add Profile.@count_lock_conflicts

Author: IanButterworth

base/atomics.jl

@@ -80,6 +80,8 @@ end
 
 Atomic() = Atomic{Int}()
 
+LOCK_CONFLICT_COUNT = Threads.Atomic{Int}(0);
+
 """
     Threads.atomic_cas!(x::Atomic{T}, cmp::T, newval::T) where T
 

base/lock.jl

@@ -134,6 +134,9 @@ end
     return false
 end
 
+LOCK_PROFILING::Bool = false
+inc_lock_conflict_count() = Threads.atomic_add!(Threads.LOCK_CONFLICT_COUNT, 1)
+
 """
     lock(lock)
 
@@ -145,6 +148,7 @@ Each `lock` must be matched by an [`unlock`](@ref).
 """
 @inline function lock(rl::ReentrantLock)
     trylock(rl) || (@noinline function slowlock(rl::ReentrantLock)
+        LOCK_PROFILING && inc_lock_conflict_count()
         c = rl.cond_wait
         lock(c.lock)
         try

stdlib/Profile/src/Profile.jl

@@ -10,6 +10,7 @@ Profiling support.
 - `Profile.print()` to print the report.
 - `Profile.clear()` to clear the buffer.
 - Send a $(Sys.isbsd() ? "SIGINFO (ctrl-t)" : "SIGUSR1") signal to the process to automatically trigger a profile and print.
+- `@count_lock_conflicts foo()` to count how many times a task had to wait to acquire a lock.
 
 ## Memory profiling
 - `Profile.Allocs.@profile [sample_rate=0.1] foo()` to sample allocations within a specific call. A sample rate of 1.0 will record everything; 0.0 will record nothing.
@@ -44,7 +45,7 @@ const nmeta = 4 # number of metadata fields per block (threadid, taskid, cpu_cyc
 # deprecated functions: use `getdict` instead
 lookup(ip::UInt) = lookup(convert(Ptr{Cvoid}, ip))
 
-export @profile
+export @profile, @count_lock_conflicts
 
 """
     @profile
@@ -63,6 +64,26 @@ macro profile(ex)
     end
 end
 
+
+"""
+    @count_lock_conflicts
+
+`count_lock_conflicts <expression>` runs your expression while monitoring how many times a task had to wait
+to acquire a lock.
+"""
+macro count_lock_conflicts(ex)
+    return quote
+        Base.LOCK_PROFILING = true
+        Threads.LOCK_CONFLICT_COUNT[] = 0
+        try
+            $(esc(ex))
+        finally
+            Base.LOCK_PROFILING = false
+        end
+        println("$(Threads.LOCK_CONFLICT_COUNT[]) lock conflicts")
+    end
+end
+
 # An internal function called to show the report after an information request (SIGINFO or SIGUSR1).
 function _peek_report()
     iob = IOBuffer()