mpsi */
+  Rank rank = va_arg(args, Rank);
+  BufferClass super;
+  Res res;
+
+  AVERT(Buffer, buffer);
+  AVERT(Pool, pool);
+  AVER(RankCheck(rank));
+
+  /* Initialize the superclass fields first via next-method call */
+  super = BUFFER_SUPERCLASS(RankBufClass);
+  res = super->init(buffer, pool, args);
+  if (res != ResOK)
+    return res;
+
+  BufferSetRankSet(buffer, RankSetSingle(rank));
+
+  /* There's nothing to check that the superclass doesn't, so no AVERT. */
+  EVENT_PPUU(BufferInitRank, buffer, pool, buffer->isMutator, rank);
+  return ResOK;
+}
+
+
+/* RankBufClass -- RankBufClass class definition 
+ *
+ * A subclass of SegBufClass, sharing structure for instances.
+ *
+ * Supports initialization to a rank supplied at creation time.  */
+ 
+typedef BufferClassStruct RankBufClassStruct;
+
+DEFINE_CLASS(RankBufClass, class)
+{
+  INHERIT_CLASS(class, SegBufClass);
+  class->name = "RANKBUF";
+  class->init = rankBufInit;
+}