diff --git a/NEWS.md b/NEWS.md
index a0274f403e66c9..eb9eea9ae7eea0 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -88,6 +88,7 @@ Multi-threading changes
 * `@threads` now allows an optional schedule argument. Use `@threads :static ...` to
   ensure that the same schedule will be used as in past versions; the default schedule
   is likely to change in the future.
+* New function `Base.Threads.foreach(f, channel::Channel)` for multithreaded `Channel` consumption ([#34543]).
 
 Build system changes
 --------------------
diff --git a/base/gcutils.jl b/base/gcutils.jl
index 5d6d8fc2c5805a..72882d68b8638f 100644
--- a/base/gcutils.jl
+++ b/base/gcutils.jl
@@ -91,6 +91,16 @@ Control whether garbage collection is enabled using a boolean argument (`true` f
 """
 enable(on::Bool) = ccall(:jl_gc_enable, Int32, (Int32,), on) != 0
 
+"""
+    GC.enable_finalizers(on::Bool)
+
+Increment or decrement the counter that controls the running of finalizers on
+the current Task. Finalizers will only run when the counter is at zero. (Set
+`true` for enabling, `false` for disabling). They may still run concurrently on
+another Task or thread.
+"""
+enable_finalizers(on::Bool) = ccall(:jl_gc_enable_finalizers, Cvoid, (Ptr{Cvoid}, Int32,), C_NULL, on)
+
 """
     GC.@preserve x1 x2 ... xn expr
 
diff --git a/base/lock.jl b/base/lock.jl
index b518766fe29fef..9d0a6b053f05ed 100644
--- a/base/lock.jl
+++ b/base/lock.jl
@@ -4,9 +4,24 @@
 """
     ReentrantLock()
 
-Creates a re-entrant lock for synchronizing [`Task`](@ref)s.
-The same task can acquire the lock as many times as required.
-Each [`lock`](@ref) must be matched with an [`unlock`](@ref).
+Creates a re-entrant lock for synchronizing [`Task`](@ref)s. The same task can
+acquire the lock as many times as required. Each [`lock`](@ref) must be matched
+with an [`unlock`](@ref).
+
+Calling 'lock' will also inhibit running of finalizers on that thread until the
+corresponding 'unlock'. Use of the standard lock pattern illustrated below
+should naturally be supported, but beware of inverting the try/lock order or
+missing the try block entirely (e.g. attempting to return with the lock still
+held):
+
+```
+lock(l)
+try
+    <atomic work>
+finally
+    unlock(l)
+end
+```
 """
 mutable struct ReentrantLock <: AbstractLock
     locked_by::Union{Task, Nothing}
@@ -44,6 +59,7 @@ function trylock(rl::ReentrantLock)
     if rl.reentrancy_cnt == 0
         rl.locked_by = t
         rl.reentrancy_cnt = 1
+        GC.enable_finalizers(false)
         got = true
     elseif t === notnothing(rl.locked_by)
         rl.reentrancy_cnt += 1
@@ -71,6 +87,7 @@ function lock(rl::ReentrantLock)
         if rl.reentrancy_cnt == 0
             rl.locked_by = t
             rl.reentrancy_cnt = 1
+            GC.enable_finalizers(false)
             break
         elseif t === notnothing(rl.locked_by)
             rl.reentrancy_cnt += 1
@@ -111,6 +128,7 @@ function unlock(rl::ReentrantLock)
                 rethrow()
             end
         end
+        GC.enable_finalizers(true)
     end
     unlock(rl.cond_wait)
     return
@@ -132,6 +150,7 @@ function unlockall(rl::ReentrantLock)
             rethrow()
         end
     end
+    GC.enable_finalizers(true)
     unlock(rl.cond_wait)
     return n
 end
diff --git a/base/locks-mt.jl b/base/locks-mt.jl
index 2a492c175c6c36..c910ee6e013186 100644
--- a/base/locks-mt.jl
+++ b/base/locks-mt.jl
@@ -61,10 +61,12 @@ Base.assert_havelock(l::SpinLock) = islocked(l) ? nothing : Base.concurrency_vio
 function lock(l::SpinLock)
     while true
         if _get(l) == 0
+            GC.enable_finalizers(false)
             p = _xchg!(l, 1)
             if p == 0
                 return
             end
+            GC.enable_finalizers(true)
         end
         ccall(:jl_cpu_pause, Cvoid, ())
         # Temporary solution before we have gc transition support in codegen.
@@ -74,13 +76,20 @@ end
 
 function trylock(l::SpinLock)
     if _get(l) == 0
-        return _xchg!(l, 1) == 0
+        GC.enable_finalizers(false)
+        p = _xchg!(l, 1)
+        if p == 0
+            return true
+        end
+        GC.enable_finalizers(true)
     end
     return false
 end
 
 function unlock(l::SpinLock)
+    _get(l) == 0 && error("unlock count must match lock count")
     _set!(l, 0)
+    GC.enable_finalizers(true)
     ccall(:jl_cpu_wake, Cvoid, ())
     return
 end
diff --git a/src/gc.c b/src/gc.c
index 4c26d6e467781f..5b69a4a1025a03 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -392,12 +392,36 @@ static void run_finalizers(jl_ptls_t ptls)
     arraylist_free(&copied_list);
 }
 
+JL_DLLEXPORT int jl_gc_get_finalizers_inhibited(jl_ptls_t ptls)
+{
+    if (ptls == NULL)
+        ptls = jl_get_ptls_states();
+    return ptls->finalizers_inhibited;
+}
+
 JL_DLLEXPORT void jl_gc_enable_finalizers(jl_ptls_t ptls, int on)
 {
+    if (ptls == NULL)
+        ptls = jl_get_ptls_states();
     int old_val = ptls->finalizers_inhibited;
     int new_val = old_val + (on ? -1 : 1);
+    if (new_val < 0) {
+        JL_TRY {
+            jl_error(""); // get a backtrace
+        }
+        JL_CATCH {
+            jl_printf((JL_STREAM*)STDERR_FILENO, "WARNING: GC finalizers already enabled on this thread.\n");
+            // Only print the backtrace once, to avoid spamming the logs
+            static int backtrace_printed = 0;
+            if (backtrace_printed == 0) {
+                backtrace_printed = 1;
+                jlbacktrace(); // written to STDERR_FILENO
+            }
+        }
+        return;
+    }
     ptls->finalizers_inhibited = new_val;
-    if (!new_val && old_val && !ptls->in_finalizer) {
+    if (!new_val && old_val && !ptls->in_finalizer && ptls->current_task->locks.len == 0) {
         ptls->in_finalizer = 1;
         run_finalizers(ptls);
         ptls->in_finalizer = 0;
@@ -1580,7 +1604,7 @@ STATIC_INLINE uintptr_t gc_read_stack(void *_addr, uintptr_t offset,
 JL_NORETURN NOINLINE void gc_assert_datatype_fail(jl_ptls_t ptls, jl_datatype_t *vt,
                                                   jl_gc_mark_sp_t sp)
 {
-    jl_printf(JL_STDOUT, "GC error (probable corruption) :\n");
+    jl_safe_printf("GC error (probable corruption) :\n");
     gc_debug_print_status();
     jl_(vt);
     gc_debug_critical_error();
@@ -3121,7 +3145,7 @@ JL_DLLEXPORT void jl_gc_collect(jl_gc_collection_t collection)
     // Only disable finalizers on current thread
     // Doing this on all threads is racy (it's impossible to check
     // or wait for finalizers on other threads without dead lock).
-    if (!ptls->finalizers_inhibited) {
+    if (!ptls->finalizers_inhibited && ptls->current_task->locks.len == 0) {
         int8_t was_in_finalizer = ptls->in_finalizer;
         ptls->in_finalizer = 1;
         run_finalizers(ptls);
diff --git a/src/julia.h b/src/julia.h
index a7f3052e59fb33..64482226d1e708 100644
--- a/src/julia.h
+++ b/src/julia.h
@@ -1719,7 +1719,6 @@ typedef struct _jl_handler_t {
     int8_t gc_state;
     size_t locks_len;
     sig_atomic_t defer_signal;
-    int finalizers_inhibited;
     jl_timing_block_t *timing_stack;
     size_t world_age;
 } jl_handler_t;
@@ -1751,8 +1750,6 @@ typedef struct _jl_task_t {
     jl_gcframe_t *gcstack;
     // saved exception stack
     jl_excstack_t *excstack;
-    // current world age
-    size_t world_age;
 
     // id of owning thread
     // does not need to be defined until the task runs
diff --git a/src/locks.h b/src/locks.h
index 6365eb681ca305..a0c7e9da7831e1 100644
--- a/src/locks.h
+++ b/src/locks.h
@@ -89,11 +89,9 @@ static inline void jl_lock_frame_pop(void)
 
 static inline void jl_mutex_lock(jl_mutex_t *lock)
 {
-    jl_ptls_t ptls = jl_get_ptls_states();
     JL_SIGATOMIC_BEGIN();
     jl_mutex_wait(lock, 1);
     jl_lock_frame_push(lock);
-    jl_gc_enable_finalizers(ptls, 0);
 }
 
 static inline int jl_mutex_trylock_nogc(jl_mutex_t *lock)
@@ -116,10 +114,8 @@ static inline int jl_mutex_trylock(jl_mutex_t *lock)
 {
     int got = jl_mutex_trylock_nogc(lock);
     if (got) {
-        jl_ptls_t ptls = jl_get_ptls_states();
         JL_SIGATOMIC_BEGIN();
         jl_lock_frame_push(lock);
-        jl_gc_enable_finalizers(ptls, 0);
     }
     return got;
 }
@@ -139,9 +135,12 @@ static inline void jl_mutex_unlock(jl_mutex_t *lock)
 {
     jl_ptls_t ptls = jl_get_ptls_states();
     jl_mutex_unlock_nogc(lock);
-    jl_gc_enable_finalizers(ptls, 1);
     jl_lock_frame_pop();
     JL_SIGATOMIC_END();
+    if (ptls->current_task->locks.len == 0 && ptls->finalizers_inhibited == 0) {
+        ptls->finalizers_inhibited = 1;
+        jl_gc_enable_finalizers(ptls, 1); // call run_finalizers (may GC)
+    }
 }
 
 static inline void jl_mutex_init(jl_mutex_t *lock) JL_NOTSAFEPOINT
diff --git a/src/rtutils.c b/src/rtutils.c
index f9a8eb59a564ef..17cadf46574e92 100644
--- a/src/rtutils.c
+++ b/src/rtutils.c
@@ -215,7 +215,6 @@ JL_DLLEXPORT void jl_enter_handler(jl_handler_t *eh)
     eh->gc_state = ptls->gc_state;
     eh->locks_len = current_task->locks.len;
     eh->defer_signal = ptls->defer_signal;
-    eh->finalizers_inhibited = ptls->finalizers_inhibited;
     eh->world_age = ptls->world_age;
     current_task->eh = eh;
 #ifdef ENABLE_TIMINGS
@@ -246,21 +245,26 @@ JL_DLLEXPORT void jl_eh_restore_state(jl_handler_t *eh)
     current_task->eh = eh->prev;
     ptls->pgcstack = eh->gcstack;
     arraylist_t *locks = &current_task->locks;
-    if (locks->len > eh->locks_len) {
-        for (size_t i = locks->len;i > eh->locks_len;i--)
+    int unlocks = locks->len > eh->locks_len;
+    if (unlocks) {
+        for (size_t i = locks->len; i > eh->locks_len; i--)
             jl_mutex_unlock_nogc((jl_mutex_t*)locks->items[i - 1]);
         locks->len = eh->locks_len;
     }
     ptls->world_age = eh->world_age;
     ptls->defer_signal = eh->defer_signal;
     ptls->gc_state = eh->gc_state;
-    ptls->finalizers_inhibited = eh->finalizers_inhibited;
     if (old_gc_state && !eh->gc_state) {
         jl_gc_safepoint_(ptls);
     }
     if (old_defer_signal && !eh->defer_signal) {
         jl_sigint_safepoint(ptls);
     }
+    if (unlocks && eh->locks_len == 0 && ptls->finalizers_inhibited == 0) {
+        // call run_finalizers
+        ptls->finalizers_inhibited = 1;
+        jl_gc_enable_finalizers(ptls, 1);
+    }
 }
 
 JL_DLLEXPORT void jl_pop_handler(int n)
diff --git a/src/task.c b/src/task.c
index 06e6d4895e7d76..5891b877b4b459 100644
--- a/src/task.c
+++ b/src/task.c
@@ -319,9 +319,8 @@ static void ctx_switch(jl_ptls_t ptls)
     }
 
     // set up global state for new task
-    lastt->world_age = ptls->world_age;
     ptls->pgcstack = t->gcstack;
-    ptls->world_age = t->world_age;
+    ptls->world_age = 0;
     t->gcstack = NULL;
 #ifdef MIGRATE_TASKS
     ptls->previous_task = lastt;
@@ -404,8 +403,14 @@ JL_DLLEXPORT void jl_switch(void)
     else if (t->tid != ptls->tid) {
         jl_error("cannot switch to task running on another thread");
     }
+
+    // Store old values on the stack and reset
     sig_atomic_t defer_signal = ptls->defer_signal;
     int8_t gc_state = jl_gc_unsafe_enter(ptls);
+    size_t world_age = ptls->world_age;
+    int finalizers_inhibited = ptls->finalizers_inhibited;
+    ptls->world_age = 0;
+    ptls->finalizers_inhibited = 0;
 
 #ifdef ENABLE_TIMINGS
     jl_timing_block_t *blk = ct->timing_stack;
@@ -427,7 +432,12 @@ JL_DLLEXPORT void jl_switch(void)
     assert(ptls == refetch_ptls());
 #endif
 
-    ct = ptls->current_task;
+    // Pop old values back off the stack
+    assert(ct == ptls->current_task &&
+           0 == ptls->world_age &&
+           0 == ptls->finalizers_inhibited);
+    ptls->world_age = world_age;
+    ptls->finalizers_inhibited = finalizers_inhibited;
 
 #ifdef ENABLE_TIMINGS
     assert(blk == ct->timing_stack);
@@ -680,6 +690,7 @@ STATIC_OR_JS void NOINLINE JL_NORETURN start_task(void)
     jl_ptls_t ptls = jl_get_ptls_states();
     jl_task_t *t = ptls->current_task;
     jl_value_t *res;
+    assert(ptls->finalizers_inhibited == 0);
 
 #ifdef MIGRATE_TASKS
     jl_task_t *pt = ptls->previous_task;
diff --git a/stdlib/Distributed/src/messages.jl b/stdlib/Distributed/src/messages.jl
index bbfb13f276fa53..f8e1da156babcb 100644
--- a/stdlib/Distributed/src/messages.jl
+++ b/stdlib/Distributed/src/messages.jl
@@ -147,6 +147,7 @@ function flush_gc_msgs(w::Worker)
     end
 
     # del_msgs gets populated by finalizers, so be very careful here about ordering of allocations
+    # XXX: threading requires this to be atomic
     new_array = Any[]
     msgs = w.del_msgs
     w.del_msgs = new_array
@@ -178,7 +179,7 @@ function send_msg_(w::Worker, header, msg, now::Bool)
         wait(w.initialized)
     end
     io = w.w_stream
-    lock(io.lock)
+    lock(io)
     try
         reset_state(w.w_serializer)
         serialize_hdr_raw(io, header)
@@ -191,7 +192,7 @@ function send_msg_(w::Worker, header, msg, now::Bool)
             flush(io)
         end
     finally
-        unlock(io.lock)
+        unlock(io)
     end
 end
 
diff --git a/test/core.jl b/test/core.jl
index baf256a6eaf94b..8e12e4bc5bc979 100644
--- a/test/core.jl
+++ b/test/core.jl
@@ -6,7 +6,6 @@ using Random, SparseArrays, InteractiveUtils
 
 const Bottom = Union{}
 
-
 # For curmod_*
 include("testenv.jl")
 
@@ -2071,7 +2070,7 @@ mutable struct A6142 <: AbstractMatrix{Float64}; end
 +(x::A6142, y::AbstractRange) = "AbstractRange method called" #16324 ambiguity
 
 # issue #6175
-function g6175(); print(""); (); end
+function g6175(); GC.safepoint(); (); end
 g6175(i::Real, I...) = g6175(I...)
 g6175(i, I...) = tuple(length(i), g6175(I...)...)
 @test g6175(1:5) === (5,)
@@ -2211,7 +2210,7 @@ day_in(obj6387)
 function segfault6793(;gamma=1)
     A = 1
     B = 1
-    print()
+    GC.safepoint()
     return
     -gamma
     nothing
@@ -3317,7 +3316,7 @@ function f11065()
         if i == 1
             z = "z is defined"
         elseif i == 2
-            print(z)
+            print(z) # z is undefined
         end
     end
 end
@@ -4234,7 +4233,10 @@ end
 end
 # disable GC to make sure no collection/promotion happens
 # when we are constructing the objects
+get_finalizers_inhibited() = ccall(:jl_gc_get_finalizers_inhibited, Int32, (Ptr{Cvoid},), C_NULL)
 let gc_enabled13995 = GC.enable(false)
+    @assert gc_enabled13995
+    @assert get_finalizers_inhibited() == 0
     finalized13995 = [false, false, false, false]
     create_dead_object13995(finalized13995)
     GC.enable(true)
diff --git a/test/misc.jl b/test/misc.jl
index d8593c8351d3b6..c4d26e3b223b95 100644
--- a/test/misc.jl
+++ b/test/misc.jl
@@ -87,9 +87,12 @@ let
     @test occursin("f()", warning_str)
 end
 
+# Debugging tool: return the current state of the enable_finalizers counter.
+get_finalizers_inhibited() = ccall(:jl_gc_get_finalizers_inhibited, Int32, (Ptr{Cvoid},), C_NULL)
+
 # lock / unlock
 let l = ReentrantLock()
-    lock(l)
+    @test lock(l) === nothing
     @test islocked(l)
     success = Ref(false)
     @test trylock(l) do
@@ -102,14 +105,43 @@ let l = ReentrantLock()
     @test success[]
     t = @async begin
         @test trylock(l) do
-            @test false
+            error("unreachable")
         end === false
     end
+    @test get_finalizers_inhibited() == 1
     Base.wait(t)
-    unlock(l)
+    @test get_finalizers_inhibited() == 1
+    @test unlock(l) === nothing
+    @test get_finalizers_inhibited() == 0
     @test_throws ErrorException unlock(l)
 end
 
+for l in (Threads.SpinLock(), ReentrantLock())
+    @test get_finalizers_inhibited() == 0
+    @test lock(get_finalizers_inhibited, l) == 1
+    @test get_finalizers_inhibited() == 0
+    try
+        GC.enable_finalizers(false)
+        GC.enable_finalizers(false)
+        @test get_finalizers_inhibited() == 2
+        GC.enable_finalizers(true)
+        @test get_finalizers_inhibited() == 1
+    finally
+        @test get_finalizers_inhibited() == 1
+        GC.enable_finalizers(false)
+        @test get_finalizers_inhibited() == 2
+    end
+    @test get_finalizers_inhibited() == 2
+    GC.enable_finalizers(true)
+    @test get_finalizers_inhibited() == 1
+    GC.enable_finalizers(true)
+    @test get_finalizers_inhibited() == 0
+    @test_warn "WARNING: GC finalizers already enabled on this thread." GC.enable_finalizers(true)
+
+    @test lock(l) === nothing
+    @test try unlock(l) finally end === nothing
+end
+
 # task switching
 
 @noinline function f6597(c)