implement 'dump_modify maxfiles' feature as discussed

doc/src/dump_modify.txt

@@ -15,7 +15,7 @@ dump_modify dump-ID keyword values ... :pre
 dump-ID = ID of dump to modify :ulb,l
 one or more keyword/value pairs may be appended :l
 these keywords apply to various dump styles :l
-keyword = {append} or {at} or {buffer} or {delay} or {element} or {every} or {fileper} or {first} or {flush} or {format} or {image} or {label} or {nfile} or {pad} or {precision} or {region} or {scale} or {sort} or {thresh} or {unwrap} :l
+keyword = {append} or {at} or {buffer} or {delay} or {element} or {every} or {fileper} or {first} or {flush} or {format} or {image} or {label} or {maxfiles} or {nfile} or {pad} or {precision} or {region} or {scale} or {sort} or {thresh} or {unwrap} :l
   {append} arg = {yes} or {no}
   {at} arg = N
     N = index of frame written upon first dump
@@ -37,6 +37,8 @@ keyword = {append} or {at} or {buffer} or {delay} or {element} or {every} or {fi
   {image} arg = {yes} or {no}
   {label} arg = string
     string = character string (e.g. BONDS) to use in header of dump local file
+  {maxfiles} arg = maxf
+    maxf = retain at most {maxf} files when writing one file per timestepq
   {nfile} arg = Nf
     Nf = write this many files, one from each of Nf processors
   {pad} arg = Nchar = # of characters to convert timestep to
@@ -364,6 +366,15 @@ e.g. BONDS or ANGLES.
 
 :line
 
+The {maxfiles} keyword applies only to dumps with a '*' wildcard included
+in the dump file name, i.e. when writing one file per frame. The number
+following the keyword determines the maximum number of files being written.
+If this number is reached, the olders dump file from the current sequence
+is deleted before a new dump file is written. A {maxfiles} value of -1
+or 0 indicates that all files are retained.
+
+:line
+
 The {nfile} or {fileper} keywords can be used in conjunction with the
 "%" wildcard character in the specified dump file name, for all dump
 styles except the {dcd}, {image}, {movie}, {xtc}, and {xyz} styles
@@ -901,6 +912,7 @@ flush = yes
 format = %d and %g for each integer or floating point value
 image = no
 label = ENTRIES
+maxifiles = -1
 nfile = 1
 pad = 0
 pbc = no

src/dump.cpp

@@ -91,6 +91,11 @@ Dump::Dump(LAMMPS *lmp, int narg, char **arg) : Pointers(lmp)
   pbcflag = 0;
   delay_flag = 0;
 
+  maxfiles = -1;
+  numfiles = 0;
+  fileidx = 0;
+  nameslist = NULL;
+
   maxbuf = maxids = maxsort = maxproc = 0;
   buf = bufsort = NULL;
   ids = idsort = NULL;
@@ -187,6 +192,13 @@ Dump::~Dump()
 
   if (multiproc) MPI_Comm_free(&clustercomm);
 
+  // delete storage for caching file names
+  if (maxfiles > 0) {
+    for (int idx=0; idx < numfiles; ++idx)
+      delete[] nameslist[idx];
+    delete[] nameslist;
+  }
+
   // XTC style sets fp to NULL since it closes file in its destructor
 
   if (multifile == 0 && fp != NULL) {
@@ -549,6 +561,19 @@ void Dump::openfile()
       sprintf(filecurrent,pad,filestar,update->ntimestep,ptr+1);
     }
     *ptr = '*';
+    if (maxfiles > 0) {
+      if (numfiles < maxfiles) {
+        nameslist[numfiles] = new char[strlen(filecurrent)+1];
+        strcpy(nameslist[numfiles],filecurrent);
+        ++numfiles;
+      } else {
+        remove(nameslist[fileidx]);
+        delete[] nameslist[fileidx];
+        nameslist[fileidx] = new char[strlen(filecurrent)+1];
+        strcpy(nameslist[fileidx],filecurrent);
+        fileidx = (fileidx + 1) % maxfiles;
+      }
+    } 
   }
 
   // each proc with filewriter = 1 opens a file
@@ -1003,6 +1028,27 @@ void Dump::modify_params(int narg, char **arg)
         iarg += n;
       }
 
+    } else if (strcmp(arg[iarg],"maxfiles") == 0) {
+      if (iarg+2 > narg) error->all(FLERR,"Illegal dump_modify command");
+      if (!multifile)
+        error->all(FLERR,"Cannot use dump_modify maxfiles "
+                   "without * in dump file name");
+      // wipe out existing storage
+      if (maxfiles > 0) {
+        for (int idx=0; idx < numfiles; ++idx)
+          delete[] nameslist[idx];
+        delete[] nameslist;
+      }
+      maxfiles = force->inumeric(FLERR,arg[iarg+1]);
+      if (maxfiles == 0) error->all(FLERR,"Illegal dump_modify command");
+      if (maxfiles > 0) {
+        nameslist = new char*[maxfiles];
+        numfiles = 0;
+        for (int idx=0; idx < maxfiles; ++idx)
+          nameslist[idx] = NULL;
+        fileidx = 0;
+      }
+      iarg += 2;
     } else if (strcmp(arg[iarg],"nfile") == 0) {
       if (iarg+2 > narg) error->all(FLERR,"Illegal dump_modify command");
       if (!multiproc)

src/dump.h

@@ -105,6 +105,11 @@ class Dump : protected Pointers {
   double boxzlo,boxzhi;
   double boxxy,boxxz,boxyz;
 
+  int maxfiles;              // max number of files created, -1 == infinite
+  int numfiles;              // number of files in names list
+  int fileidx;               // index of file in names list
+  char **nameslist;          // list of history file names
+
   bigint ntotal;             // total # of per-atom lines in snapshot
   int reorderflag;           // 1 if OK to reorder instead of sort
   int ntotal_reorder;        // # of atoms that must be in snapshot