[PATCH 3/3] gdb: use intrusive_list for linux-nat lwp_list

[Simon Marchi <simon.marchi@polymtl.ca>]

Replace the manually maintained linked list of lwp_info objects with
intrusive_list.  Replace the ALL_LWPS macro with all_lwps, which returns
a range.  Add all_lwps_safe as well, for use in iterate_over_lwps, which
currently iterates in a safe manner.

Change-Id: I355313502510acc0103f5eaf2fbde80897d6376c
---
 gdb/ia64-linux-nat.c  |  8 +++-----
 gdb/linux-nat.c       | 46 ++++++++++++++++++++++---------------------
 gdb/linux-nat.h       | 35 +++++++++++++++-----------------
 gdb/linux-thread-db.c |  3 +--
 gdb/mips-linux-nat.c  |  7 ++-----
 5 files changed, 46 insertions(+), 53 deletions(-)

diff --git a/gdb/ia64-linux-nat.c b/gdb/ia64-linux-nat.c
index 6381e5318e68..371d51f00bba 100644
--- a/gdb/ia64-linux-nat.c
+++ b/gdb/ia64-linux-nat.c
@@ -589,7 +589,6 @@ ia64_linux_nat_target::insert_watchpoint (CORE_ADDR addr, int len,
 					  enum target_hw_bp_type type,
 					  struct expression *cond)
 {
-  struct lwp_info *lp;
   int idx;
   long dbr_addr, dbr_mask;
   int max_watchpoints = 4;
@@ -630,7 +629,8 @@ ia64_linux_nat_target::insert_watchpoint (CORE_ADDR addr, int len,
 
   debug_registers[2 * idx] = dbr_addr;
   debug_registers[2 * idx + 1] = dbr_mask;
-  ALL_LWPS (lp)
+
+  for (const lwp_info *lp : all_lwps ())
     {
       store_debug_register_pair (lp->ptid, idx, &dbr_addr, &dbr_mask);
       enable_watchpoints_in_psr (lp->ptid);
@@ -657,14 +657,12 @@ ia64_linux_nat_target::remove_watchpoint (CORE_ADDR addr, int len,
       dbr_mask = debug_registers[2 * idx + 1];
       if ((dbr_mask & (0x3UL << 62)) && addr == (CORE_ADDR) dbr_addr)
 	{
-	  struct lwp_info *lp;
-
 	  debug_registers[2 * idx] = 0;
 	  debug_registers[2 * idx + 1] = 0;
 	  dbr_addr = 0;
 	  dbr_mask = 0;
 
-	  ALL_LWPS (lp)
+	  for (const lwp_info *lp : all_lwps ())
 	    store_debug_register_pair (lp->ptid, idx, &dbr_addr, &dbr_mask);
 
 	  return 0;
diff --git a/gdb/linux-nat.c b/gdb/linux-nat.c
index 930209db6e89..fd01bd9301c0 100644
--- a/gdb/linux-nat.c
+++ b/gdb/linux-nat.c
@@ -421,9 +421,8 @@ static int
 num_lwps (int pid)
 {
   int count = 0;
-  struct lwp_info *lp;
 
-  for (lp = lwp_list; lp; lp = lp->next)
+  for (const lwp_info *lp ATTRIBUTE_UNUSED : all_lwps ())
     if (lp->ptid.pid () == pid)
       count++;
 
@@ -700,17 +699,31 @@ lwp_lwpid_htab_add_lwp (struct lwp_info *lp)
    creation order.  This order is assumed in some cases.  E.g.,
    reaping status after killing alls lwps of a process: the leader LWP
    must be reaped last.  */
-struct lwp_info *lwp_list;
+
+static intrusive_list<lwp_info> lwp_list;
+
+/* See linux-nat.h.  */
+
+lwp_info_range
+all_lwps ()
+{
+  return lwp_info_range (lwp_list.begin ());
+}
+
+/* See linux-nat.h.  */
+
+lwp_info_safe_range
+all_lwps_safe ()
+{
+  return lwp_info_safe_range (lwp_list.begin ());
+}
 
 /* Add LP to sorted-by-reverse-creation-order doubly-linked list.  */
 
 static void
 lwp_list_add (struct lwp_info *lp)
 {
-  lp->next = lwp_list;
-  if (lwp_list != NULL)
-    lwp_list->prev = lp;
-  lwp_list = lp;
+  lwp_list.push_front (*lp);
 }
 
 /* Remove LP from sorted-by-reverse-creation-order doubly-linked
@@ -720,12 +733,7 @@ static void
 lwp_list_remove (struct lwp_info *lp)
 {
   /* Remove from sorted-by-creation-order list.  */
-  if (lp->next != NULL)
-    lp->next->prev = lp->prev;
-  if (lp->prev != NULL)
-    lp->prev->next = lp->next;
-  if (lp == lwp_list)
-    lwp_list = lp->next;
+  lwp_list.erase (lwp_list.iterator_to (*lp));
 }
 
 \f
@@ -922,12 +930,8 @@ struct lwp_info *
 iterate_over_lwps (ptid_t filter,
 		   gdb::function_view<iterate_over_lwps_ftype> callback)
 {
-  struct lwp_info *lp, *lpnext;
-
-  for (lp = lwp_list; lp; lp = lpnext)
+  for (lwp_info *lp : all_lwps_safe ())
     {
-      lpnext = lp->next;
-
       if (lp->ptid.matches (filter))
 	{
 	  if (callback (lp) != 0)
@@ -3716,8 +3720,6 @@ linux_nat_target::thread_alive (ptid_t ptid)
 void
 linux_nat_target::update_thread_list ()
 {
-  struct lwp_info *lwp;
-
   /* We add/delete threads from the list as clone/exit events are
      processed, so just try deleting exited threads still in the
      thread list.  */
@@ -3725,7 +3727,7 @@ linux_nat_target::update_thread_list ()
 
   /* Update the processor core that each lwp/thread was last seen
      running on.  */
-  ALL_LWPS (lwp)
+  for (lwp_info *lwp : all_lwps ())
     {
       /* Avoid accessing /proc if the thread hasn't run since we last
 	 time we fetched the thread's core.  Accessing /proc becomes
@@ -3949,7 +3951,7 @@ linux_proc_xfer_memory_partial (gdb_byte *readbuf, const gdb_byte *writebuf,
 
   /* Iterate over LWPs of the current inferior, trying to access
      memory through one of them.  */
-  for (lwp_info *lp = lwp_list; lp != nullptr; lp = lp->next)
+  for (lwp_info *lp : all_lwps ())
     {
       if (lp->ptid.pid () != cur_pid)
 	continue;
diff --git a/gdb/linux-nat.h b/gdb/linux-nat.h
index b1b168d2bfee..74b5eddc1365 100644
--- a/gdb/linux-nat.h
+++ b/gdb/linux-nat.h
@@ -196,11 +196,9 @@ extern linux_nat_target *linux_target;
 
 struct arch_lwp_info;
 
-/* Structure describing an LWP.  This is public only for the purposes
-   of ALL_LWPS; target-specific code should generally not access it
-   directly.  */
+/* Structure describing an LWP.  */
 
-struct lwp_info
+struct lwp_info : intrusive_list_node<lwp_info>
 {
   lwp_info (ptid_t ptid)
     : ptid (ptid)
@@ -283,27 +281,26 @@ struct lwp_info
 
   /* Arch-specific additions.  */
   struct arch_lwp_info *arch_private = nullptr;
-
-  /* Previous and next pointers in doubly-linked list of known LWPs,
-     sorted by reverse creation order.  */
-  struct lwp_info *prev = nullptr;
-  struct lwp_info *next = nullptr;
 };
 
-/* The global list of LWPs, for ALL_LWPS.  Unlike the threads list,
-   there is always at least one LWP on the list while the GNU/Linux
-   native target is active.  */
-extern struct lwp_info *lwp_list;
+/* lwp_info iterator and range types.  */
+
+using lwp_info_iterator
+  = reference_to_pointer_iterator<intrusive_list<lwp_info>::iterator>;
+using lwp_info_range = iterator_range<lwp_info_iterator>;
+using lwp_info_safe_range = basic_safe_range<lwp_info_range>;
+
+/* Get an iterable range over all lwps.  */
+
+lwp_info_range all_lwps ();
+
+/* Same as the above, but safe against deletion while iterating.  */
+
+lwp_info_safe_range all_lwps_safe ();
 
 /* Does the current host support PTRACE_GETREGSET?  */
 extern enum tribool have_ptrace_getregset;
 
-/* Iterate over each active thread (light-weight process).  */
-#define ALL_LWPS(LP)							\
-  for ((LP) = lwp_list;							\
-       (LP) != NULL;							\
-       (LP) = (LP)->next)
-
 /* Called from the LWP layer to inform the thread_db layer that PARENT
    spawned CHILD.  Both LWPs are currently stopped.  This function
    does whatever is required to have the child LWP under the
diff --git a/gdb/linux-thread-db.c b/gdb/linux-thread-db.c
index eb2aa5ac409a..aff00dc8d40e 100644
--- a/gdb/linux-thread-db.c
+++ b/gdb/linux-thread-db.c
@@ -920,13 +920,12 @@ try_thread_db_load_1 (struct thread_db_info *info)
 
   if (info->td_ta_thr_iter_p == NULL)
     {
-      struct lwp_info *lp;
       int pid = inferior_ptid.pid ();
       thread_info *curr_thread = inferior_thread ();
 
       linux_stop_and_wait_all_lwps ();
 
-      ALL_LWPS (lp)
+      for (const lwp_info *lp : all_lwps ())
 	if (lp->ptid.pid () == pid)
 	  thread_from_lwp (curr_thread, lp->ptid);
 
diff --git a/gdb/mips-linux-nat.c b/gdb/mips-linux-nat.c
index b21c7cb2ea68..1088a7dc1b03 100644
--- a/gdb/mips-linux-nat.c
+++ b/gdb/mips-linux-nat.c
@@ -632,12 +632,9 @@ mips_linux_nat_target::region_ok_for_hw_watchpoint (CORE_ADDR addr, int len)
 static int
 write_watchpoint_regs (void)
 {
-  struct lwp_info *lp;
-  int tid;
-
-  ALL_LWPS (lp)
+  for (const lwp_info *lp : all_lwps ())
     {
-      tid = lp->ptid.lwp ();
+      int tid = lp->ptid.lwp ();
       if (ptrace (PTRACE_SET_WATCH_REGS, tid, &watch_mirror, NULL) == -1)
 	perror_with_name (_("Couldn't write debug register"));
     }
-- 
2.33.0